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BRISBANE VOLUME 36 10 AUGUST, 1994 PART 2

SCALLOP FISHERIES IN SOUTHERN AUSTRALIA: MANAGING FOR STOCK RECOVERY

WILL ZACHARIN

Zachann, W. 1994 08 10: Scallop fisheries in southern Australia: managing for stock recovery, Memoirs of the Queensland Museum 36(2). 241-246. Brisbane. ISSN 0079-

8835,

Scallop fisheries in southern Australia are showing signs of stock recovery after a

period of

low abundance. The recovery has been sporadic and slow although large areas of the fishing grounds have been subject to little or no fishing for upto 5 years. New management strategies designed to encourage stock recovery and promote sustainable harvests in the future are in place. Management strategies and fishery monitoring programs are presented.

Will Zacharin, Sea Fisheries Division, Department of Primary Industry and Fisheries, GPO Box 619F. Hobart, Tasmania 7001, Australian, 15 April, 1994

There are 5 distinct commercial scallop fishing zones m southern Australia : Port Phillip Bay and Lakes Entrance in Victoria; the greater area of Bass Strait (known as the Central Zone), the 20 nautical mile zone around the north coast of Tas- mania called the Tasmanian Zone, and the east coast of Tasmania (Fig.1). They are geographi- cally distinct in terms of their historical catch and fleet dynamics. Management is under the control of 3 separate authorities; the Victorian and Tas- manian State Governments and the Common- wealth Government (Australian Fish Man- agement Authority). Three different management strategies are operating.

The Bass Strait Scallop Consultative Commit- tee (BSSCC) formed in 1991 to develop a rational management plan for scallop fisheries across Bass Strait, This was the second time in the fisheries’ history that such a process had been attempted (Zacharin, 1990, 1991), An earlier plan developed by the Bass Strait Task Force which recommended that the fisheries" jurisdiction be split between Victoria and Tasmania was not effectively implemented (Zacharin, 1990). Fishermen and managers recognised that future harvesting strategies needed to be based on cur- reni biological knowledge of the species (in regard to reproductive maturity and growth rates), fleet dynamics and the need for economic efficiency. The committee drafted a management plan with 5 main objectives: I, to control fishing effort to a level which is consistent with the current state of knowledge of scallop stocks; 2, to encourage investigation and modification of the most appropriate fishing equipment and fishing practices to improve catch efficiency and to min- imise damage to the scallop beds; 3, to allow further scientific and other data to be collected so

that management decisions can be based on a sound understanding of biological and operation- al characteristics of the fishery; 4, to allow an effective level of recruitment to the fishery by prohibiting the taking of scallops of «80mm with a view to allowing adult stocks to complete at least two major spawnings before harvest; and 5, to allow participants to maximise their return from harvesting the scallop resource. (Bass Strait Scallop Management Plan 1952, Commonwealth Fisheries Act 1991).

The resultant management strategy combines input and output controls to restrict the number of fishers; to prohibit the taking of small scallops; to contro] scallop landings and to provide a level of profitability to the fleet.

CONTROLS ON FISHING

In the past, both the States and the Common- wealth restricted fishing activitics by imposing input controls, such as closed seasons, size limits and dredge restrictions. Over the past 4 years there has been a shift towards output controls as they are perceived to be more effective in manag- ing catch and controlling quality, provided that the necessary level of monitonng and enforce- ment is present. A size limit of 80mm at widest diameter, however, still exists. The two main strategies of the new management plan for the Central Zone of Bass Strait are the * 20% trashing rate’ requirement and the 'two-spawnings' criterion. The 20 % trashing rate was designed as a yield optimisation strategy, through limiting the capture of, and minimising incidental mortality to small (<80mm at widest diameter) scallops. The ‘two spawning’ criterion is a parallel manage- ment requirement designed to allow scallops two

242

MEMOIRS OF THE QUEENSLAND MUSEUM

FIG.1. Southern Australian scallop fishery divided into 5 distinct zones. Port Phillip Bay (1), Lakes Entrance (2), Bass Strait (3), northern Tasmania (4), and eastern Tasmania (5).

major spawnings prior to their being fished, without regard to size. Thus scallops need both to have spawned twice and have less than 20% of the catch smaller than 80mm at widest diameter prior to their being fished.

The trashing rate is the proportion of small scallops discarded over a fishing ground during

commercial operations. If more than 20% of the catch landed on the sorting tray is being retumed to the water, fishermen are required to cease fishing in the area until scallop size increases. This is not difficult for the majority of Bass Strait scallop beds as they are usually of the one size or age class. However, in the event of two age

SCALLOP STOCK RECOVERY, SOUTHERN AUSTRALIA

classes being mixed in the one area, a 20% trash- ing rate is considered acceptable, having regard for increasing mortality in the older age class, and the potential of predators to significantly reduce the remaining scallops on a fished bed,

Failure of fishermen to leave the area can result in a 3 month closure to the whole fishery, This closure can be implemented by the management committee under a specific provision in the Bass Strait scallop management plan.

Application of trashing rates are not new in shellfish management. A trashing rate of not more than 30% of landed catch was introduced into the eastem U.S offshore clam fishery in 1983. The reason was lo prevent wastage due 10 excessive discarding and to mect minimum size requirements (Murawski & Serchuk, 1989).

Two major spawnings from adults, prior to their being fished, are considered essential if sufficient reproductive output from the fishery 1s to occur. Commercial scallops in Bass Strait have their first major spawning in their second year {1+ age class). However, fecundity is relatively low at this age(R. McLouglin pers. comm.) and therefore delaying the fishing until the scallops’ second major spawning is desirable to increase the prob- ability of some recruitment from that particular age class of adult spawners. Restricting fishing operations even further until a third major spawn- ing has occurred cannot be defended, as natural mortality is thought to be high in Bass Strait populations after scallops reach an age of four years, High levels of predation by starfish on commercial scallop beds have been observed on a number of occasions,

Delaying the time of first capture till after the second spawning has a number of other benefits, Scallops have another year's growth, which results in the majority of the population reaching a shell height 70mm (shell width 80mm), In- dividual yields increase c.30%, and the landed value of the fishery should nse, There is ап as- sumption that there is no rapid increase in natural mortality. A yield optimisation mode! needs to be completed to support this assumption.

The crux of the management plan ts, if the trashing rale is below 20%, then it can be assumed that the bed should be fished until it is no longer economically viable to continue. After fishing scallops will stil] remain in the area but at a low density.

CATCH RESTRICTIONS The Buss Strait fishery opens on 1 April of each

243

year and closes in late December. This summer closure protects juveniles from dredge damage and stops scallops with poor meat condition being landed, In most years, post spawning meat and gonad condition does not improve unti] March, Scallop landings are subject to ‘quota’, set per trip or forinightly. At present the quota is 150 units per fortnight; a unit being a black polypropylene onion bag measuring 900mm x 580mm and having a volume of 0.08 m?. This measure owes its derivation to the past availability and suit- ability of onion bags for landing scallops.

While the fortnightly quota does reduce fishing effort to some extent, this is not its primary pur- pose, It is à marketing too] which provides for the landing of quality scallops and prevents wastage due to time delays in Janding and processing larger volumes. It prevents a ‘gold rush’ event, as occurs when there isa competitive total allowable catch, The catch quota was agreed through negotiation between Government, fishermen and the processing sector, If costs of fishing rise and landed price falls or even remains steady, it 3s possible for the industry to re-negotiate the catch quota at any time. Profitability of the fleet is a main objective of the management plan.

Catch is also controlled in the Victorian and Tasmanian Zones. In Victoria a weekly catch limit is currently operating, while in Tasmania, a ‘per tip’ limit will continue to operate when fishing recornmences in the future.

QUOTA MONITORING AND CATCH DATA

Each unit or bag landed must have a plastic colour-coded tag attached. Tags are issued each month in advance by the Australian Fish Manage- menl Authority, Unused tags are retumed as а cost saving measure and are re-issued the follow- ing year but in a different month. Numerical coding also changes each month and year to ensure unused tags will not be held over from year 10 year, The tag system allows efficient monitor- ing and enforcement óf the quota, and in provid- ing a validation system for scallop landings through the processing sector.

А new logbook introduced in 1992 15 based on a 7 x 7 nautical mile grid. Retums are filled out for each trip and data entered on a central com- puter database in Hobart. The system will give à better assessment of fleet dynamics, exploitation rates and total landed catch from the Central Zone. 1n the past the fleet has provided catch returns without meaningful spatial data to the State authority in which the vessel was based,

244

Consequently, no comprehensive analysis of the fishery has been possible. Victorian and Tas- manian fishery managers continue to collate their own catch returns from the inshore 20 nautical mile zones.

LICENSING

All 3 jurisdictional zones are теў entry fisheries and no new licences will be issued. There are 165 vessels licensed to fish in the Central Zone. Of these 73 are based in Tasmania and 92 in Victoria. Licences in Victoria are trans- ferable and have been for the better part of the 30-year history of the fishery. In Tasmania, limited entry was not introduced until 1986 with transferability following in 1992 (Zacharin, 1990), Central Zone licences are stil] non-trans- ferable pending the development of options for reducing the number of participants in the fishery. Tt is desirable that the issue of transferability be resolyed, as Central Zone licences cannot be split from State scallop licences, which are trans- ferable. It would be highly undesirable to create a ‘third’ scallop fleet in the Central Zone of Bass Strait. An important objective of the licensing policy is to have all the Central Zone licences held by the State scallop fleets, as the inshore scallop fishing grounds have historically provided the bulk of the scallop catch, with the Central Zone providing good catches intermittently.

FISHING GEAR

The southern scallop fishery uses tooth-bar steel box dredges 2-4.5m wide. Protruding teeth on the bars range from 2.5-15cm, depending on the type of bottom sediment and the individual operator. These dredges can cause high levels of incidental damage and alternative designs are still being investigated. Evidence from dredge trials shows that up to 50% of scallops in the dredge's path may be damaged, depending on the type of bottom, length of toothbar, density of scallops and fishing practices, Dredge efficiency can be low, having been experimentally measured at 10 % (McLouglin er af,, 1991), Gear technology im- provements are important to this fishery as any reduction in incidental mortality and increases in efficiency will reduce costs and increase yields.

EFFECTIVENESS OF MANAGEMENT STRATEGIES

The new plan for the Central Zone has yel lo be

MEMOIRS OF THE QUEENSLAND MUSEUM

tested under rigorous fishing operations duc to the low level of commercial fishing operations. Mechanisms such as at-sea monitoring and shore based market measurers will provide for a quick response to any problems that anse with regard to scallop size. The Victorian fishery has been operating under à tag system for two ycars and the scallop industry seems pleased with the progress of this system.

Any management plan for the southern scallop fishery should be complementary between Vic- torian and Tasmanian authorities. The new plan for the Central Zone goes a long way towards achieving this; however, further gains may be difficult because of the differences in fleet dynamics between the two States,

The Victorian scallop fishery has a single licensed fleet that is heavily depreciated and lar- gely reliant on annual scallop fishing seasons, In Tasmania the multi-purpose fishing fleet has evolved with the majority of scallop licences being on vessels with rock lobster entitlements, Other Tasmanian scallop vessels are licensed to drop-line, trawl or take shark during a closed scallop season. These differences in dynamics between the Victorian and Tasmanian fleets have resulted in each having different economic con- straints. The zoning of the Bass Strait scallop fishery needs to be retained to enable the subtle differences in management priorities to operate, as appropriate for each State's fishing industry.

RESEARCH AND DEVELOPMENT REQUIREMENTS

Six future research needs, identified for the southern scallop fishery by Ihe Bass Strait Management Committee, are listed in order of prioritv: 1, confirmation that Bass Strait scallops consist of a single stock; 2, development of an efficient and reliable recruitment monitoring technique to provide an index of annual spatfall; 3, development of statistically reliable survey techniques for assessing biomass on individual beds; 4, assessment of the overall impact of predation by starfish (Coscinasterias sp.) on scal- lop populations; 5, investigation of recruitment enhancemenvsea ranching of scallops as per the New Zealand model; and 6, investigation of dif- ferences in growth rates and fecundity schedules for scallops in different regions of Bass Strait (Bass Strait Scallop Management Committee 1992, mimeo),

The second priority is important in providing a measure of success of the management plan,

SCALLOP STOCK RECOVERY, SOUTHERN AUSTRALIA

specifically the iwo-spawning criterion. A recruitment index also provides early warning of recruitment failure or 'above-average' recruil- ment success.

The impact of predatory starfish was demonstrated to be of considerable importance in 1992. An identified scallop bed east of Deal Is- land in Bass Strait was decimated by starfish during a delay to fishing, in an attempt to conform to the two-spawning criterion and improve scal- lop yields. Further investigation of these predators is necessary to prevent such an occur- rence happening again.

PROGNOSIS FOR 1993 AND BEYOND

There has been a significant recovery of scallop stock(s) in both Port Phillip Bay and off Lakes Entrance in Victoria. A large settlement occurred inthe spring of 1990 with subsequent recruitment to the fisheries in 1992. Further settlement has been observed in cach of the following years and the fisheries are showing good prospects for the next one to two years (Zacharin - pers. obs.), It is ironic that the beds off Lakes Entrance (which have been sporadically fished) have recovered before the scallop grounds in Tasmania (where the fishery has been closed for five years), In this instance, total closure of the frshery has not lead to any earlier stock recovery than has been ob- served in Victorian waters, where fishing con- tinued. However, there is no certainty that the factors affecting recruitment off Lakes Entrance apply over a much wider area, and no conclusions can be made in terms of management for stock recovery.

Recent exploratery excursions into the Central Zone and the northern Tasmanian Zone have shown that juvenile scallops are present over a wide area. If these juveniles successfully recruit into the fishery in 1993 and 1994, an economical- ly viable fishery will again operate in the Tas- maman and Central Zones,

LESSONS TO BE LEARNT

The recovery of the Victorian scallop grounds, through what appears in Port Phillip Bay to be due to an enormous settlement event in 1991, is dif- ficult to explain. The residual stock in the hay was apparently at an all time low at 19 million, but one of the largest recorded settlements has occurred. The estimated abundance is in excess of 800 million scallops (D. Molloy, pers. comm.). This is another example of the critical influence of

245

environmental variables on successful spawning events, settlement and subsequent recruitment. Stock/recruit relationships of P. fumatus in southern Australia appear to be extremely noisy if they exist at all. These observations support the new strategy of allowing two major spawnings before harvesting. particularly in the offshore fisheries where retention of spat over scallop grounds will be more variable than in the enclosed environs of Port Phillip Bay.

It is important to remember that the scallop fleets of Victoria and Tasmania are different in terms of their level of capital investment, vessel specifications, fishing patterns and reliance on the scallop resource for income. No hard and fast management plan across the three existing zones will be successful in meeting both States’ ad- ministrative and economic requirements. Com- plementary management plans that take account of these differences are preferable to continued friction between the two State based fleets. One needs to be aware that the majority of the histori- cal catch has come from the state 20 nautical mile zones, the Central Zone resource being one of sporadic opportunity.

Change for its own sake can be a destructive policy. The success or otherwise of the current management plan operating in the southem scal- lop fishery should be assessed before major chan- ges are contemplated. Feedback on the effects of the trashing rate and two spawning strategy will not be evident for two to three years, With the new logbook providing better spatial information on catch, an integrated catch datahase system and progression towards developing a recruitment index or forecasting system, management of the scallop resources in southern Australia can only improve,

The Australian Fish Management Authority will probably relinquish responsibility for the Bass Strait scallop fishery 1n 1994 and leave joint management to the Victorian and Tasmanian agencies, A jurisdictional line would be drawn for the purpose of monitoring and enforcement responsibilities. The existence of remaining Bass Strait permits for the Central Zone which are not attached to state scallop licences may impede this process,

ACKNOWLEDGEMENTS

Thanks are due to the many members of the Bass Strait Scallop Consultative Committee for plugging away at а new management plan after ten years of mectings at all manner of manage-

246

ment committees and venues. I would also thank two anonymous referees for suggesting improve- ments to this manuscript.

LITERATURE CITED

COMMONWEALTH FISHERIES ACT 1991: BASS STRAIT SCALLOP MANAGEMENT PLAN 1992.

MCLOUGLIN, R.J, YOUNG, P.C., MARTIN, R.B. & PARSLOW, J. 1991. The Australian scallop dredge: estimates of catching efficiency and as- sociated indirect fishing mortality. Fishery Re- search 11: 1-24,

MEMOIRS OF THE QUEENSLAND MUSEUM

MURAWSKI, S.A. & SERCHUK, F.M. 1989. Mechanized shellfish harvesting and its manage- ment: the offshore clam fishery of the eastern United States. Pp. 479-506. In Caddy, J.F., (ed.), ‘Marine invertebrate fisheries’.

ZACHARIN, W.F 1990. Scallop fisheries manage- ment: the Tasmanian experience. Pp. 1-11. In Dredge, M.L.C., Zacharin, W.F. & Joll, L.M., (eds), ‘Proceedings of the Australasian Scallop Workshop Hobart 1988'. (Tasmanian Govern- ment Printer: Hobart).

ZACHARIN, W.F. 1991. Slow recovery for Bass Strait scallops. Australian Fisheries 50(1): 28—30.

POPULATION AND BIOLOGY OF THE COMMERCIAL SCALLOP (PECTEN FUMATUS) IN JERVIS BAY, NSW

HECTOR R. FUENTES

Fuentes, H.R, 1994 08 10; Population and biology of the commercial scallop (Pecten Jumatus) in Jervis Bay, NSW. Memoirs of the Queensland Museum 362): 247-259. Brisbane, ISSN 0079-8835,

Following a peak jn 1981/82, the commercial scallop fishery in Jervis Bay declined to the point where the dredge fishery finished in 1984 and the dive fishery in 1989-90. Despite past economic importance, little information was available on the biology of Pecten fumatus in Jervis Bay, Two small, low density, scallop beds in the south and north of the bay had different densities. Most scallops were found at depths of 15-20m. Density increased from 1990 to 1992. Recruitment events occurred in November 1989, November 1990 and in March 1991, Three groups that may be age classes 0+, 1+ and 2+ years were identified in each year. Lower reproductive activity occurred from December to March and 3 or 4 periods of higher activity occurred between April and December, suggesting multiple spawning behaviour. There was poor correlation between water temperature and gonad index, but significant correlation was found between increasing numbers of parasitised scallops and period of increasing water temperature. Main settlement occurred from November to January. It appears that there are factors which prevent successful settlement in locations other than the two main beds. There was a greater settlement at depths of 8-14m.

Hector R. Fuentes, NSW Fisheries, Fisheries Research Instilute, Р.О. Box 21, Cronulla, New South Wales 2230, Australia; Present address; Queensland Deparment of Primary In- dustries, Northern Fisheries Centre, P.O. Box 5396, Cairns, Queensland 4870; 23 May, 1994.

In 1988 à study was initiated in Jervis Bay to provide baseline information on commercial molluscs for a management plan. Four species are of economic interest but this study deals only with the commercial scallop (Pecten fumatus), which has been the basis of an intermittent fishery since 1970,

Historical information (Hamer & Jacobs, 1987; Young & Martin,1989) suggests that commercial scallop harvests in NSW were high in the early 1970's, but there is no indication of the total production in Jervis Bay. However, during the fiscal year 1981—1982 the fishery reported 2,822 tonnes (Stewart et al.,1991) for NSW with 1,329 tonnes comming from Jervis Bay. Anecdotal in- formation suggests that up to 35 dredge boats and an unknown number of commercial scallop divers were operating in the bay during the 1981— 1982 peak in the fishery. The dredge boats stopped operating in 1983-84 when the scallop fishery became uneconomic. The divers persisted until the end of 1990, although they have har- vested <10 tonnes per annum in recent years. Recreational divers harvest scallops in Jervis Bay, hit there are no catch estimates. Due to the low density of scallops, the NSW Department of Fisheries recommended a total closure of the

fishery from November, 1991 to June, 1994. to allow stock recovery.

The aims of population level work were to provide information on distribution, abundance, size composition and settlement. The aim of work at the individual level was to increase the knowledge of the reproductive cycle.

MATERIALS AND METHODS

POPULATION SURVEYS

The distribution and abundance of scallops (Fig.1) were estimated during grid and transect dive surveys during 1989-1991 (Fuentes et al., 1992). Random transect surveys in February 1990 and 1991 (Fuentes et al.,1992) examined populations in areas identified during grid sur- yeys as having high concentrations of scallops. In April 1992, 35 transects were allocated to each area. In the transect surveys, scallops were clas- sified according to size: small (flat shell «30mm), medium (30-60mm) and large (760mm). The length categories were chosen on basis of the length-age relationships (Hamer, 1987). Transects containing scallops were grouped into: high density transects (70.1 seal Im?) and low density transects («0.1 scal/m?),

Population size structure was based on length-

248

Jervis Bay

Honeymoon Вау r^

x E 2 F z

FIG.1. Location of Jervis Bay.

frequency surveys in the Murrays Beach bed (Fuentes et al.,1992). Only data from surveys between September, 1989 and August, 1991 are included herein. All samples were taken from the Murrays Beach bed by 2-3 divers who collected all scallops that they saw during 40—50min dives in 17-20m. The collections were assumed to es- timate the actual length- frequency distribution of scallops in the bed.

REPRODUCTIVE BIOLOGY

Regular collections of 50 scallops of commer- cial size (>65mm) were taken by SCUBA divers from the Murrays Beach bed. Monthly or fortnightly samples were taken according to the state of the gonads. Based on the assumption that the gonad weight of mature individuals changes in relation to total body weight during the breed- ing season, a gonosomatic index (GSI) was used as indicator of reproductive condition (Grant & Tyler,1983; Barber & Blake,1991). A GST was calculated for each nonparasitised scallop: GSI = (GW/BW — GW) * 100, where GW is the gonad weight and BW is the body weight in grams. Mean GSI values and frequencies of parasitised scallops were correlated to weekly bottom temperatures from near the collecting site.

MEMOIRS OF THE QUEENSLAND MUSEUM

Macroscopic and microscopic examinations of gonads were conducted to investigate scallop reproductive behaviour and to implement an easy and rapid technique to assess the reproductive condition of scallops. In the macroscopic study, dissected gonads were classified into 7 stages: Immature, Developing 1, Developing 2, Ripe, Spawning 1, Spawning 2 and Parasitised. In the microscopic study, the female sections of the gonads were classified into 9 stages: Immature, Early development, Ripe, Partial spawning, Ex- tensive spawning, Resorption, Resting and Parasitised,

SETTLEMENT

A longline system with collector bags acting as artificial substrata was used to study the spatial and temporal characteristics of scallop settle- ment. From August 1989 to February 1990 settle- ment was studied near the Murrays Beach and Honeymoon Bay scallop beds. From August 1990 to February 1991, Plantation Point, Huskis- son and Green Point were added for settlement studies. For detailed descriptions of the sampling design and location of collectors see Fuentes et al. (1992),

“wo ON P И ѓ | i / M d r | »/ H ) (il i { |^ | J ү Н Y 4] | MES 7 | 4 I H | 1 [| Ае E ERN T, / į ~ ] f y Н j t / MNA „ \ 4 Ty \ É Lu N [| j MEA ; \ =wGorman and ]оһп=шт 1972 N ~ Dames and Moore 1985. 0 5 © fuentes et al 1997 ы = d

FIG.2. Distribution changes of the commercial scal- lop, P. fumatus, inJervis Bay. The straight line is the boundary between State and Commonwealth waters.

POPULATION BIOLOGY, Р. FUMATUS, JERVIS BAY

249

(Butcher et al.,1981) and a

E ELM number of other studies "A (Jacobs,1983; Hamer,1987; O^ sos Hamer & Jacobs,1987; Wil-

| | Bowen llam /

и liams & Diver,1988; Fuentes et al.,1992) indicated that P. fumatus occurred throughout the bay (Fuentes et al.,1990). Commercial scallops were primarily confined to Murrays Beach and Honeymoon Bay (Fig.2), with only few in- dividuals observed elsewhere. More scallops were found be- tween 15-20m than between 5-15m. What constrained the commercial scallop to this dis- tribution is unknown, but natural environmental chan-

FIG.3. Location of transects at Murrays Beach Bed in April 1992. Figures ges, fishing methods, over-

on the circles are transect numbers.

RESULTS AND DISCUSSION

POPULATION SURVEYS

DISTRIBUTION: The first assessments of commer- cial scallop distribution including abundance were obtained from the dredge surveys conducted by FRV Kapala during the 1970 and 1971 peak in the scallop fishery (Gorman & Johnson, 1972). No further scallop investigations were conducted in Jervis Bay until the fishery boomed again in the early 1980's. At this time a dive survey

fishing or a combination of fac- tors should be examined.

Dredging was the most common method of harvesting scallops in Jervis Bay during the years of intensive fishing. Although some studies have alleged that dredging has no adverse effect on scallops (Butcher et al.,1981), other authors have suggested that dredges both cause considerable damage to scallops that are left in the dredge track (Caddy,1973, McLoughlin et al.,1991) or cause detrimental changes to the bottom (McLoughlin et al.,199], Riemann and Hoffmann, 1991) which prevent or inhibit scallop settlement. However, it

TABLE 1. Sampling effort and abundance of scallops in the two main scallop beds in Jervis Bay during transect

dives in February 1990, February 1991 and April 1992,

|. MumaysBeach _ | — HoneymoonBay — | TOTAL —— |

| 1992 | 1990 | 1991 | 1992 | 1990 | 1991 | 1992 | [memes | s | s [s px pss emm] Ы мастава шэ | 20 | zwo | 2100 | zoso f 2,00 2.0 | амо | аю | s200 | 95 | 103 | 101 | ==

| m | m | m | m | | 16 | as | m | 20 | з | 15 | 36 | 38 | егш Poe. e a | же ш

pom T [юу | | Transects with scallops | 19 | | Total scallops

| Small scallops(<30mm) | 21 | 76 | 9 | [Medium (31-6omm) | | Large scallops (>60mm) |

Densi per m "

mm аз mu sm M M Wm NE E. E | s | a |29 | æ | m | в | no | 5 | Мезон | та ] 75 | зз] эз | 27 [Mean scallops/allwansects| 43 | 43 | 390 | 12 | o9 | as | 24 | 26 | ол» | 0.125 | oso | | тош density (perm?) | 0071 | 0071 | osso | oom | oos | оовт | оо | ооз | Q075 |

2.6 21.7 | ооз! | бов | 0.124 | 0.096 | 0095 | 0577 |

include only transects with scallops.

183

[30 | | 742 | 58 | s7 | 3466 |

250

FIG.4, Survey areas showing the differential abundance of commercial scallops in the Murrays Beach Bed during the transect survey in April 1992.

is still not known if fishing technique was the only factor responsible for a decrease in these fisheries.

ABUNDANCE: Dredge surveys and dive surveys provide similar estimates of scallop distributions (McShane,1982; McShane & O'Connor,1982); however, dive surveys yield more precise es- timates of abundance although the estimates typi- cally are lower, There were no dredge vessels operating in Jervis Bay during the time of this study, therefore, only estimates from dive sur- veys were available.

The Murrays Beach bed typically contained a relatively low density of scallops, and the Honeymoon Bay bed was even more sparcely populated. However, a comparison of tran- sect surveys in 1992 with pre- vious surveys in 1990 and 1991 (Table 1) indicated differences in the abundance of the three size classes and an increase in the | total number of scallops. At both locations, the number of medium size scallops were more abundant in 1992 than in previous years. which suggest improved recruit- ment to the fishery,

In the 1992 transect survey at the Murrays Beach bed, scallops were found in only 23 transects.

| Итен Inland

[Densityitranseet| 0.130 | 0.223 | 0.037 | 0.039 | 20 | &o | 78 | | high density |

Лом density | 0.035 | 0047 | 0.022 | 0006 | i2 | 60 |

MEMOIRS OF THE QUEENSLAND MUSEUM

The average number of scallops in all transects was 0.99] scal/m? (SE = +0.264). The location and scallop density for each transect (Fig. 3) identified the E-W boundaries of the bed, but it did not identify the northern limit of the bed which extends towards the middle of the bay. Within the bed, areas of high (>0.1scal/ m?) and low («0.1scal/m?) density were identified (Fig.4). The high density area (2.3km?) con- tained 4.20x10° scallops while the low density area (1.6km?) contained c.0.06x10* scallops (Table 2). The bed occupied 3.7km?, and interpolation among. the most external transects containing scallops indicated that the bed contained 3.66x 105 scallops.

This exercise was repeated at Honeymoon Bay where 20 transects contained scallops (Fig.5). The average number of scallops per m* in all transects with scallops was 0.130 (SE = +0.039). Plotting the location and density for each transect defined the boundaries of this bed (Fig.6). The high density area (70. 1scal/m?) was almost com- pletely surrounded by a low density area («0.1scal/m?), The high density area (2.3km?) contained 0,6] x 105 scallops (Table 2). The total area of 6.0km? contained approximately 0.78 x 106 scallops.

Tesi redimi annes Bl 220 » 10" оре ES) бё e 10 Scallups

TABLE 2. Mean of scallop density and estimation of abundance at 2 locations in Jervis Bay during April 1992, Abundance estimates were calculated using only those transects containing scallops.

Ау.

су ra a — — l [Density/transect| 0.991 | 1.538 | 0.443 | 0264 | 23 | 37 | 366 | | highdensiy | 1.865 | 2.633 | 1.097 | 0.349 | | tow density | 0036 | 0049 | 0.023 | 0.006 | 11 | L6 | 0% |

95% confidence limit

St | No. | Est. | Abun | error of areg dance | Upper | Lower Tran | (km )| (x10 ) sects

Murrays Beach

Honeymoon Ba

[0449 | 0097 | 0034 | 8 [23 | osi |

0.78

POPULATION BIOLOGY, P, FUMATUS, JERVIS BAY

Density [ EP È <0.1зср\/л© О Noscallaps

j af leny l

! /

17 23 m 2 + Won О a o’ Honeymocn Bay

} ГА | ale oS ) 3

EZ? [pira PU м о air

‚лә Ө? je.

0 5

La

km

—

FIG.5. Location of all transects at Honeymoon Bay. Figures on the circles are the transect numbers in April 1992,

SIZE STRUCTURE:The population size composi- tion and progression of the modal size classes (Fig.7) illustrate variations in size composition through time. At least two size classes were evi- dent in most samples. The number of scallops increased in the last six samples and the highest numbers of small scallops were also taken near the end of the investigation.

The first recruitment observed during this study occurred in November 1989 when two cohorts were observed; one with a mode in the 28mm class-size and a second in the 63mm class-size. On the basis of Hamer's (1987) ageing criteria, the first cohort could represent a 0+ age group and the second a mixture of 1+ and 2+ age groups. The two cohort structure seen in November 1989 and January 1990 persist until May 1990. From July 1990 to September 1990, the population size distribution was unimodal with no cohort com- ponents.

A second recruitment pulse appeared in November 1990. A few individuals of 28mm (0+ year of age class) suggest a small recruitment, or less than that of the corresponding month in the

251

previous year (November 1989). The sample from January 1991 showed the 0+ age group seen in November 1990 at 43mm.

The sample from March 1991 showed 2 size groups similar to those observed in November, 1989. This suggests that the main recruitment in the second year of this study occurred 4 months later than in the previous season. From March to May 1991, the two cohorts were evident, but they merged again by July 1991.

Small scallops are hard to see, and only one sample (March, 1991) had any individuals <10mm in shell length. Scallops «20mm shell length were also found in few samples (Novem- ber, 1989, January, 1990, March and May, 1991). The collection of small individuals coincided with estimated recruitment times. Small scallops were collected from around the bases of seaweed, arborescent polychaetes and sponges. Medium and large individuals were more conspicuous as they were only partly buried in the sandy sedi- ment. They shared the substratum with poly- chaete hummocks but were not always near the base of emergent benthic organisms.

Differences. in recruitment from one year to

Estimated Abundance B оо my Scallops E] ux ur Scallops

\

Montagu Pt. lg, Mu?

E

a lem I

)

/ Honeymoon Boy i /

FIG.6. Arcas of differential abundance of the commer- cial scallops at Honeymoon Bay in April 1992.

252

d ж

y | Maz, 9 dii x

g > g a E! F g шщ

Sues s386

a

Shell Length (mm)

FIG.7. Length-frequency histograms for Jervis Bay commercial scallops from September 1989 to July 1991, Class-size interval

= 5mm.

another like those observed for the commercial scallop in Jervis Bay (Table 3), are typical of scallop species and appear to be influenced by changes in oceanographic conditions such as temperature and nutrient availability. Settlement and post settlement conditions in 1989 may not have been the same as in 1990 or 1991.

MEMOIRS OF THE QUEENSLAND MUSEUM

BIOLOGICAL STUDIES

REPRODUCTIVE CYCLE:

Gonosomatic index (GSI): Two periods of low GSI were December 1989 to March 1990 and November 1990 to March 1991 (Fig.8). Four peaks occurred in the 1989/90 cycle (August to Septem- ber, mid-November, mid-April to mid- May and after mid-July), and four during the 1990/91 cycle (mid-August, late Oc- tober, late April and mid-May). In both years, each peak was followed by a decrease in GSI, which may correspond to a partial spawning event, Jacobs (1983) described a similar situation, with at least 3 spawning peaks in Jervis Bay: late winter to early spring, early summer and late autumn. The reproductive cycle of P. fumatus in Port Phillip Bay (Sause et al.,1987a,b) showed a similar pattern with some gamete release taking place in winter and a major release in late spring, Regional differences in spawning be- haviour may exist among P. fumatus populations in South Australia, eastern Victoria, southern New South Wales and Tasmania.

Parasitised gonads were present in every sample (Fig. 9), although the fre- quency increased from January to June 1990 and from November 1990 to March 1991. There was no obvious temporal pat- tern in the occurrence of parasitised gonads, but the mean frequency of occur- rence from August 1990 to July 1990 was higher than the similar period in the year 1989-1990, The degree of infestation may be indicated by the orange and red in the parasitised gonads. An orange gonad could be the early stage of infestation in which animals are still reproductive. A red gonad could be a final stage of infes- tation resulting in total loss of reproduc- tive capacity.

Many exogenous factors influence reproduction in scallops, but temperature and food are most important (Macdonald & Thompson,1986; Barber & Blake,1991). The annual average bottom temperature (18.17°C from August 1989 to July 1990 and 19.02°С from August 1990 to July 1991) were significantly different when compared in an ANOVA (df=1, MSE=18.60, F=16.18, P>0.0001).

Temperature data were correlated with GSI and

POPULATION BIOLOGY, P. FUMATUS, JERVIS BAY

Year 1989-1990

15 Year 1990-1991

A SO ND J'F'MA'M]']J FIG.8, Commercial Scallops gonadosomatic index (081) from August to July in two consecutive years in Jervis Bay.

frequency of parasitised scallops. Temperature has been positively correlated with GSI in other species (Paulet & Boucher,1991), but in this study such a correlation was not clear. During the first year, the correlation coefficients between bottom temperature and GSI have negative values and are not significantly different over lags of up to 3 previous weeks. In the second year, such correlations are not significant. The correla- tion coefficients between bottom temperature and the frequency of parasitised scallops are not sig- nificant in the first year, but in the second year, the correlation coefficients are significant over lags of up to 3 weeks.

Bottom temperature did not seem 1o have a direct influence on GSI, however, the positive correlation between temperature and frequency of parasitised scallops may be a factor that reduces the reproductive capacity of the scallop

TABLE 3. Comparison between settlement on collec- tors and recruitment of the commercial scallop in Jervis Bay.

NT 1989-1990 | Recr- | 1990-1991 | Recr- | uitment SE nitent | 199]

Ee | Oct-Dec | peos — 79.89 oS | [249 |

ET зз ва

| Dec-Feb | Feb

асаа Ба (Scal/m )

253

Cw (qw 19900 e оя {үнүн

теңине of parawitised (55)

Мим

FIG.9, Percent frequency of parasitized scallops in Jervis Bay during the sampling period from August 1989 to July 1991.

population by increasing the number of infertile individuals. A year of low temperatures followed by one or more of high temperatures (such as the period August 1989 to July 1991) could reduce recruitment in subsequent years.

Macroscopic staging: The majority of gonads in all samples were in the Developing 2 or Spawning 1 stages (Fig.10). The Developing 2 stage made up >40% of the samples in October and May of both years and September and December of 19%), The second most common stage, Spawning 1, peaked between February and March, June, August and November of 1990 and in March 1991, The number of ripe gonads peaked in November 1989 and April 1991 but smaller peaks occurred throughout the year, Spawning 2 gonads peaked in late August of 1990, showed smaller peaks in the previous January and June, and showed no strong peaks in the second year of sampling. In the first year, there was a greater percentage of gonads in spawning condition (Spawning 1 and Spawning 2 stages) than in the second year. In the second year, there were more developing gonads (Developing 1 and Develop- ing 2 stages) and ripe gonads,

Observer expérience is needed to make correct classifications and determine macroscopic stages. For example, differences in gonad thick- ness between Developing 1 and Developing 2 stages, and differences in the turgor of Ripe and Spawning 1 gonads are determined subjectivelv. Presence of the alimentary loop and its visual characteristics are also subjectively determined. The colour and outline of the loop depends on the type and amount of food eaten and the position of the loop within the gonad. Sometimes the loop

254

Developing 1

vn Developing 2

Ln

wa = T

ми т Ripe a 400 a Stp ay: и.

Spawning 1

Spawning 2

FIG.10. Percent frequency of macroscopic stages for com- mercial scallops from Jervis Bay during October 1989 to July 1991. Figures on the bottom are days of sampling.

may be pushed towards one wall of the gonad as the gonad ripens. After almost complete spawn- ing (Spawning 2), some gonads retain fluid so the gut loop may be invisible.

Microscopic staging: No specimens were in the Immature or Early Development stages as the samples contained only adults. All other micro- scopic stages were present most of the year (Fig.11), Developing, ripe and resorbing scallops occurred in 11 of 12 months with peaks in May, April and July, and April and May respectively, The Partial Spawning stage was present in all 12 months with a peak between February and March and the Extended Spawning stage was found in 9 of the 12 months. Resting gonads were present during summer (December, January, February) and winter (June, July, August). Resting gonads were most numerous in December and June. The Partial Spawning stage occurred every month, the Resorption stage occurred in all

MEMOIRS OF THE QUEENSLAND MUSEUM

months except one, and the Extended Spawn- ing stage was not numerous. Therefore, the commercial scallop in Jervis Bay spawns a number of times during the breeding season. Tt seems unlikely that complete spawning with an entire release of gametes occurred in Jervis Bay.

Histologic examination of gonads is im- portant to confirm spawning, as a drop in the gonadosomatic index (GSI) may indicate resorption. If resorption is high, fecundity estimates are not related to the numbers of viable eggs released (Tremblay,1988), The area of the gonad is also important in analysis because a previous test (Fuentes et al., 1992) showed that the fore region of the female part had significantly more oocytes per follicle than either the mid or tip regions. Further- more, histological sections often showed an ‘edge effect’, i.c., the follicles had collapsed at the edges of the section and the oocytes were dislodged from the follicle walls. Con- sequently, gonads were only compared by taking sections from the same region of the gonads and making classification on the centres of the sections.

The finding that the Jervis Bay commercial scallops have extended dribble spawning is not unusual, In other species of scallops, ma- ture gonads are present all year (Paulet et al., 1988) and partial spawning or more exten- sive spawning can occur in any month of the year (Coe,1945), Paulet et al. (1988) sug- gested that dribble spawning could be an adaptation to an unpredictable environment. The hypothesis is that at least some larvae will find favourable conditions and the chances of cither very weak or very strong recruitment are minimised (Paulet et al., 1988).

Comparison of macro- and microscopic staging schemes: Classifications derived (сот macro- scopic and microscopic staging were compared to determine whether a simpler technique would allow an accurate prediction of scallop reproduc- tive behaviour. When the macroscopic and microscopic techniques were compared, the macroscopic stages Developing 1, Developing 2, Ripe, Spawning | and Spawning 2 were assumed to correspond with microscopic stages Early Development, Developing, Ripe, Partial Spawn- ing and Extensive Spawning, respectively. The comparison gave a poor result, for example macroscopic staging consistently overestimated the condition of developing scallops (Fig,!2), The accuracy of the macroscopic technique was

POPULATION BIOLOGY, P. FUMATUS, JERVIS BAY

LU

do Developing

x)

E

1" ы %

ы

3 "

4n Ripe

30

E

10 | 0 ü

ц Pattial Spawning

Extended Spawning

Relative Abundance (%)

Resorptión

Resting

а з 19 „ y

Nov Dec Jan Feb Mar Apr May jun Jul Aud Sep Ort

FIG.11. Relative abundance (%) of microscopic stages for commercial scallops from Jervis Bay. No specimens were in Immature or Early Devclopment stages.

correct only с.509% of the time when classifying Ripe and Spawning scallops, with no consistency between the degree of over- or underestimation of gonad stage.

The lack of correspondence can only be partly explained. For example: some scallops gave the macroscopic appearance of being in Spawning 1 stage, but key histological features meant they were placed in the microscopic Resorption stage. ]t was not possible to macroscopically classify scallops as being in either the Resorption or Rest- ing stage. For similar reasons, scallops appearing to be in the macroscopic Spawning 2 stage could have been in the Resorption or Resting stages. Another problem may have occurred when the loop of the alimentary canal was visible and the gonad was therefore classified in the Developing 2 stage, but the gonad would be classified as Ripe when viewed microscopically. When a gonad displayed orange spots it was allocated to Spawn- ing 1 stage. However, if the section did not en- compass the spotted area, the gonad would be

255

25

E OVERESTIMATED 80 EQUIVALENCE UNDERESTIMATED

CORRESPONDENCE ("53 а

Davi/ED

Day?/Dey Ripe/Ripe S 1/PS 5 2/ЕМ З STAGE

FIG.12, Correspondence between macro- and micro- scopic stages. DEV. 1=Developing 1; E.D.=Early Development; DEV.2=Developing 2; DEV .=Developing; S.]-Spawning 1; P.S.=Spawn- ing 1; $.2=Spawning 2; EXT.S.=Extended Spawn- ing.

classified as Ripe when viewed under the micro- scope, The first three of the scenarios above lead to an underestimation of gonad stage; the fourth leads to an overestimation.

Macroscopic and microscopic staging schemes have their own sets of advantages and disad- vantages, Macroscopic staging is imperative where the animals cannot be sacrificed, and its relatively few stages are suitable for a rough classification of gonads while in the field or under hatchery conditions. However, the macroscopic scheme depends very much on the observer's ability to make correct classifications, e.g., scal- lops classified in Spawning 1 or Spawning 2 stages might really be in Resorption or Resting stages. The primary advantage of the microscopic scheme is that it provides a more accurate under- standing of an individual animal’s condition, but a lengthy period of time is required to prepare and process histological material. As Jervis Bay scal- lops do not appear to have a well defined repro- ductive cycle and they appear to dribble spawn, provision might need to be made for microscopic staging to follow their reproductive development during recovery of the population.

SETTLEMENT

Two studies were aimed at the spatial and tem- poral characteristics of scallop settlement in Jer- vis Bay. The first study, carried out on the two scallop beds assessed the magnitude, depth stratification and seasonality of settlement. The second study of 5 locations, initiated in Septem- ber 1990 and finished in February 1991, ad-

256

Ш] ——— Murrays Beach

A Honeymearr Нау

Meso Scallpps/ Dag

Month

FIG.13. Mean and standard error of the number of commercial scallop spat settled by month at two locations in Jervis Bay (Oct 1989 - Oct 1990.

dressed the question of larval dispersion within the bay and allowed comparison of settlement between years.

In the first study, settlement data was analysed by time, location, zone and site according to the design described in Fuentes et al. (1992). Sig- nificant temporal variability was found in the

TABLE 4. Summary of analysis of variance (ANOVA) of scallop spat settlement at 2 locations, 2 zones and 3 sites over time at Jervis Bay. *0.01- р>0.001; **0.0012p20.0001; ***p=0.0001; ns=no significance.

[Source of variation — | ar | SS |F value | Sgnit. | | Location [1]ил4] 532 | ns | Zoe — — 11 1123011 1230 |. n | Location*Zone — [1 [4850 | 220 | ms | [Sie(LocaionZone | 6 | 13.212 | 1139 | *** | hue — Е И 777771771 ЕГШ [Location*Time — |s [133.110] 14.65 | we _ Zone*Time | 8 | 17.640 |

[om | [Time*Site(Loc*Zone | 34 | 38.619 | 588 | +* | [Lscation*Zover Time | 8 [12237] 195 | ш] [Den — 5 0 0 [s

7.704 5.16 ** LEER [c [ss Гаа | se ZoneDep [5] 4.323 mere — [ao fase | zs ШЕГШ Vies kal Location*Zone)

[Residual — — — [srz|iseoed] | — |

MEMOIRS OF THE QUEENSLAND MUSEUM

и —=— Ммитгү Бакі Ёле! — Honeyman Day Zone 1 —©— Митака Zone? = Honeymoon Bay Zone?

Mean Scallops bay,

Depth (mi

FIG.14. Mean and standard error of the number of scallop spat settled by depth stata, zone and site.

mean number of spat that settled on the ex- perimental longlines (Table 4). Maximum settle- ment was recorded from November to January (Fig.13). At both locations, settlement was mini- mal from February to June, but increased after July. Different temporal pattern in settlement were observed at Murrays Beach and Honey- moon Bay. It appeared that the duration of settle- ment was similar at both locations, but peak settlement seemed to occur two months earlier at Murrays Beach. The time of maximum larval abundance varies within P. fumatus (Young & Martin,1989). In Tasmanian waters between King Island and Banks Strait, similar temporal differences in settlement were found from one location to another, within the same location (Young et al., 1988), and from one year to the next (Hortle & Cropp,1987). Settlement begins in September (Young & Martin,1989) and con- tinues to December, but at decreasing intensities, in southern Tasmania (Hortle & Cropp, 1987). In eastern Bass Strait, settlement occurs November- December (Hortle,1983; Young et al., 1988). Differences in settlement at the first two spatial scales (location and zone) were not significant, but the differences among sites (within zone and location), were significant, suggesting small scale patchiness in settlement of P. fumatus in Jervis Bay. Spatial variability in settlement of P. fumatus has been documented in Port Phillip Bay; differences were observed in the number of set- tling spat at sites only 30km apart (Gwyther et 31,1985; Sause et 31.,1987b; Coleman, 1988).

POPULATION BIOLOGY, P, FUMATUS, JERVIS BAY

El (инт kd [алеу

Mean scallope/bag

теа аном Нир CREE lOS I HONITMOON. OWT mw

Location

FIG.15, Mean and standard error of the number of scallop spat settled from December 1990 to February 1991 by location and time.

Similar variability occurs in Bass Strait in areas separated by larges distances (Young et al., 1992),

Mean numbers of spat that settled at different depth strata were significantly different, The highest settlement in Zone 1 (14m) was in the 8—12m Depth strata and in Zone 2 (18m) settle- ment was greatest at 8-14m (Fig. 14), The lowest settlement was at the 4m depth stratum. Hortle & Cropp (1987) found that fewer spat settled near the surface and near the seabed (10-20m in a depth of 31m) in Mercury Passage on the east coast of Tasmania. Young et al. (1988,1992) reported that larvae tended to settle on collectors

laced near the bottom rather than on those higher in the water column off northern Tasmania, A combination of water temperature (thermal stratification), with factors such as larval be- haviour, could also influence settlement in Jervis Bay. Jervis Bay has a strong thermal stratification most of the year (Holloway etal.,1989,1990) and P. fumatüs settlement, like that of other species (Mileikovsky,1973; Mann & Wolf,1983; Trem- blay & Sinclair, 1988), may be influenced by such stratification.

In the second study (September,1990 to February, 1991) settlement was observed in cach of the five locations where longlines were placed (Fig.15). Significant spatial and temporal variability was found in the mean number of spat that settled on collector bags with variation oc- curing among the five locations, among the three times and between the two sites within each loca- tion. Comparisons of settlement at different depths show similarities to results of the first study: settlement was lower on collector bags placed near the surface than on those placed near

25]

Mean sell ps (bag

COP PONVT

MURKA yS

VLANT ANON есм HEACH ммт

Mop MOV WAY

масла!

FIG.16. Mean and standard error of the number of scallop spat settled from December 1990 to February 1991 by location and site.

the bottom. Comparisons indicated higher settle- ment at Murrays Beach and Honeymoon Bay (outer Bay) than at the other three locations (inner Bay). The temporal variations in this second study were similar to those in the first i.e. highest in Deceniber (Fig.16). However, in this year there were no differences in the timing of settlement between Murrays Beach and Honeymoon Bay.

It has been postulated that the larvae of P. fumatus may nol disperse widely from the adult population and that the number of larvae reaching the pediveliger stage may be related to the size of the nearby adult populations (Mason,1983; Young et 31,1988). In Jervis Bay, there were differences between years in the mean number of spat that settled on collectors. More spat were observed in December 1990 than in December 1989 at both locations, The average number that settled pr collector was higher at Murrays Beach probably because the abundance in the nearby population is higher than in Honeymoon Bay. Whether successful settlement in Jervis Bay is related to the proximity or size of the adult population is still to be demonstrated.

The low densities of the adult populations at Murrays Beach and Honeymoon Bay could be the reason for the low settlement during the study period. The settlement figures (average of 35 scallops/collector bag in November 1989 at Mur- rays Beach and 15 scallops/collector bag in January 1990 at Honeymoon Bay) are less than the average of 89 scallops/collector bag reported in 1982 off Huskisson (Jacobs,1983). Further- more, figures for Jervis Bay are much lower than figures reported for eastern Tasmania (516 scal- lops/collector bag in 1982/83, 425 scallops/col-

258

lector bag in 1984/85 and 325 scallops/collector bag in 1985/86, Hortle & Cropp, 1987) and for Port Phillip Bay (Sause et al., 1987b),

From these two studies, it js concluded thal scallop larvae were distributed around the hay and that there were limitations on settlement at areas other than the two main beds. One implica- lion of this conclussion is that changes which inhibit settlement may have occurred in the habitat at some sites, This might be the reason why commercial scallops disappeared from areas they were abundant in the previous decade. A second implication derived from this study ts that the presence of larvae in the water column, the timing of spat settlement and the variation in settlement with depth are relevant factors in the design of systeins for the collection of wild spat.

The magnitude, stratification and timing of lar- val settlement and dispersion are important management issues for commercial scallop fisheries, Attempts have been made to relate P, fumatus settlement in one year to recruitment in subsequent years [Sause et al., 1987b; Gwyther & Burgess,1987, Coleman, 1988; Coleman & Gwyther, 1988). Coleman (1988) found that suc- cessful settlement may not necessarily mean good subsequent recruitment. However, in this study differences in settlement were evident and they coincide with a greater adult densities recruitment observed in the Murrays Beach and Hone Bay beds in the transect surveys in

ACKNOWLEDGEMENTS

Thanks are due to L. Diver and A. Smith for their technical assistance during the study and to R. Williams for comment on the manuscript and constant encouragement. Thanks to E. Ortiz for assistance with the statistical analysis. Thanks are also due to an anonymus referee and to M. Dredge for critically reading the manuscript. | thank the CSIRO Jervis Bay Marine Station for providing the temperature data,

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STEWARD, P., KAILOLA, P.P. & RAMIREZ, С, 1991. Twenty-five years of Australian fisheries statistics. Bureau of Rural Resources, Cariberra, Working Paper WP/14/91,

TREMBLAY, M.J. 1988. A summary of the Proceed- ings of the Halifax sea scallop workshop, August 13—14, 1987. Canadian Technical Report on Fisheries and Aquatic Science 1605: 1— 12.

TREMBLAY, J.M. & SINCLAIR, M. 1988. The vert; cal and horizontal distribution of sea scallap (Placopecren magellanicus) larvae in the Bay of Fundy in 1984 and 1985. Journal of Northwestern Atlantic Fisheries Science В: 43-53.

WILLIAMS, RJ. & DIVER, L.P. 1988. Commercial molluses of Jervis Bay. Pp. 163-197. In ‘Jervis Bay Marine Ecological Studies. First Interim Report'. (Fisheries Research Institute, NSW Agriculture and Fisheries: Cronulla).

YOUNG, P.C., MARTIN, R.B., MCLOUGHLIN, RJ. & WEST, С. 1988. Variability in spatfall and recruitment of commercial scallops (Pecten fumatus) in Bass Strait, Pp.80-81. In Dredge, M.L.C., Zacharin, W.F., & Joll, L.M., (eds), ‘Proceedings of the Australian Scallop Workshop, Hobart'. (Tasmanian Government Printer: Hobart).

YOUNG, P.C. & MARTIN, R. 1989. The scallop fisheries of Australia and their management. Aquatic Science 1(4): 615-638.

YOUNG, Р.С, MCLOUGHLIN, R.J. & MARTIN, R.B. 1992, Scallop (Pecren fuumarus) settlement in Bass Strait, Australia. Journal of Shelfish Re- search 11(2): 315—223,

UNUSUALLY HIGH RECRUITMENT IN THE SHARK BAY SAUCER SCALLOP

(AMUSIUM BALLOT) FISHERY L.M. JOLL

Joll, L,M, 1994 08 10: Unusually high recruitment in the Shark Bay saucer scallop (Amwusium аца) Пен; Memoirs of the Queensland Museum 36(2) 261-267, Brisbane, ISSN 79-8835.

From 1983, when the Shark Bay scallop fishery reached full exploitation, to 1990, the largest annual catch had been 731 tonnes (meat weight) in 1988. In 1991 and 1992 catches of 2,532 and 4,144 tonnes, respectively, were taken, The increased catch in 199] was attained despile total effort being the second lowest on record, while catch per unit effort (CPUE) was the highest on record. Total effort in 1992 increased considerably and was the highest on record, while CPUE was second only to that achieved in 1991. The very high catches and CPUEs were the result of a massive increase in the recruitment of juveniles derived from the 1990 breeding season. Annual stock surveys showed recruitment indices in some areas of Shark Bay up to six times higher than the previous record. Juveniles recruited in 1990 formed the bulk of the fishable stock in 1991, but the available effort in the fishery was unable to take all the fishable stock in 199] and the 1992 catch was composed mostly of residual animals carried over from the 1991 season, High recruitment into the Shark Bay saucer scallop fishery is usually associated with low mean sea levels (2 weak Leeuwin Current) over the winter (spawning) months. A chance association of spawning with an additional hydrological or other environmental event favourable to larval retention or survival may have multiplied the effect of a weak Leeuwin Current.

L.M. Joli, Bernard Bowen Fisheries Research Institute, Western Australian Marine Research

Laboratories, Р.О, Box 20, North Beach, Western Australia 6020; 9 March 1994,

The fishery for saucer scallops (Amusium bal- loti Bernardi, 1861) in Shark Bay has been fully exploited since 1983; its catch depends on recruitment from the breeding season of the pre- vious year (Joll & Caputi, in press). Surveys of recruit (0+) and residual (1+ and older) scallops at the start of cach season showed recruitment from the 1990 breeding season as the highest recorded. As a result of the very high recruitment, the 199] catch was approximately three times higher than the previous record catch. However. despite the high catch in 1991, there were still large numbers of scallops at the end of the 1991 season. These formed the basis of the 1992 fishery, which took a catch over 50% greater than the record 1991 catch. Joll & Caputi (in press) have shown that thesc high levels of recruitment are associated with low mean sea levels, which reflect periods of a weak Lecuwin Current. This paper examines the background to the high 1990 recruitment and documents features of The even] for use in population dynamics studies.

MATERIALS AND METHODS

Scallops are caught by vessels which are licenced to fish only for scallops (using 25.6m [14fm] headrope length nets of 100mm mesh)

and vessels which fish for prawns and scallops (using (29,3m [16fm] nets of 50mm mesh) (J01l,1987,19392), Catch and effort data are ob- tained from a voluntary logbook system com- pleted by all vessels in both sectors of the fishery, and caich data are cross-checked with recetval records of wholesale buyers. Catch per unit effort (CPUE) data were derived from the catch and effort of the scallop fleet. Effort of prawn/scallop vessels may be directed at either prawns or scal- lops or a combination of the two. To determine à standardised effort value for the prawn/scallop fleet equivalent to the effort of the scallop fleet, the catch of the prawn/scallop fleet was divided by the CPUE of the scallop fleet. Total effort was calculated as the sum of the effort of the scallop fleet and the standardised effort of the prawn/scallop fleet.

Surveys of scallop abundance have been con. ducted in November cach year since 1983, at the end of the scallop and prawn fishing seasons and near the end of the breeding season, using the 20m twin-rigged research vessel ‘Flinders’, A standardised pattem of survey trawls is carried out, using twin 50mm mesh trawls of 22,0m (12fm) total head rope length, to determine the abundance of scallops in the areas of the bay where the fishery Operates. Scallops caught in

262

4000-

3000

n3 [m] e e

LANDINGS (tonnes meat) © S

87

MEMOIRS OF THE QUEENSLAND MUSEUM

30000

20000

10000

TOTAL EFFORT (hrs.)

88

YEAR

FIG. L.Scallop catchs (tonnes meat) from Shark Bay, 1983-1992 (stippled bars) and estimated total effort (+).

each survey trawl are separated, primarily on the basis of size, into recruits (0+ animals derived from the breeding season commenced in April that year (Joll,1987)) and residuals (1+ and older animals) and the numbers of each category recorded. Most recruits are less than 75 mm in most years and most residuals are larger than 75mm. However, when size overlaps occur, the recruits and residuals can still be separated on the pattern of the daily growth rings on the coloured left valve (Joll, 1988), with recruits showing widely spaced rings over the whole surface of the left valve while residuals have a zone of highly compacted rings near the valve margin.

Survey trawls are normally of 20 minutes dura- tion and с.і nautical mile long, although in areas of high abundance shorter trawl durations and distances are used. The distance covered by each survey trawl is determined either by radar fixes (1983-1989) or from global positioning system readings (1990 onwards) and, using the time taken for the trawl, the average speed of the trawl is determined. Catches of scallops are adjusted to catches per nautical mile, while the effect of speed on catchability is partially compensated for by applying factors determined by Penn (unpub.) for the catchability of adult (=residual-size) scal- lops relative to an arbitrary speed of 3.4kt. Survey

data for each trawl shot are ultimately expressed as the catch of scallops per nautical mile (spnm) at 3.4kt for 12fm of head rope. The adjustment for the effect of speed on catchability does not compensate for the differences in catchability of recruit and residual-sized scallops and the indices for these two categories cannot be compared directly. However, the data allow for year-to-year comparisons within the categories.

Abundance indices of scallops on the main grounds (Shark Вау N of 25° 30'S) and the smaller ground in Denham Sound are derived from survey data as the mean abundance of recruits and residuals in the survey shots. The main grounds are further sub-divided into north- ern (N of 25° 10'S) and southern (S of 25° 10'S) sub-areas. Because the main grounds have con- tributed the bulk of the catch in most years, pre- vious work (Joll & Caputi, in press) has concentrated on the relationship between an en- vironmental factor (Leeuwin Current strength) and the index of abundance of recruits on the main grounds. The survey data have also been used to examine the relationship between index of abundance of recruits and residuals on the main grounds and catch from these grounds in the following year. However, recruitment in 1990 also gave rise to a significant catch from the

HIGH RECRUITMENT IN SHARK BAY SAUCER SCALLOP

TABLE 1. Abundance indices of scallops from various sub-areas in Shark Bay from surveys in November 1983-92 (data are spnm for 12 ftm of net towed at 3.4 kts), REC.=recruits; RES.=residuals.

|| MAINGROUNDS _| DENHAM SD. |

[1958 | sa | 73 | & | 7 | 33 |o] [185 | i343 | 92 [227 | 2 [30 | os | [1985 | 277 | 47 | 75 | 03 | э | 07] [1987 | sos | 133 | 609 | as | 32 | 7 | [ 1988 | | 2 2 | [19 | o2 | as [ r9 | 2 | 32 | v | [1990 | eo | 77 [356 | 73 | & | a | [1991 | 169 | 2411 | so |4253 | 100 | saa | [1992 | 162 | то | 157 | 467 | зві | 439 |

Denham Sound grounds and data relating Leeuwin Current strength to recruit abundance and catch on the Denham Sound grounds are also presented.

Strength of the Leeuwin Current, flowing S along the Western Australian coast during the austral winter, is reflected in coastal sea levels (Reid & Mantyla, 1976; Pearce & Phillips, 1988). The major spawning activity of A. balloti in Shark Bay occurs between April and July (Joll & Caputi, in press) and it is the strength of the current in these months which is most relevant, Unfortunately, sca level data are not available for the Shark Bay area for all of the relevant period, but the available data shows that changes in sea level at Carnarvon (25°, | 14" E) are reflected in sea level data from Fremantle (32°S, 116°E) one month later {Joll & Caputi, in press). As an index of Leeuwin Current strength in the Shark Bay area in April to July, the mean value of the sea level at Fremantle, lagged опе month (1.6. May lo August), was used,

RESULTS

CATCH AND EFFORT

Total scallop catch from Shark Bay by all ves- sels licenced ranged from 121 tonnes ta 731 tonnes between 1983-1990, with a mean of 432tonnes/year (Fig.1). Catches for 199] and 1992 were 2,532 and 4,144 tonnes respectively. The increase in catch in 1991 occurred despite total effort being the second lowest on record, while catch per unit effort (CPUE) of the scallop fleet was the highest on record at 200.2 kg h”,

more than 5 times higher than the previous highest CPUE. The low effort figure for the 1991 season was a consequence of processing limita- tions on the fishing vessels, with vesscls only fishing for a few hours each day and spending the remainder of the day processing the catch. The effort in the 1992 season was the highest on record, partly as a result of a large increase in effort hy the prawn/scallop fleet, but the CPUE of the scallop fleet of 137.9 kg h! was second only to the 1991 figure and nearly 4 times greater than the previous highest CPUE recorded.

Survey Data

There was a very high abundance of recruits in November 1990, with an exceptionally high abundance in the southern sub-area of the main grounds - over 6 times higher than any of the previous indices determined for any sub-area of Shark Bay (Table 1). Moreover, despite a high 199] catch, residual scallops in November 1991 were exceptionally abundant in the southern sub- area and high in the other sub-areas, These high abundances of residual scallops came about be- cause, unlike years in which recruitment was al a more normal level, the effort of the scallop and prawn/scallop fleets could not fully exploit the 1991 recruitment, Another very large catch was. taken in 1992, based primarily on the residual scallops detected in the 1991 survey, which were derived from the 1990 recruitment. By November 1992 the abundance of residual scallops had decreased considerably, reflecting the impact of the fishing activities of the fleets in the 1992 season, when recruitment to the fishery was close tọ normal.

Recruitment levels for 1990, categorized into 3 abundance classes (Fig. 2А), show that recruit- ment was not uniform through the sub-areas. The principal area of recruitment was in the southern sub-arca of the main grounds, with a core of very high abundance (5,000 spnm) surrounded by an area of relatively high abundance (1,000-4,999 spnm). Residual scallop abundance in the 1991 survey (Fig. 2B) reflected fairly closely the dis- tribution of recruits in the 1990 survey, with the exception of a small area of high abundance of residual scallops in the northem arca. The ap- parent emergence of this area of residual scallops in November 1992 may indicate that recruitment in the northern sub-area occurred slightly later and was not measured fully by the November 199] survey,

The highest recorded catches (12fm net at 3.4kts) in the 1990 and 1991 surveys were 19,075

264

10'

20'

30'

40'

113? ш 20 307 40!

Number / nautical mile: * 0-999

e 1000—4999 6 5000 +

MEMOIRS OF THE QUEENSLAND MUSEUM

Number / nautical mile:

0-999 œ 1000—4999 65000 +

FIG. 2. Distribution of the abundance of scallops in Shark Bay recorded in surveys in November.

A, Recruits, 1990. B, Residuals,1991.

recruit spnm in 1990 and 59,242 residual spnm in 1991. Conversion of these catch rates to abundan- ces requires application of catchability factors relevant to the various trawl speeds. Joll & Penn (1990) showed that the catchability of residual- size scallops at a speed of 2.5 kt is approximately 0.6, while the adjustment of this catchability fac- tor to the higher trawl speed of 3.4kt at which the survey data are expressed is also 0.6 (Penn un- publ. data). Application of these catchability fac- tors to the 1991 figure for the highest catch of residual scallops equates to an actual abundance of 164,561 spnm in the path of the trawl. Assum- ing a trawl path of 60% of the headrope length of

trawl used (Joll & Penn,1990), the area swept in a 1 nautical mile trawl would be 24,446 m*. On this basis density of adult scallops in the shot with the highest abundance of residual scallops in the 1991 survey was estimated to be 6.7 scallops тг. The catchability of recruit scallops has not yet been formally determined. However, based on the lower swimming capacities of smaller scal- lops and the increased latency of their response to a stimulus to swim (Joll 1989b), it could be expected that the catchability of recruit-sized (50- 60mm) scallops would be about 30-40% of that of residual-size scallops. On the basis that the catchability of recruit-size scallops is 40% of that

HIGH RECRUITMENT IN SHARK BAY SAUCER SCALLOP

77 78 79 80 81 82 яз B4 B5 86 87 BB

SEA LEVEL (MAY — AUGUST)

73 74 75 76 77 78 79 80 ві 82 вз ва B5 86 87 вв SEA. LEVEL (MAY — AUGUST)

FIG. 3. Relationship between the index of recruit abundance (mean spnm) in Shark Bay and mean Fremantle sea level (cm) over the period May to August. A (bottom left), Main grounds. B, (upper right), Denham Sound.

of residual-size scallops, the density of recruit scallops in the path of the trawl with the highest catch of recruits in the 1991 survey was estimated at 5.4 scallops m”.

EFFECTS OF THE LEEUWIN CURRENT

The relationship between the recruitment index for the main grounds and mean Fremantle sea level over the period May to August in the period 1983 to 1992 (Fig. 3A) showsthat the recruitment index was highest in years when the mean sea level was low. Recruitment data for Denham Sound (Fig. 3B) show a high recruitment index in 1990, when sea level was low. However, in 1987 when sea level was similarly low, there was no increase in recruitment and in 1992, when sea level was not particularly low, there was also a high recruitment.

In most years there is a high level of exploita- tion of the scallops recruiting to the fishery, which gives rise to a strong correlation between the abundance index of recruits in one year and catch on the main grounds in the following year and between sea-level in one year and catch on the main grounds the following year (Joll & Caputi, in press). However, because of the in- ability of the fleet to fully exploit the fishable stock available in 1991, there was a considerable

carry-over of scallops into 1992. This gave rise to a high catch in 1992 on both the main grounds and the Denham Sound grounds which was not related to the sea- level of the immediately pre- vious year (Fig. 4A,B). Although survey data showing recruitment strengths are not available prior to 1983, the inclusion of data for the 1983 catch and the 1982 sea level provide additional confirmation of a relationship between sea level and catch in the following year (except 1992) on both the main grounds and in Denham Sound.

DISCUSSION

The high 1990 recruitment led to massive 1991 and 1992 scallop catches. On a live weight basis, the 1992 catch of scallops was over 20,000 ton- nes, making it the second largest single species fishery in Australia in that year after greenback jack mackerel. The combined catch of scallops by the scallop and prawn/scallop fleets in 1991 and 1992 was a little less than twice the accumulated catch of the previous eight years. The mean CPUE in 1991 was approximately 18 times greater than the highest mean CPUE in the Queensland saucer scallop fishery 1976-1987 (Dredge, 1988). Using an estimated mean adduc-

$

8 E EBf

CATCH (tonnes)

500

75 76

73 74

* 90/91 350 "91/92 — 300 : 250 : 8 82/83 B — 200 B шо 100 50 D ^ 87/88 ^ 86/87 ^ 85/86

73

74

tor weight of 15g for scallops caught in 1991 and a mean of 20g for 1992, there were approximately 376 million scallops caught over 2 years. If most of these scallops had been caught in the year in which they recruited to the fishery, as is the case in years of more normal levels of recruitment (and without adjusting for the natural mortality of scal- lops from 1991 to 1992), an estimated catch of at least 5,500tonnes would have been taken in 1991.

Estimated densities of scallops in the area of highest abundance in the 1990 and 1991 surveys were as high as 6.7 scallops m. Higher densities of residual scallops than recruit scallops is probably a reflection of local variation in abun- dance, with slightly different areas trawled in

77 78 78 во в 82 аз 84 SEA LEVEL (MAY — AUGUST)

75 76 77 78 79 BO Bl 82 BS 84 85 88 87 88

SEA LEVEL (MAY — AUGUST)

FIG. 4. Relationship between total catch (tonnes meat) and mean Fremantle sea, level (cm) over the period May to August in the previous year. (86/87): (Year of sea level data/ Year of catch data). A (upper), Main grounds. B (lower), Denham Sound ( open circles represent ycars of no effort in Denham Sound).

MEMOIRS OF THE QUEENSLAND MUSEUM

different years. Alterna- tively, differences in catch- ability between recruit and residual-size scallops may have been underestimated, which would reduce the es- timated density of recruits.

Based on the minimum value of the upper category of abundances (Fig.2), this figure equates (on the same basis as previous estimates) to densities of 0.57 residual scallops m? and 1.42 re- cruit scallops т>. Dredge (1988) noted maximum density of Amusium balloti in Queensland at around Im~, while Joll & Penn (1990) reported densities of scallops of 0.08-0.09m* in an area of Shark Bay in 1986. The area occupied by scallops at an estimated average minimum density of 1.42 recruits m^ and 0.57 residuals m? in the 1990 and 199] surveys (based on the area enclosed

85 B6 87 88

суи by shots of 5,000 spnm or

greater) was around 90km?

* 89/90 and 60km? in the two years в8/89°° 84/85

respectively. Scallops at very high local densities and generally high den- sities across a wide area over a two year period indi- cate a capacity of the en- vironment to support large numbers of scallops without any apparent depletion of the food resources.

The mechanism by which the Leeuwin Current affects recruitment success in Shark Bay is not fully understood. Satellite imagery shows that, when the Leeuwin Current is near the coast off Shark Bay, bodies of warm Leeuwin Current water sometimes move away from the main flow of the current and enter Shark Bay (Joll & Caputi, in press). This may flush larvae out of the bay or into the saline embayments along the mainland shore line. Hydrological flushing has been recog- nised as factor affecting recruitment in Placopec- ten magellanicus and Pecten maximus (Dickie,1955; Caddy,1979,1989; Thouzeau &

HIGH RECRUITMENT IN SHARK BAY SAUCER SCALLOP

Lehay, 1988). Alternatively, the higher tempera- ture ог lower nutnent levels of the Leeuwin Cur- rent water (Pearce,1991) may provide an environment which is less suitahle for larvae.

The abundance pattern of 1990 (Fig. 2А) had a core of very high abundance surrounded by an area of relatively high abundance, suggesting thal larvae were contained within a well-defined eddy feature at settlement, Dredge (1988) suggested that a gyre in Hervey Bay in Queensland may act to trap larvae of А. ballot and Caddy (1979) hypothesized that recruitment to the Bay of Fundy scallop fishery was positively influenced by the degree of retention of larvae within a gyre. Greater retention of larvae within Shark Bay, perhaps inside clearly defined hydrographic fea- lures, appears to be the most likely cause of incre: larval survival and juvenile recruitment in years when the Leeuwin Current is weak,

The reason for disproportionately high recruit- ment in 1990, compared with that occurring at similar average sea level values in 1982 and 1987 isnotclear. There may have been some additional hydrological factor which led to ап unusually high level of larval retention within the bay or some other environmenial event which led to à high retention or survival rate of larvae. The action of an additional fayourable factor or fac- tors Within a low sea level environment already basically conducive to good larval survival may have been greatly heightened by the synchronisa- tion of that event with spawning activity, Amusium balloti is à multiple spawner (Joli, 1987,1989a) with a larval life of c.22 days (Rose et al., 1988). With a relatively short larval life it may be that recruitment success can bencfit from chance associations between spawning and short term environmental factors which are not reflected in the mean sea level, The very compact and unimodal size-frequency distribution of the 1990 recruits in the arcas of very high abundance suggests that the bulk of the recruits in these areas were derived from one spawning, Synchranisa- tion of an additional hydrological or other en- vironmental event with а period of spawning may have led to the levels of recruitment success observed in 1990,

LITERATURE CITED

CADDY, J.F. 1979. Long-term trends and evidence for production cycles in the Bay of Fundy seallop fishery. Rapports et Procés- Verbaux des Réunions de Conseil International pour L- Exploration de la Mer 175: 97-108

CADDY, LF. 1989, Recent developments in resennch

267

and management for wild stocks of bivalves and gastropods. Pp. 665—700. In J.F, Caddy, (ed), 'Marine invertebrate fisheries: their assessment and management’. (John Wiley and Sons: New Yor!

)

DICKIE, LM, 1955. Fluctuations in abundance of the giant scallop, Placopecten magellanicus (Gmelin), in the Digby area of the Bay of Fundy, Journal of Fisheries Research Board Canada 12: 797-857,

DREDGE, М.С. 1988 . Recruitment overfishing in а tropical scallop fishery. Journal of Shellfish Re- search 7; 233-239,

JOLL. L.M. 1987. The Shark Bay scallop fishery, Fisheries Department Western Australia, Fisheries Management Paper 11:1—123.

JOLL, LM, 1988, Daily growth rings in juvenile saucer scallops, Amusium ballon (Bernardi). Journal of Shellfish Research 7: 73-76,

JOLL, L.M, 19892. History, biology and management of Western Australian stocks of the saucer scallop Amusitm ballati. Pp. 30-41. In M.L.C. Dredge, W.F. Zacharin & L.M, Joll, (eds), ‘Proceedings of the Australasian Scallop Workshop, Hobart’. (Tasmanian Governnient Printer: Hobart),

JOLL, L.M, 1989b, Swimming behaviour of the saucer scallop Amusium ballot’ (Mollusca: Pectinidae). Marine Biology 102: 299-305.

JOLL, L.M, & САРТ, N, in press, Environmental influences on recruitment in the saucer scallop (Amusium balloti) fishery of Shark Bay. In ‘Procecdings of the Shelliish life histories and shell fishery models Symposium’. ICES Marine Sciences Symposia.

JOLL, L.M. & PENN, J.W. 1990, The application of high- resolution navigation systems to Leslie -De- Lury depletion experiments for the measurement of trawl efficiency under open-sea conditions. Fisheries Research 9: 41—55,

PEARCE, А Р. & PHILLIPS, B.F. 1988. ENSO events, the Leeuwin Current, and larval recruitment of the western rack Jobster, Journal du Conseil (Interna- tional pour L'Exploration de la Mer) 45:13-21.

PEARCE, А.Е. 1991, Eastern boundary currents of the southern hemisphere. Journal of the Royal Society of Western Australia 74: 35-45.

REID, J.L. & MANTYLA, A.W. 1976, The effect of the geostrophic flaw upon coastal sea elevations in the northern. North Pacific Ocean, Journal of Geophysical Research 81:3 100-3) 10.

ROSE, К.А. CAMPBELL, С.К, & SANDERS, 5,6, 1988. Larval development of the saucer scallop Amusium balloti (Bernardi) (Mollusca: Pec- tinidac), Australian Journal of Marine and Fresh- water Research 39: 153—160.

THOUZEAU, G. & LEHAY, D. 1988. Variabilité spatio-temporelle de la distribution, de là crois- sance et de 1а survie des juvéniles de Pecren mavinuis (L.) issus des poates 1985, en baie de Saint-Brieuc. Oceanologica Acta 11; 267-283,

HATCHERY PRODUCTION OF WESTERN AUSTRALIAN SCALLOPS DEREK A. CROPP

Cropp, D.A. 1994 08 10. Hatchery production of Western Australian seallops. Memoirs of the Queensland Museum 36(2): 269-275. Brisbane. ISSN 0079-8835.

Adult scallops (Amusium balloti, Chlamys australis and Chlamys scabricostata) from Shark Bay, Western Australia were transported to 6,0001 and 12,0001 pools of raw seawater al a commercial hatchery. Adults were fed daily with cultured microalgae to improve gonad condition, Successful, induced spawnings were conducted for all species with A. balloti spawnings conducted in all months from April to December inclusive, over a 3 year period. Adults were induced to spawn by the addition of sperm and a water temperature increase. For the most successful batches, larvae were respectively reared to settlement in 12, 12 and 17 days al 22,.2+0,94°C, 24.35 * 1,2°C and 20,2 +0.8° C. Up to 6.1 million pediveligers were placed into settling tanks from one spawning, Batches of settled spat regularly exceeded 0.5 million with the highest count attained of approximately 2.4 million spat at the completion of the metamorphosis/settlement stage, Large scale hatchery production techniques were developed and a potential for aquaculture has been shown, particularly for C. australis.

Derek A, Cropp, Aquatech Australia Pty Lid, 15 Wignall Street, North Hobart, Tasmania

7000; 9 March 1994.

Ten species of scallops have been documented in W.A. waters (Wells & Bryce,1985) but an accurate number or species is difficult to obtain duc (0 species overlap and name changes.

Of commercially important W.A. species, on] Amusium pleuronectes australiae {Наће,1964) was omitted from Wells & Bryce’ s list; it was also omitted from a record of scallops in Shark Bay (Slack-Smith, 1990). Jt is occasionally part of the by-catch of the Amusium balloti (Bernardi, 1861) fishery and forms the basis of a small fishery in the Northern Territory (Young & Martin, 1989). Other commercial species are Pecten modestus (Reeve, 1852), Chlamys australis (Sowerby, 1842), Chlamys (Mimachlamys) asperrimus (Lamarck,1819), Annachlamys leopardus (Reeve, 1853) and Amusium balleri. Pecten fumatus Reeve.1852 may occur along the southern coast of W. A. (Joll, 1988) but hatchery production of it is documented (Cropp,1988a; Cropp & Frankish, 1988; Dix & Sjardin,1975). A. balloti and A, pleuronectes australiae belong to the Amusiidae; other species mentioned above bclong to the Pectinidae.

Of recent studies on hatchery production of Australian scallops (Connolly,1990; Cropp, 19882, Cropp & Frankish, 1988; Dix & Sjardin, 1975; Rose ct al.,1988; Rose & Dix,1984) only one (Rose & Dix,1984) dealt with Chlamys as its commercial importance in Australia has been minimal; two (Connolly, 1990; Rose et al., 1988) reviewed hatchery culture trials on A. ballori.

Rose & Dix (1984) provided information on larvae of the doughboy scallop, Chlamys asper-

rimus, Which is similar to C. australis from W.A. They occupy similar ecological niches but the temperature regimes of their environs are 9-20°C for C. asperrimus and 17-25°C for C. australis (Cropp, 1993h)

A. balloti, the saucer or swimming scallop, is the target species for significant trawl fisheries in central Queensland (Williams & Dredge.1981) and Shark Bay, W.A, (Jo1], 1987). It is a tropical- subtropical species which appears to prefer 19- 24°C water on medium to coarse sandy mud bottoms. Its natural spat settlement and recruit- ment have been studied (McDuff, 1975; Kettle, 1984; Dredge,1981; Campbell, 1987; Sumpton et al.,1990) as has hatchery culturing (Rose et al., 1988; Connolly,1990), These studies were hindered by the tendency of the metamorphosing larvae not to exude a strong byssal thread (Rose ct al.,1988; Dredge,1981). The attachment was also found to be for a short time period only (Rose et a1.,1988), unlike Pecten or Chlamys (Dix & Sjardin,1975; Rose & Dix,1984; Sause et al., 1987; Hortle & Cropp, 1987; Cropp,19933), Im- provements in broodstock conditioning and lar- val rearing techniques (Gwyther et аї.,1991; Cropp.1988a) have been implemented and fur- ther developed in the study reviewed herein.

In Shark Bay the scallop by-catch of the A. ballati fishery is c.1-5% C. australis, C. scabricostata and A. leopardus (plus occassional rarer specics). This by-catch is generally returned lo the sea as processing is deemed difficult and markets have not been established. However, the meat and gonw! from processed C. australis 18

270

almost identical to that from the cooler water C. asperrimus, which is common in Tasmania and well reccived on the market. Hence a potential exists for marketing C. australis, Chlamys scabricostata does not grow to the same adult size that C. australis or C. asperrimus does (S. Slack- Smith pers. comm.). C. australis was deemed as having a better potential for aquaculture,

The most common spat production technique for overseas scallop culture is based around col- lection of natural spat at sea (Ito,1988; Bull, 1988). From this perspective alone, it is necessary to be able to distinguish between larvae which are likely to be present in the water column al similar times, For this reason а small scale hatchery trial involving C. scabricostata was conducted prior to the culture of C. australis. Adults of this species were induced to spawn and the larvae reared under the same conditions as for C. australis. Larvae produced by A. ballot adults have been reared under similar conditions and are distinguishable from C. australis and C. scabricostala.

Various Chlamys species are cultured in hatcheries and in some areas grown-out in culture operations overseas (Broom & Mason,1978; Mason, 1983; Cropp,1988h). Chlamys generally attach firmly to substrates upon settlement and remain attached for several months. Interception of the natural settlement and spat attachment process (with artificial substrates) has been found to be viable (Hortle & Cropp.1987) and economi- cally feasible on a large scale (Rhodes & Wid- man,1980; Маги,1985; Сгорр,1987) for namer- ous different species overseas and within Australia (Bull,1988; Cropp,1988b). It has al- lowed industries to develop through the availability of large amounts of spat.

Amusium, however, exhibits a weak and tem- porary attachment (byssus) only (Dredge, 1981; Gwyther et al.,1991) and collection of significant quantities of spat at sca is therefore unlikely. This necessitates the hatchery production of spat, The small population of C, australis in Shark Bav, suggests that natural spatfall would probahly he minimal and thus, if an aquaculture industry was to develop for this species, hatchery culture would also be necessary, Significant quantities of C. scabricostata would probably be obtainable from spat collectors deployed in Shark Bay, hence the hatchery trial simply examined larval development in this species.

An assessment of meat recovery (as % of live weight) from various species suggested thal most market potential was in A. ballot! and C.

MEMOIRS OF THE QUEENSLAND MUSEUM

australis. Larval development of these species was carefully examined in addition to a brief larval rearing trial with C. xcabricostata. The southern species, P. modestus is acknowledged to have aquaculture potential also. The fact that it is similar to P. fumatus, which has been produced in commercial quantities in a hatchery, suggests that the larval rearing techniques for both species would probably be similar, Thus no special effort was made to rear the species іп a hatchery, As an aquaculture species, A. leopardus was perceived to be inferior due to slow growth and relatively low meat recovery from live weight; consequent- ly ho hatchery work was conducted on this species.

MATERIALS AND METHODS

Saucer scallops were collected from trawlers in Shark Bay, between April and October of each year from 1989 to 1991. Broodstock for the C. scabricostata spawning were collected in June 1990, and for the C. australis spawning in July 1991, The scallops were obtained from sorting trays, placed into either small portable tanks con- taining aerated water or into steel mesh baskets in the vessels’ circulating tanks. Scallops held in the vessels tanks were placed into small portable tanks upon arrival in port. They were transported in the tanks, hy road, to a hatchery at Camarvon and placed in 60001 and 12000] above-ground swimming pools, at c.15-20°C, for 5 days prior 10 а spawning being attempted with some of the animals. In mid-winter, 2 kW clectrical immer- sion heaters were used to maintain the water temperature.

Saltwater was pumped through cartridge filters in the series: 20pm, 10pm, Sym, 24m and lum. Broodstock pools were filled with 20m filtered water, larvae tanks with 1—204.m filtered water, depending on the daily water quality (thorough filtering for dirty water), and Im filtered water was used for algal cultures.

During the broodstock holding period, 50% of the pool volume was changed at least every second day and on occasions daily. Initially, volumes of a non-axenic algal culture, Terraselt- mis suecica, were added daily in sufficient quan- tity to establish a food cell density in the holding pool of 30000—40000 cells mi’. After early gonad conditioning work exhibited poor results. the algae species was changed to another non- axenic alga, Chaetoceros gracilis. When avail- able, this diet was supplemented (with approximately 5000 cells тї!) by non-axenic

HATCHERY PRODUCTION OF WA SCALLOPS 271

TABLE 1, Average annual results for each of the development stages per spawning batch of A. balloti.

eat но. ot Bashes Не Females! E | D. | —P | Peseta Size (uri) |“ Doves settee | ТЛ | 1326 | 27.4005 | 1.4298 | 68658 | — 20245 | isa |

i ou» uem ewe [ене ша [ци — Hen E eee ee ee чар

F= No. Fertilized eggs (x 10°); D= No. 'D' veligers (x 105; P= No. Pediveligers (Сгорр,1993а)

TABLE 2. Average annual size and growth rates of A, balloti larvae per batch. Only batches where an accurate Day 2 and pediveliger size were available are documented in this table, hence the batch and pediveliger

difference to Table 1. Pediveliger size is taken as the larval size on settlement day (Cropp, 19932).

Size of Г” e day 2( TIR 119.70

Po Batches

1989| 10

Chaetoceros calcitrans, Pavlava lutheri and Tahitian Jsochrysis (aff.) galbana.

Gonad condition of live scallops was monitored visually on a regular basis. When well developed or mature gonads were apparent, selected animals were cleaned and a spawning was attempted. In most spawnings, 4—10 male and 10—20 female A. balloti were used. For the other spawnings, 3 male and 6 female C. australis, and 2 male with 4 female C. scabricostata were used. A combina- tion of water temperature increases and the addi- tion of sperm extracted from spare broodstock were used as spawning stimuli.

RESULTS

Thirtyfive successful spawnings of A. balloti were conducted over the 3 years (Cropp, 1993a)(Tables 1,2). A maximum of about 6 mil- lion and often in excess of 3 million eggs were obtained from A. balloti females, up to 4.5 million eggs from C. australis females and about 0.5 million eggs per C. scabricostata female resulted from induced spawnings (Сгорр, 19936).

Larvae were reared in larvae tanks at a salinity of 35ppt and an average temperature of 22.2+ 0.94*C (mean s.d.) for А. balloti, 24.35+1,2°C for C. australis and 20.2--0.8"C for C. scabricos- tata. The algal diet was composed of similar portions of C. calcitrans, P. lutheri and Tahitian Г. (aff.) galbana at a density increasing from 10000 cells тЇ`! on day 2 up to 15000 cells mr’ at day 12 (settlement) and then to 25000 cells ml"!

Pediveliger size (jum) Daily growth of larvae, dav pem 2 to settlement RENE A m day”

214.38 14.30 123.30

| | 20738 | 78 | 1540 |

746 |

for settled spat. The diet of one batch of A. ballot larvae reared in July-August 1991 (Fig.1) is rep- resentative of that fed to other larval batches. Larval water was changed totally on or about every two days. For the most successful batches, larvae were respectively reared to settlement in 12, 12 and 17 days (Cropp,1993a,b).

Larval development for A. balloti commenced with eggs of 75.9+4.4pm (n=40), a first ‘D’ stage veliger (day 2) of 123.3+2.06.m and a pediveliger of 211.0 1.41,um (Fig.2). Larval development of A. balloti as documented (Rose et 31,1988) was verified in this work. For the batch being examined, 4.1 million pediveligers were put into settlement tanks with 30 mesh spat

BE Cealcitrans Ш Puthen Bl sachrysis

Celle/ larvae

FIG. 1. Algal diet for A. balloti larvae during the culture phase, July-August 199].

272

700. S ою = 2 500. © " $ «o 9 i 300. z ў

100, Larvar

FIG, 2. Growth of A. ballori larvae and spat, July- August 1991 (Cropp,1993a).

collectors. On day 19 spat were 362 jum in size, and by day 28, 1.4 million spat of 772 jum in size were present (41,333+4,509 spavcollector plus 160,000 loose spat). The shell of spat gradually changed from opaque to white as they grew (74mm), a feature which has not been docu- mented previously. It is also an aspect to be considered when identifying naturally occurring spat collected in tropical and sub-tropical areas.

Mature eggs of C. australis were 62,2+2.2pm (n =30) and the first D-shaped larvae were 108.5+4.1 um long (Fig.4). Total eggs produced from the 4 females was 12.55 million (Fig.5). By day 4 the larvae measured 124.1 *-5.0j.m long. The D- shaped larvae developed rapidly up to day 8 when a characteristic scallop larval shape was displayed.

E

Egis

b 8

Number of Eggs, Larvar, Spat [x 108] B

Eetllement

FIG. 3. Number of A. balloti eggs, larvae and spat surviving during the culture phase, July-August 1991 (Cropp,19933).

MEMOIRS OF THE QUEENSLAND MUSEUM

Precise size of fully developed pediveligers is difficult to ascertain; for C. australis, a sample of swimming pediveligers taken on day 12 had a mean length of 203.6+12.1рт, At that stage c.50% of the larvae had an motile foot. A sample of settled spat on day 15 had a length of 296.9+48.3 jum. Thin new (dissoconch) shell was evident on the outer edge of spat. About 2,4 million spat (39.3%) settled from 6.1 million eyed larvae at day 12. The spat count included an estimation of those spat attached to the wall and bottom of the tank. A sample of 5 collectors was washed and spat counted on day 16, The mean count per collector was 37,8002-6,058; spat were approximately 300j.m.

Eggs produced by C. scabricostata females had a diameter of 60—63,.m (Fig.6). Sufficient sperm

Mean shell Jeagth (pm) Settlement

Day

FIG, 4. Growth of C. australis larvae and spat: (shell length with s.d.); (n = 30) (Cropp,1993b).

solution was added to give a ratio of 4—5 sperm per egg (with a total of 1.54 million eggs, Fig.7). After 46 hours (day 2) at 21.8°C, 800,000 larvae (51.95% of eggs) had developed into D-shaped veligers with a mean length of 103.4рт (Figs 6,7) and 82.2jm height. At day 13 the larvae were 197pm long and exhibited a prominent eye-spot. By day 17 numerous pediveligers were evident. The 75,000 remaining larvae were 220um long and had grown at a rate of &.33рт day ! since becoming D-shaped larvae at day 2. Metamorphosis and settlement. occurred over days 17-20. By day 21 settled spat were 250m long and exhibited new shell.

DISCUSSION

Examination of the commonly assessed phases

HATCHERY PRODUCTION OF WA SCALLOPS

Number of Eggs and Larvae (106)

Settlement

Day

FIG. 5. Number of C. australis eggs and larvae surviv- ing during the culture phase (Cropp.1993b).

of the larval rearing stage for А. ballorí indicated that culture in 1991 was markedly more success- ful than culture of larvae in 1990 and especially 1989. A combination of factors was responsible for this success. The major improvements were in broodstock conditioning, and thus quality of eggs, the effectiveness of the water filtration sys- tem (improved water quality) and variations in the larval culture conditions (Cropp. 19932).

Use of high quality mature eggs produced benefits throughout the larval culture period. Less mortality occurred and larger veligers resulted. Subsequent use of water with a stable tempera- ture and salinity further enhanced the growth and survival of larvae.

An average survival figure in 1991 of 14,8% from eggs to D-shaped larvae and 64.4% from

È

B

ы

Mean shell length (yn) З

Seulement

FIG. 6. Growth of С, scabricostata larvae and spat: (shell length).

D-shaped larvae to pediveligers compares favourably with data from Canadian research (Thompson et al.,1985) on the Japanese scallop Patinopecten yessoensis. Larval rearing of this species produced survival rates for corresponding phases of 1096 and 1096. These figures may have resulted from the use of antibiotics and non- axenic algae in the culture process.

Rose et al. (1988) recorded a growth of 5.21.m day"! for A. balloti larvae from the first D stage to the umbonal veliger, then 6.3m day” until the pediveliger stage. Larvae in our study attained àn overall average (for 1991) of 7.5j.m day” for the period from the first D-shaped larvae (day 2) to pediveliger. The batch spawned on 24 July 1991 gave an overall growth rate of 8.7m day" for the same phase.

Rose & Dix (1984) found that the mean egg

Spel

Number of Eggs, Laryae, Spat x 106}

Settlement

FIG, 7. Number of eggs, larvae and spat for C. scabricostata during the culture phase.

diameter for C. asperrimus was 61.5 +0.4рт, the first D-shaped larval stage with a prodissoconch I shell occurred after 2 days and was 108 рт long, and that fully developed pediveligers occurred on day 19, when larvae were 194рт long. Cor- responding data for C. australis were 62.2+ 2.2 jum, 108.5+4.1 jum and 203.6 12.1 рт (day 12) respectively.

C. australis larvae were reared at 23-24°C іп a subtropical area, whilst C. asperrimus larvae (Rose & Dix,1984) were reared at 17-18?C in a cool temperate area. The higher rearing tempera- ture for C. australis is thought to be responsible for the comparatively short larval period.

Larval development appears to be very similar for C. asperrimus and. C. australis and the spat settle at a similar size. In the C. australis trial, 63.756 of eggs developed into D-shaped larvae,

274

76.3% developed from D-shaped larvae to metamorphosis and overall, 43.6% of eggs developed through to metamorphosis. These are extremely high survival rates and as far as known, they exceed those documented for hatchery cul- ture of any other species of scallop world-wide.

Overall, these trials have established viable techniques for the production of commercial quantities of А. balloti and C. australis. For A. balloti this may mean that large quantities of spat could be used to enhance the wild fishery, al- though this is unlikely to be required at present due to the buoyant state of the fishery, Catches recorded recently in W.A. have been higher than previous peaks in the history of the fishery. As- socialed declines in market value, and a depressed world scallop market, have threalened the commercial viability of the scallop trawling industry and eliminated the possibility of a viable culture industry at present. For C. australis, hatchery produced spat may allow its aquaculture potential to be developed as it has been for C. asperrimus in Tasmania. However, the economic value of C. australis would be affected by the depressed market and commercial viability of a culture operation would need careful examina- tion before proceeding.

ACKNOWLEDGEMENT

This research was funded by the Fishing In- dustry Research and Development Council.

LITERATURE CITED

BROOM, MJ, & MASON, 1. 1978, Growth and spawn- ing in the Pectinid Сату opercularis in relation to jure and phytoplankton concentration. Marine Biology 47: 277-285.

BULL, M.F. 1988. A New Zealand scallop enhance-

ment project-cost and benefits. Рр, 154—165, In M.C.L. Dredge, W.F. Zacharin & M. Joll (eds), ‘Proceedings ofthe Australian Scallop Workshop, Hobart, Australia’. (Tasmanian Government Primer: Hobart),

CAMPBELL, С.К. 1987, ‘A final report to the Fishing Industry Research Committee on the recruitment into commercial stocks of the saucer scallop Amusium japonicum balloti,’ 27p.(Queensland Department of Primary Industries: Deception

Bay)

CONNOLLY, N.M. 1990. Some aspects of the maricul- ture of the tropical/subtropical scallop, Aemusium balloti (Bernardi). Hons Thesis, James Cook Univ. North Queensland, 93

CROPP, D.A. 1988a. 'FIRTA АЗ Hatchery produc- tion of scallop spat for large scale reseeding trials. Final Report’. (Fishing Industry Rescarch Trust

MEMOIRS OF THE QUEENSLAND MUSEUM

Account, Department of Primary Industry: Can- berra

CROPP, D.A. 1988b. Scallop culture in the Pacific

Re. Region, Pp. 193-211, In Evans, L.H. & O'-

ivan, D.B., (eds), ‘Proceedings of the First jim s Shellfish Aquaculture Conference Perth" (Curtin University of Technology; Perth).

CROPP, D.A. 1992, ‘Aquaculture of the saucer scallop Amusium balloti, Final Report’ (Fisheries Re- search and Development Corporation, Depart- ment of Primary Industries: Canberra),

CROPP, D.A, 1993a. Development of large scale hatchery production techniques for Amusium bal- юй (Bernardi, 1861) in Western Australia. Aquaculture 115: 285-296

CROPP, D.A, 1993b, Hatchery culture potential of the scallop Chlamys australis in Western Australia. Aquaculture 115:31-40

CROPP, D.A. & FRANKISH, KR. 1988. Cost coin- parion of hatchery and naturally produced spat

or the scallop Pecten fiwnatus Reeve. Pp. 196- 225, In M,C,L. Dredge, W.F. Zachann & L.M. Joll, (cds), ‘Proceedings of the Australian Scallop Workshop, Hobart’ (Tasmanian Government Printer: Hobart),

CROPP, R.A. 1987, Feasibility of scallop culture in Tasmania, Tasmanian Department of Sea Fisheries Technical Report 15: 1-24,

DIX, T.G. & SJARDIN, M.J. 1975, Larvae of the commercial scallop, Pecten meridionalis From Tasmania. Australian Journal of Marinc and Freshwater Research 26; 109-112.

DREDGE, M.C.L. 1981, Reproductive biology of the saucer scallop Amusium japonicum ballor (Ber- nardi) in central Queensland waters. Australian Journal of Marine and Freshwater Research 32: 775-787

GWYTHER, D., CROPP, D.A., JOLL, L.M. & DREDGE, M.C.L. 1991. Australia. Develop- ments in Aquaculture and Fisheries Science 21: 835-851.

HORTLE, M.E. & CROPP, D.A, 1987, Settlement of the commercial scallop. Pecten fumatus (Reeve) 1855, on artificial collectors in eastern Tasmanian waters, Aquaculture 66: 79-95,

TTO, H, 1988, Sowing culture of scallop in Japan. Pp. 63-68, In Sparks, А.К. (ed.), ‘New and innovative advances in biology/engineering with potential for use in aquaculture. (NOAA Technical Report NMFS 70),

JOLL, L.M. 1987. The Shark Bay SEM Fishery, Fisheries Management Paper 11: 1-123,

JOLL, L.M. 1988. History, biology and managernent of Westem Australian stocks of the saucer scallop Amusium ballot, Pp,30-41. In M.C.L, Dredge, W.F, Zacharin & L.M. Joll, (eds), ‘Proceedings of the Australian Scallop Workshop, Hobart, Australia’ (Tasmanian Government Printer: Hobart).

KETTLE, В.Т, 1984, Settlement and growth of the Jocal scallops Amusium pleuronectes (Linné) and

HATCHERY PRODUCTION OF WA SCALLOPS

Amusium balloti Habe. Hons, Thesis. James Cook Uni. North Queensland. 93p.

MARU, K. 1985. Ecological studies on the seed produc- tion of scallop, Patinopecten yessoensis. Journal of the Hokkaido Institute of Fisheries 27: 1-53.

MASON, J. 1983. ‘Scallop and queen fisheries in the British Isles’. (Fishing News: Farnham, Surrey).

MCDUFF, M.M. 1975. A study of some aspects of the population ecology and reproductive biology of Amusium pleuronectes (Linné) in coastal waters of Townsville. Hons. Thesis James Cook Univer- sity. 85p.

RHODES, E.W. & WIDMAN, J.C. 1980. Some aspects of the controlled production of the bay scallop (Argopecten irradians). Proceedings of the World Mariculture Society 11: 235-246.

ROSE, R.A., CAMPBELL, G.R. & SANDERS, S.G. 1988. Larval development of the saucer scallop Amusium balloti (Bernardi) (Mollusca: Pec- tinidae). Australian Journal of Marine and Fresh- water Research 39: 153-160.

ROSE, R.A. & DIX, T.G. 1984. Larval and juvenile development of the doughboy scallop, Chlamys (Chlamys) asperrimus (Lamarck) (Mollusca: Pec- tinidae). Australian Journal of Marine and Fresh- water Research 35: 315-23.

SAUSE, B.L., GWYTHER, D. & BURGESS, D. 1987. Larval settlement, juvenile growth and the poten- tial use of spatfall indices to predict recruitment of

275

the scallop Pecten alba Tate in Port Phillip Bay, Victoria, Australia. Fisheries Research 6: 81-92.

SLACK-SMITH, S.M. 1990. The bivalves of Shark Bay, Western Australia. Pp. 129-158. In P.F. Berry, S.D. Bradshaw & B.R. Wilson, (eds), ‘Re- search in Shark Bay. Report of the France- Australe Bicentenary Expedition Committee.’ (Western Australian Museum: Perth).

SUMPTON, W.D., BROWN, I.W, & DREDGE, M.C.L. 1990. Settlement of bivalve spat on artifi- cial collectors in a subtropical embayment in Queensland, Australia. Journal of Shellfish Re- search 9: 227-231.

THOMPSON, D., BOURNE, N, & MANSON, C. 1985. ‘Scallop breeding studies’. (Pacific Biologi- cal Research Station: Nanaimo, British Columbia, Internal Report) 16p.

WELLS, F. & BRYCE, C.W. 1985. ‘Seashells of Western Australia’. (Western Australian Museum: Perth) 207p.

WILLIAMS, M.J. & DREDGE, M.C.L. 1981. Growth of the saucer scallop, Amusium japonicum balloti Habe in central eastern Queensland. Australian Journal of Marine and Freshwater Research 32: 657-666.

YOUNG, P.C. & MARTIN, R.B. 1989. The scallop fisheries of Australia and their management. Aquatic Sciences 1: 615-638.

MODELLING MANAGEMENT MEASURES IN THE QUEENSLAND SCALLOP FISHERY

M.C.L, DREDGE

Dredge, M.C.L. 1994 08 10: Modelling management in the Queensland scallop fishery. Memoirs of the Queensland Museum 36(2): 277-282. Brisbane. ISSN 0079-8835,

The saucer scallop Amusium japonicum balloti is the basis of a trawl fishery with an average annual meat production of about 1,000 tonnes in Queensland. A variable size limit (90mm in summer and autumn, 95mm in winter and spring) and a ban on fishing during daylight are significant components of the management package imposed on the fishery.

Effects of alternative management regimes on yield per recruit, value per recruit and spawners per recruit have been evaluated using a modelling procedure. The effect of variation in growth parameters has been interpreted in the model.

Results indicate that increasing the size limit to 95mm throughout the year would increase spawners per recruit minimally while decreasing value per recruit 15-2096. A 95mm size limit for most of the year with 24 hour a day fishing, would decrease spawners per recruit by 15-35% in the ranges of F examined, while increasing relative value per recruit only at lower exploitation levels.

M.C.L. Dredge, Queensland Department of Primary Industries, Southern Fisheries Centre,

P.O. Box 76, Deception Bay 4508, Queensland; 15 April, 1994,

Queensland’s saucer scallop (Amusium japon- icum balloti) fishery is a component of the state's multi-species trawl fishery. Some 900 trawlers (10-20m long), are licensed to fish for a number of species of penaeid prawns. slipper lobsters (Scyllaridae), crabs and scallops. Catch and effort data were monitored voluntarily in particular fisheries, but have been compulsory and com- prehensive since 1988. The current return system calls for daily records of effort and catch within 30'x30' spatial grids, with some data being avail- able at a finer spatial resolution (6' x6").

The trawl fishery annually takes c.10,000 ton- nes of product, with variation in total production and species proportions between years. Scallops contribute an average of c. 1000 tonnes of meat annually (Neil Trainor, pers. comm.).

All of the state’s licensed trawlers are legally entitled to fish for:scallops. Not all vessels do catch them, however. During 1988-1992, 270- 360 vessels reported catches of scallops (Neil Trainor, pers, comm.), There appears to be excess fishing capacity in the state's trawl fleet in the context of taking the state's annual scallop catch.

Queensland's saucer scallop stock was first fished in the mid 1950's (Rucllo,1975), when prawn trawlers working out of Hervey Bay took appreciable quantitics. The fishery remained an irregular ‘off season' source of income for prawn trawl operators unti] the mid 1970's, when serious attempts to export saucer scallop meat to

the U.S. and south east Asia became profitable (Dredge,1985). Effort directed towards scallop stocks increased rapidly (Fig. 1), total catches in- creased then levelled off, while catch rates rrr da by an order of magnitude during 1978- 1985.

The scallop fishery has been managed through both input and output controls, largely since 1985 (Table 1). Management was initially directed towards maximising yield per recruit through the use of a size limit, initially set at S0mm shell height (SH), but later increased (Table 1). As effort directed at the scallop resource increased and catch rates fell, managers expressed concern about the state of the resource and directed management measures towards maintenance of spawning stock levels. These included introduc- tion of a variahle size limit (90mm SH in summer and autumn, 95mm in winter and spring) designed to reduce fishing effort during the species” winter spawning season, introduction of daylight trawl closures in order to reduce fishing effort, and the short-lived trialing of areas closed to fishing as spawning stock protection sites.

The industry has repeatedly expressed concern about the management package which has evolved over the past 10 years. Some fishermen regard the daylight trawl ban us discriminatory, Others would prefer to have a year-round size limit of 90 or 95mm SH. An alternative proposal involves 24 hour a day fishing while having a

278

MEMOIRS OF THE QUEENSLAND MUSEUM

1,800 Catch 1,600) Effort Ж CPUE (ka/boat/day) 1,400 1,200 R в 1,000 FN c i f а С {1 { ‚= З воо i} | à г X oet і \ ^ 22" ү an Ж-Ж | F + зй Y. j \ + га 400, + A / "n эж. * + ` 2 Y 200| / p ,"x-x*-* P Lii:

Tue Ж-Ж у

of computer based simulations. The results = of this evaluation form jV the basis of this paper.

MATERIALS AND METHODS

Theoretical yield per recruit outcomes from à range of management scenarios were model- led using QuickBasic programmes based on those described in 5 ' Dredge (1992), The programmes were struc- tured to create a series of overlaying two dimen- sional matrices.

10

boat days (thousands)

AO A^ AB 49 © ох dr qo q* L d

95mm SH size limit for May-January, and a 90mm SH limit for February-April, inclusive. These alternatives have been evaluated in terms of meat yield per recruit, value per recruit, and spawners per recruit, using outputs from a series

FIG.1. Total landings and catch rates from the nda saucer scallop fishery.

Tur MopEL

In the initial matrix, one axis defined num- bers in a series of recruitment cohorts and the other defined time. The resultant matrix developed a series of cohorts linked to recruitment events over time. All simulations were based on two identical, normal- ly distributed recruitment pulses being fed into

TABLE 1. Summary of management "aL y in the scallop fishery (P. Pond, pers. comm.)

Gear size | ттам1 closures Designated Preservation zones shucking areas

Daylight trawl ban 1/10-31/1

Daylight Dy] ban lifted

11/84 Combined | һеайгоре апа

footrope <109т 784 | — 85mm č | [5m] # BENE. EIER LN

EF FEET [| 90mm 11/90 - 4/91

Daylight trawl

each year Fue uni: Гра сне — & rawa n Ba Three 10-minute ENS

10-minute areas closed to fishing

ban

MODELLING MANAGEMENT OF QLD SCALLOP FISHERY

the model over a 16 week time period, in order to simulate a four month, bi-modal spawning process commencing in early winter (Dredge,1981). The model was stepped through the ‘time’ axis, both to feed in recruits and to diminish the numbers of scallops in each cohort through a process equivalent to natural mortality, i.e. though the process № = Ni.e™, where Ni represents numbers at time t, Ni+1 are numbers at time t+1, and M the coefficient of natural mor- tality. M was ascribed a value of 0.02 week"! (Dredge, 1985),

The second matrix was used to estimate size at age (shell height) in each cohort at each age. Growth rates of scallops are known to vary with location, apparently as a function of depth and tidal regime (Williams & Dredge,1981; Dredge & Robins-Troeger, unpubl. data). Three different growth scenarios were used in this model. Sub- sets of this matrix were used to ascribe size at age for scallops from areas where growth was rapid (Lc-1050 -g(0055*0y" intermediate (Li-100(1-e (.051*. and slow (Li-97(1-e: ©"), with t in weeks. Von Bertalanffy growth parameters were derived from Williams & Dredge (1981) and Dredge & Robins (unpubl. data). The model was based upon 55% of scallop being taken from ‘fast growth’ areas, 35% from ‘intermediate growth’ rate areas, and 10% from “slow growth’ areas. These figures are based on the average spatial distribution of catch for 1989-1991 inclusive (Trainor pers. comm.).

A third matrix was used to convert shell height to adductor weight for scallops in each cohort at each age. Monthly shell heightto adductor weight conversions, based on those in Williams & Dredge (1981), were used for this procedure. A dollar value was ascribed to scallops in each cohort at each age by multiplying numbers of survivors by meat weight by unit value of meat in a fourth matrix. This required a correction factor based on the individual meat weights, as there is an appreciable difference in scallop prices based on individual meat sizes (Hart, this memoir).

Fishing was simulated through a process which involved identifying those cohorts in which scal- lops were larger than a given (‘legal’) size and increasing the mortality rate to include a com- ponent for fishing mortality (F), ranging between light (F=0.005 week!) to very heavy (F=0.040 week"). The resultant ‘catch’ of both meat weight and value was accumulated as the model was stepped through time.

An index of the number of spawning scallops was developed by averaging the sum of the num-

279

value Spawning index

value spawn into

ees

zm жа 1000 + = 2,800 an t га "ы-н! 1. © „| INTERMEDIATE Rey) -r ù wo = 5 e 2 1500 Е > E 100) 2 тот 5 л E 2 ээ) T маше o C" узуп "i ^ > & # g S $ rd 8?

Spawning index

ыу) уче Ч

+ shaw ingen} oy

о А n а ^ > 2 2 E d o ef з Q9 у So =

Fishing mortality

FIG.2. Value per recruit and spawners per recruit from scallops with differing growth parameters.

ber of one and two year old scallops which sur- vived at the beginning and end of the winter spawning period. This index has been used as an index of spawners per recruit.

MANAGEMENT SCENARIOS

Yield per recruit in meat weight and dollar value, and spawners per recruit were estimated in the following management scenarios:

1) A 90mm SH size limit in summer and autumn and 95mm SH size limit in winter and spring, with no daylight fishing (the existing management situation),

280

250- 35d Size limit: 90 mm Nov ~ Арг, 85 mm May - Dot

300 = 200 3 За м 3 "—- 4250 o р - ж + m б = = es — 2 - gon "LIBELLI Um 5 + a a 10 t ш 120 = > = = m ¥ 100 & > a 50 in

T © value БО

E ® & 2 m D e

250 1200 Size limit: 85 men year round p =A 250 = _ Ж n aaa gs yn 3 5 B 8 wn ine `~ | — gi Ba | je 190 a a Р - mi # E I + mz [3 > - Я. 3 а © ^V value “"spaviner. spa 0

Pod ^ ®

Dou wo gg $ d SU g Ф = о?

No daylight closuré: assumg effective fishing aitort doubles

250 ую ie limit: 90 mm Fab - Apr, 95 mm May - Feb Г

ШЕ ——_!— 250 - т

Е 1 1

a

"value 5n

Value per recruit 8 + 5 Spawners per recruit

а АЦА

* p e A d

u] o e cv er er er ©”

бс & О.

Fishing mortality

FIG.3. Variation in value per recruit and spawners per recruit as a consequence of varying management regimes.

2) A year round 95mm SH size limit, with no daylight fishing.

3) A 95mm SH size limit in May—January, and a 90mm SH limit in February—April (inclusive), with an increase in fishing mortality commen- surate with 24 hour a day fishing throughout the year. This was achieved by assuming that the fishing mortality rate (F) doubled as a conse- quence of allowing 24 hour a day fishing.

Model runs were carried out over a 104 week time span, which approximates the effective max- imum life span of the species (Heald & Caputi, 1981; Dredge,1985). Yield per recruit and

MEMOIRS OF THE QUEENSLAND MUSEUM

spawners per recruit were estimated as a function of fishin g mortality (F) between 0.005-0.040 week .

RESULTS

Output from model runs is most readily inter- preted in graphic form.

EFFECT OF VARIATION ON GROWTH PARAMETERS

Spawners per recruit and catch value per recruit from equivalent recruitment processes were com- pared for populations with 3 sets of growth parameters. Variation in growth parameters had an appreciable effect in ‘per recruit’ output (Fig. 2). Value per recruit of slow growing scallops was 1/3-1/2 of that in fast growing scallops, with the differential increasing as exploitation rates increased. Conversely, spawners per recruit from slow growing scallops remained at near steady levels as the exploitation rate increased, indicat- ing how few attained legal size before they com- menced spawning. Spawner per recruit levels from fast growing scallops declined from about 90% to 60% of those seen in slow growing scal- lops as the rate of exploitation increased.

EFFECT OF VARIATION ON MANAGEMENT SCENARIOS

Variations in ‘per recruit’ output as a conse- quence of varying management scenarios are depicted in Fig. 3. If the output derived by modelling the existing management situation is used as a reference point, altering size limits from 90mm SH (summer and autumn), 95mm SH (winter and spring) (management scenario 1) to 95mm SH all year round (management scenario 2) would result in a general decrease of 20-35% value per recruit (rising with increasing F) and a commensurate increase of 5-12 % in terms of spawners per recruit. This is dependant upon the relative input of fast, intermediate and slow grow- ing scallops to the fishery.

Results from the model suggest that consequen- ces of changing the management regime from 90 mm SH (summer and autumn), 95 mm SH (winter and spring) (management scenario 1) to one in which effective fishing mortality was doubled (no daylight closure) and size limits were held at 90mm SH in Febniary to May, and 95mm SH for the remainder of the year (scenario 2), value per recruit would increase substantially ( 40 %) at low levels of exploitation, but change little at higher exploitation levels. Spawners per recruit would be reduced by about 10% at lower levels of ex-

MODELLING MANAGEMENT OF QLD SCALLOP FISHERY

ploitation, and up to 25% at the highest exploita- tion level examined,

DISCUSSION

The model demonstrates that yield per recruit and spawners per recruit will be markedly in- fluenced by growth parameters of scallops taken in the fishery. There is evidence that growth parameters of scallops may vary considerably over relatively small distances (Williams & Dredge,1981; Ansell et al..1991; Ciocco, 1991). Such variation in growth parameters can have a marked effect on optimum age or size at first capture for yield per recruit maximisation. Varia- tion in growth parameters have been recognised and incorporated into the model described in this paper. There is, however, no reason why propor- tions of landings from slow, intermediate and [ast growing areas should remain constant, and con- sequently the model's output should be treated as indicative. In years when a high proportion of landings come from areas where scallops grow quickly, vield per recruit may be maximised by having a larger size limit, and conversely, when scallop settlement occurs predominantly in ‘slow growth’ areas, yield would be increased with a smaller size limit. Given the lead-in time and information requirements for a management sys- tem using flexible size limits, implementation seems unlikely in the short term.

The output derived by modelling the fishery under alternative management scenarios indi- cated that variation in exploitation levels effected both trends and absolute values of yield per recruit.

Dredge (1992) suggested that a size limit of Ymm SH maintained throughout the year would have litile effect on value per recruit by com- parison with the existing 90mm SH (winter and spring), 95mm SH (summer and autumn) size limits. Output from the model used in this study suggested that increasing size limits to 95mm SH on à year round basis would induce a substantial loss to the fishery with a relatively minor increase in terms of spawners per recruit,

The management option involving size limits being set at 90mm SH in February to May, and 95mm SH for the remainder of the year, and increasing exploitation by allowing 24 hour a day trawling was examined, Results indicated that spawners per recruit would be reduced by 10- 25%, and valuc per recruit would be increased only at bow levels of exploitation. This scenario involved a fair degree of uncertainty, however, их

281

an arbitrary doubling of fishing mortality was used to simulate the effects of allowing 24 hour а day tràwling. Verification of such an arbitrary procedure is not possible.

Given the current limitations in our under- standing of spawning stock and subsequent recruitment levels, the model output indicates that the existing management package offers a reasonable compromise between obtaining max- imum catch value from the resource while main- taining brood stock levels.

By comparison, the Western Australian agency which manages a fishery for the same species has amanagement philosophy based on limited entry, minimising capture costs, and minimising con- flict between alternative fisheries in the main fishing ground (Shark Bay). Maintenance of a substantial breeding population is considered critical to management. This is achieved by having a summer closure, and a predominantly winter fishery, hus allowing the bulk of animals to spawn early in the (winter) spawning season. (Joll,1987,1989}, Size limits are not used in the WA fishery, as scallop shucking in the fishery takes place at sea-

Queensland fisheries managers seek to main- tain biological sustainability and long term economic viability of the (integrated east coast trawl) fishery while recognising social values in defining management actions (Glaister et al., 1993), The differences in management phil- osophy have resulted in fisheries which have markedly different seasonality, input costs and numbers of participants.

ACKNOWLEDGEMENTS

Neil Trainor provided many of the cateh and effort statistics from the Queensland commercial fisheries data base, SUNFISH. Julie Robins- Troeger prepared the graphics, and the editorial committee at Southern Fisheries Centre reviewed the manuscript, My thanks Io all of these people for their efforts.

LITERATURE CITED

ANSELL, A.D,, DAO, J.C. & MASON, J. 1991. Three scallop fisheries; Pecten maximus, Chlamys (Ae- quipecten) opercularis and C. (Chlamys) varia. ln S.E, Shumway (ed.), 'Scallops: biology, ecology and aquaculture’. (Elsevier; Amsterdam).

CIOCCO, N.F. 1991, Difference in individual growth rate among scallop (Chlaemnys tehuelcha (d'Orb]) populations from San Jose Gulf (Argentina). Fisheries Research 12; 31—42.

282

DREDGE, M.C.L. 1981. Reproductive biology of the saucer scallop Amusium japonicum balloti (Ber- nardi) in central Queensland waters. Australian Joumal of Marine and Freshwater Research 32: 775-787.

DREDGE, M.C.L. 1985. Estimates of natural mortality and yield per recruit for Amusium japonicum bal- loti Bernardi (Pectinidae) based on tag recoveries. Journal of Shellfish Research 5(2): 103-109.

DREDGE, M.C.L. 1992. Using size limits to maintain scallop stocks in Queensland. In D.A. Hancock (ed.), ‘Legal sizes and their use in fisheries management'. Australian Society for Fish Biol- ogy Workshop, Lome, 24 August 1990. Bureau of Rural Resources Proceedings No. 13. (Australian Government Publishing Service, Can- berra).

GLAISTER, J.G., POND, P.C & STOREY, J.G. 1993. ‘Framework for management for the East Coast trawl fishery’. (Queensland Fish Management Authority: Brisbane).

HART, B. this memoir. Dilemma of the boutique Queensland scallop.

HEALD, D.I. & CAPUTI, М. 1981. Some aspects of

MEMOIRS OF THE QUEENSLAND MUSEUM

growth, recruitment and reproduction in the southern saucer scallop, Amusium balloti (Bernar- di,1861) in Shark Bay, Western Australia. Fisheries Research Bulletin of Western Australia 25: 1-33.

JOLL, L.M. 1987. The Shark Bay scallop fishery. Fisheries Department, Western Australia, Fisheries management Paper 11.

JOLL, L.M. 1989, History, biology and management of Western Australian stocks of the saucer scallop Amusium balloti. In M.C.L. Dredge, W.F. Zacharin & L.M. Joll (eds), ‘Proceedings of the Australasian scallop workshop'. (Tasmanian Government Printer: Hobart).

RUELLO, N.V. 1975. An annotated bibliography of prawns and the prawning industry in Australia. In P.C. Young (ed.), ‘First Australian prawn seminar’, (Australian Government Publishing Service: Canberra).

WILLIAMS, M.J. & DREDGE, M.C.L. 1981. Growth of the saucer scallop Amusium japonicum balloti Bernardi in central eastern Queensland. Australian Journal of Marine and Freshwater Re- search 32: 657—666.

SCALLOP FISHERIES, CULTURE AND ENHANCEMENT IN THE UNITED STATES

SANDRA E. SHUMWAY AND MICHAEL CASTAGNA

Shumway, S.E. & Castagna, M. 1994 08 10: Scallop fisheries, culture and enhancement in Ше опна States. Memoirs of the Queensland Museum 36(2): 283-298. Brisbane. ISSN -R835.

Information is provided on distribution, commercial landings and landed value of: sea scallop, Placopecten magellanicus, bay scallop, Argopecten irradians, calico scallop, Ar- gopecten gibbus, om scallop Chlamys rubida, spiny scallop, Chlamys hastata and weather- vane scallop, Patinopecten caurinus, Where applicable, information is provided on fishing regulations and management plans, Aquaculture of scallop is limited to a few ventures utilizing the bay scallop, A. irradians. Enhancement programs are designed to reinstate populations of A. irradians to areas decimated by the "brown tide' Aureococcus anophagef- Jerens and regional efforts to provide some stability to local fishing efforts,

Sandra E. Shumway, Bigelow Laboratory for Ocean Sciences, Wesi Boothbay Harbor, Maine 04575, USA (present address: Natural Science Division, Southampron College LIU, Southampion, New York 11968, USA) & Michael Castagna, Virginia Institute of Marine

Science, Wachapreague, Virginia 23480, USA; 20 June 1994,

Scallops are commercially important shellfish worldwide (Table 1); US landings of all scallops were 40 million pounds of meat (18,000tonnes) valued at $US162.5 x 106 for 1991 (O'Bannon, 19913). This represented a decrease of 1.6 million

ounds (700 tonnes) (4%) but an increase of

US4.4x105 (3%) compared with 1990. Four species (sea scallop, calico scallop, bay scallop, and weathervane scallop) contribute to the major wild fisheries in the US with minor fisheries for pink scallop and spiny scallop. In 1983 and 1987 Massachusetts reported 418,800 and 29,400 pounds (190 and 13tonnes) respectively) annual landings of the Icelandic scallop, Chlamys islan- dica and Rhode Island reported landing 2,800 pounds (1.2tonnes) of this species in 1983. C. islandica is not regularly fished in US waters.

Aquaculture and enhancement efforts are limited activities in the US to the extent that scallop aquaculture is not even listed by FAO in their annual statistics reports (FAO, 1992); how- ever, where these activities do occur they con- tribute to local economies. Further, production from domestic activities (fisheries, aquaculture and enhancement) does not totally meet supply requirements and scallops are regularly imported from other countries (Tables 2,3).

We present a brief overview of US scallop fisheries, aquaculture and enhancement efforts, 1 is not intended to be comprehensive,

COMMERCIAL FISHERIES

Sea $сА ОР, PLACOPECTEN MAGELLANICUS This large, long-lived species attains shell

heights of 8.5ins (20cm) and supports an inten- sive fishery throughout its range from New- foundland to North Carolina. American cam- mercial fishing efforts centre on Georges Bank, coastal New England and mid-Atlantic states (Naidu,1990; Fig.1). The fishery is 2100 years old and P. magellanicus is the most important pectinid in the world (Naidu,1990). During 1976—1987 it accounted for 30% of mean annual global production of all scallop species combined (Table 1). In some years, P. magellanicus has contributed >0.5 of global scallop production. Enhancement of some species (particularly the Japanese scallop, Patinopecten yessoensis) and sporadic booms in natural production of calico scallops (A. gibbus} have relegated sea scallop landings to a seemingly secondary role. The ad- ductor muscle (meat) is the only portion com- monly marketed in the US. although there is steady interest in developing a “roe-on' product.

Sea scallops comprise the bulk of scallops landed in the US (Table 2) with New Bedford, Massachusetts being the leading producer in 1991, landing of 21.9 million pounds (10,000 tonnes) of meats (56% of national total) (O'- Bannon, 19922). The average ex-vessel price per pound of meat increased from $1053.85 ($051.75 fkg) in 1990 to 5054.04 (SUSI.84/kg) in 1991, Total catch and landed values are given (Figs 2,3; Table 4). Regional landings vary; the New England region consistently produces most scal- lops and more southerly regions the least (Fig.2).

The commercial fishery operates year-round using otter trawls and dredges. Recreational

284

MEMOIRS OF THE QUEENSLAND MUSEUM

TABLE 1. Nominal landings (MT, round weight) of scallop species. Figures in parentheses are % contribution to global production in any given year. Source: Yearbook of Fishery Statistics, FAO, Rome, Voi. 70.

| Chlamys islandica 17.068 (Iceland scallop) 1.8) (2.8)

Chlamys opercularis queen scallop)

(1.6 (LR 238,236 25.6

Patinopecten yessoensis Japanese scallo 39.4 3,649

DILLON NE | | (weathervane scallop) (0,6) (0.6) Pecten maximus 22,253 20,128 pliant scallop 2.6

3.3) Pecten jacobeus 7 (Pilgrim's scallop) =

*species fished commercially in the US.

fisheries are rare and occur predominantly in Maine where scallops are collected by divers. Management of sca scallop resources has his- torically been a local issue. US scallop manage- ment efforts started When Maine imposed a summer closure sometime between 190] and 1917, Many local management regulations are still in effect and many more have been imple- mented to conserve stocks and control gear con- flicts. No regulation of the offshore fishery existed prior to 1983 other than what the industry imposed upon itself. In inshore waters, scallop management has existed for a long time (Shum- way & Schick,1987). Maine has had long-stand- ing regulations for conservation of scallop stocks within its 3mile territorial limits; New Hampshire has had conservation regulations of a 3.251nch (8.25cm) minimum shell height and an April 15 through October 31 closed season since 1977. Massachusetts, with the largest offshore scallop fishery out of New Bedford, has had no regula- tions as it has no large inshore beds nf sea scal-

[specs — | i94 | 1985 | ios | 1087 | 1988 | 1989 | 1990 |

| (Atlantic calico scallop) 47.2) (20.8) (3.2 (11.6 (14.0) 8.0) (1.3) * Argopecten irradians 6,597 2904 І y bay scallop 0.8) (0.8) (0.9 (0.4) А

Chilean scallop) (2.8) (8.5) (3.1) (0.8 (0.9) (0.5 (0.9)

16,429 | 13,385 12,117 (3.1) ((1.8) (1.2) (L3) 14) 22) 1.9) 1.8) (6 (2.0)

(0.5) (0.4) (0.1 (0.2) (0.3) 17,353 15,357 15,812 3 (2.1) L8 (19)

ир New Zealand scallop (0.6 0.5 33 0.1 0.1 0.1 9.1

sea scallop) 12.3 17.4) (24.5) 26.2 22.3) (24.5) 124.7) | 4.0 39) | (62) | (81) 38 | пә) | (23 [World rota | 838,067 | 604215 | 530.739 | 738,606 | 868,005 | $4023 | 876636 |

7,467

2,329 2,596 (0.3 0.2 03

502,136 59.8)

571,003 65.1

lops. Each state has modified their regulations to at least comply with the US federal regulations for the Fisheries Conservation Zone (FCZ), but Maine's regulations remain even more restric- tive, with specific area restrictions or season, geartype and gear size, a ban on nighttime shing for scallops, drag size limits which vary with season and a requirement for a hand-fishing license for divers and a boat license for draggers.

Regulations in the US offshore scallop fishery, which includes Georges Bank, Gulf of Maine and mid-Atlantic Bight as far south as Cape Hatteras (Fig.1) have been imposed by industry in thc form of crew size, maximum allowable time at sea per trip, minimum time at the dock between trips and a maximum of two tows dumped on deck at one time prior to shucking. With advent of the 200 mile Fisheries Conserva- tion Zone, New England and mid-Atlantic Fisheries Management Councils developed and implemented the Sea Scallop Fisheries Manage- ment Plan (FMP) to regulate the fishery, The

US SCALLOP CULTURE AND ENHANCEMENT 28

cn

TABLE 2. U.S. supply of scallop meats 1972—89) (meat weight in million pounds) (after Dore, 1991)

mI S. commercial IUE gs Total Imports "Total Percent | Calico | =a Supply Imports

basis for managing the Georges Bank, Gulf of Maine and mid-Atlantic scallop fisheries under the FMP has been to increase yield per recruit by controlling age/size of recruitment by imposing a maximum average meat count. The FMP was implemented in May,1983, and imposed a 30 meat count per pound maximum with an equivalent shell height of 3.51nches (8.9cm). The

TABLE 3. Domestic and imported scallop species on the U.S. market

DOMESTIC

Placopecten magellanicus Calico scallop Argopecten gibbus | Bay scallop Argopecten irradians

[Bay scallop — |

[Weathervane scallop |Parinopecten caurinus |

[Spiny scallop (Chlamys hastata | IMPORTED

[Bay scallop [Argopecten irradians |

[Peruvian scallop [Argopecten purpurams |

Sea scallop

——— —

Regional Director of National Marine Fisheries Service (NMFS) immediately increased the count to 35/pound with a shell height minimum of 3.275inches (8.6cm) due to the unwillingness of Canada to go along with a 30 count maximum. This temporary change in the limits was to be in effect until January, 1984, when the limits would go to 30 meats per pound and 3.5inch (8.9cm) shell height. The 30 count regulation was delayed until January 1986 due to industry and political pressures and the 35 meat count was retained. Under this scheme of an average meat count, small scallop meats may be mixed with large meats as long as the average meets the maximum count requirement.

In 1984, a large set of scallops in the Great South Channel of Georges Bank promised to sustain the scallop fishery for some time; how- ever, most of this set was harvested at a small size and the meats were mixed with larger meats to achieve the 35 count maximum. Almost the entire set was harvested at well below its potential yield per recruit and before it was able to significantly contribute to reproduction. To prevent this from happening again, the Councils proposed Amend- ment | to the FMP that would institute a 40 count minimum meat size, which would create an

286

75° Ww 70° 65

o

MEMOIRS OF THE QUEENSLAND MUSEUM

ES

27 S, т kd

А | g NEWFOUNDLAND

50°N

GULF OF ST LAWRENCE

40*

DISTRIBUTION, COMMERCIAL QUANTITIES OCCUR OCCASIONALLY

COMMERCIAL FISHING, FREQUENTLY PERSISTENT

o

60

o

55

FIG.1. Distribution of the sea scallop, Placopecten magellanicus, and commercial fishing grounds.

average meat count of around 30, but would prohibit the mixing of scallops much smaller than the minimum size. This effort brought much criticism from the industry.

Amendment 1 to the FMP went into effect on January 1,1986, but was delayed by the Regional Director of NMFS and was rescinded May 28,1986. Scallop management then returned to the FMP and the 30 count average with a 10% tolerance (effectively a 33 count average) and 3.5inch (8.9cm) shell height was imposed. The shell height of 3.5inches is based on an average shell height to meat weight regression showing the shell height for a 30 count scallop meat.

Industry criticism has been levied against the 3.5inch (8.9cm) shell size as well. The industry arguments centred on the fact that the shell height to meat weight relationship is highly variable from location to location and from season to season (Fig.12; Ѕегсһик,1983; Serchuk & Rak, 1983; Schick et al.,1988). With scallop sets occur- ring at different locations in different years, or even in the same year, having one shell height to meat weight regression represent the whole fishery they claim is unreasonable. Currently shellstockers can harvest scallops in the mid-At- lantic Bight at 3.5inch (8.9cm) shell height that have meats too small for the at-sea shuckers to

US SCALLOP CULTURE AND ENHANCEMENT

40

30

=”

2° m

20

->

| | | " | | |

—.

TOTAL LANDINGS ( POUNDS x 108 )

IT

' ' T 50 54 58 62 66 70 74 78 82 86 90 94 YEAR

FIG.2. Landings of sea scallop, Placopecten magel- lanicus. Data from O'Bannon 1992b)

harvest even at 33 count. With the large recruit- ment of recent year classes producing a bonanza for the shellstockers and little for the at-sea shuckers, there is much asperity in the industry with cries of unfair management practices.

In response to industry criticism, the Councils put forth Amendment 2, which contains options for management of the scallop resource. During several hearings industry spokesmen made it clear that most options were untenable, or at least unpalatable to them. Current regulations require à 30 average meat count per pound standard for shucked scallops and a3.5inch (8.9cm) minimum shell height standard for unshucked scallops. ‘Fishing effort on Georges Bank is at record levels and far beyond what the resource can sus- tain in the long run’ (Anonymous, 1992).

Discussions are now focussed on implementa- tion of Amendment #4 (designed to replace the meat count system) which includes the following common elements (Commercial Fisheries News, Dec. 1992): a moratorium restricting entry into the fishery; maximum crew size of nine, includ- ing the captain; 3.25inch (8.3cm) ring size mini- mum that would increase to 3.5inches (8.9cm) the third year of the plan; 5.5inch (14,0cm) minimum mesh size for trawl gear; 30 foot (9.2m) limit on

160

Sea Scallop

120

eo e

TOTAL VALUE ($ US x 10°)

50 54 58 62 66 70 74 78 82 86 90 94 YEAR

FIG.3. Landed value of sea scallops, Placopecten magellanicus (meats). Data from O'Bannon 1992b)

the total width of all dredges and a 144 foot (44m) limit on the sweep of trawl gear; no onboard shucking and sorting machines on boats that land shucked scallops; continuation of the 12h landing windows and no at-sea transfer of scallops; con- tinuation of the 3.5inch (8.9cm) minimum shell height standard for shellstockers (fishermen who land scallops in their shells); no chafing gear, cookies orother devices which obstruct the top or sides of the scallop dredge and a 5.5inch (14.0cm) minimum twine top on top of all dredge gear; annual permits and mandatory data reporting for vessel owners, dealers, brokers and processors as weli as licenses for vessel captains; continuation of the meat count as an alternative to the follow- ing gear restrictions: increased ring size, 5.5inch (14.0cm) trawl mesh, 5.5inch (14.0cm) twine top, and prohibitions on chaffing gear, cookies and other obstructing devices. In additions, there arc four alternatives proposed: 1) (preferred) limited days at sea by vessel group (full-time fleet, part- time fleet, occasional fleet); 2) limits on days at sea; 3) adjustable trip limit with fixed layover; 4) fixed trip limit with adjustable layover. Inasmuch as the goals of management are to optimize yield while at the same time stabilizing

288 MEMOIRS OF THE QUEENSLAND MUSEUM

TABLE 4. Historical catch statistics (total catch by regions) for sea scallops, (Placopecten magellanicus), for the period 1950—1991 (numbers in thousands). (O° Bannon,!992b)

| Year | NewEngland | Middle Atlantic | ^ Chesapeake | “South Atlantic | _ To | Rounds | Dci | Pomas [Dele | Tode | Dol. | Pounds | Dotty | Tess | реа | | 1950 | 13753 | 6384 | 6135 | 2781 | 92 | 39 | — | — | 19980 | 9204 | osi | маз | ееп | aoso | з | єз | ж | с алав вза | 1952 | 15392 | 9093 | 3205 | 1721 | 32 | m | — | — | 18629 | 10,832 | Les p sse aee [ase [ims | «4 БИП | — оза | золе | | 1954 | 15.594 | 7.028 | 207 | 9: | — | — | — | — | wes 7976 | | 1955 | 16848 | 8821 | 5244 | 2610 | 33 | wm | 2 | 2 | 22125 | 1449 | | 1956 | 16,881 | 9109 | 3164 | 1700 | 21. | з | — | — | 200% | 10,822 | 1957 | 18,781] 9119 | 2167 | 1040 | в | 21 | — | — | 20994 | 10.80 | | 1509 | 16410 | 7941 | 2324 | 1097 | 243 | 102 | — | — | 18977 | 9140 | | 1959 | 20259 | 9.05 | 3949 | rgia | 436 | в | — | — | 24,684 | 11,805 | [ 1960 | 22462 | 7,823 | 3356 | 1153 | 781 | 290 | — | — | 26599] 9266 | | 196i | 23.775 | 9,035 | 3.368 | 1.238 | sis | п | — | — | 2746) | 10404 | Lm» | зын | sasz | 288 | LM | os | M | авы | ioon [195 | rom | 8257 | 2099 | sm | 4e | | — | — | 19939 WEE я: ииз ENT NNNM MORE иии с 9 —— аана. ыз | ам ыш уыш onm ы | в | m, Due [1965 | uir | 5.520 | 2528 | 1186 | 2300 | | — | — | 15975 | 265 | RC DES GET ДЕТТИ ЕТТИН AENEA и | 1968 | 7938 | 8850 | 1,978 | 2194 | 2112 | 2268 | 42 | 42 | 12070 | 13354 | A з= P — es Lm | aser | ems] es | us | w | ws | — | — [3з | ras] [1971 | 4346 | sais | sa | m [| sas | sor | — | | 5406 | 7991 | | 1972 | 4422 | 8628 | ass | 933 | 960 | 1856 | — | — | 5850 | 11.417 | | 1973 | 3949 | 7072 | seo | 1067 | m | 3347 | — | | 5291 | 9486 | | 1974 | ави | 7174 | s34 | во | #72 | 127% | — | — | 6017 | 9267 | | 1975 | 7,081 | 1382 | 981 | 1780 | 1270 | 2330 | 421 | 421 | 9753 | 17,913 | 3627 | 5529 | 67 | 954 | 25831 | 41,951_| | 1979 | 16202 | 55,037 | 5772 | 18,717 | 7676 | 24376 | 1,694 | 4989 | 31,344 | 103,028 | | 1980 | 17.018 | 65.571 | 4.143 | 16274 | 6140 | 23.776 | sei | 2,979 | 23.162 | 108,600 | | 1981 | 19.910 | 30212 | 2,570 | 10709 | 3,350 | 14467 | 125 | am | 25,055 | 105,866 | | 1982 | 15,822 | 58,995 | 1,920 | 7244 | 2.194 | 8370 | 2 | 1 | 19,936 | 74,590 | | 1983 | 13,574 | 76385 | 2.719 | 15436 | 2515 | 16206 | 26 | 151 | 19.234 | 108,268 | | 1984 | i124 | 62652 | 2,573 | 13803 | 394 | 17747 | 170 | вв | 17,191 | 95,08 | 50,078 | 1,849 13380 | 1986 | 11,707 | 61669 | 2317 | 10388 | 4264 3,558 men 30301 | 128495 | KCNETTNETSNTONET HE: заа ие. 4.036 | 39.275 | 151.67 [ 9 | 25081 | 101932 | asas | mie | вазї | 32.807 | вз | 2324 | 38362 | 155272 |

u

ia

US SCALLOP CULTURE AND ENHANCEMENT

KS Argopecten irradians ў amplicostatus

289

Placopecten magellanicus []

Argopecten irradians irradians

; ; NI Argopecten irradians concentricus

3 Argopecten gibbus

FIG,4. Distribution of bay scallops, Argopecten irradians.

the catches, it seems reasonable that considerable attention should be paid to the high level of variability that can occur in meat weight within a given fishing area. Since a single meat count is not going to be valid ‘across the board’, different meat count and/or sheli height regulations are needed for separate fishing zones. It is further suggested that, since seasonal and yearly varia- tion in meat weights have been demonstrated, meat count regulations should be based on yearly sampling and set on a seasonal and area-specific basis. While a constantly changing count/size limit will cause problems with regard to com- pliance and enforcement, it will strip away in-

equities between harvesting techniques and in- crease yield to the fishermen by effectively in- creasing yield-per-recruit and allowing management closer to the limits of the resource.

Atatime when the scallop fishery is increasing, and for a species which experiences such drastic fluctuations, management cannot be too careful in the regulations it imposes.

Bay SCALLOP, ARGOPECTEN IRRADIANS

The species range is discontinuous along the Atlantic coast of North America between Nova Scotia and Colombia. A. irradians irradians oc- curs from Cape Cod to New Jersey where it is

790 3.5 Bay Scallop 3.0 1 і 254 Íl ae К 4 А | 8 20 i3 [ "n с Ji $ g 157 FN 5 Е: ‘il i z "gd a E 5 i ‘9 y. | gw! NT .I 5 on " » 4 0.5 i „i

A + \ 4 Pape ANY ед a ix м, А, Ner

50 54 58 62 66 70 74 78 Be BG 90 94 YEAR

0

FIG.5. Landings of bay scallops, Argopecten ir- radians. Data from O' Bannon 1992b).

replaced by A. irradians concentricus which ex- tends from New Jersey to Florida. A. irradians amplicostatus is found in the western Gulf of Mexico to Colombia (Fig.4). While this species represents only a minor component of US com- mercial fisheries (Tables 1,2), it is extremely important to local economies.

Rhodes (1990) reviewed the biology and fishery of A. irradians which is a small, short- lived species, usually spawning only once; how- ever, a second spawning by some individuals takes place in some regions. They occur in shal- low water («10m) in protected bays and estuaries, reaching a size of c,4inches (10cm) in 16 months. Meat counts are 50-100/pound (23—45/kg).

Landings vary between seasons (Table 5) and populations are dependent upon natural recruit- ment for continuation, although some enhance- ment efforts have been attempted. In 1985, bay scallop populations in the northeast were decimated by blooms of a previously unknown microalga, Aureococcus anophagefferens (brown tide’) (Tettelbach & Wenczel,1993; Fig.11). Three successive years of algal blooms resulted in virtually all native stock in the Peconic Bays and the New York fishery being eliminated, Eelgrass beds were also depleted, reducing the

MEMOIRS OF THE QUEENSLAND MUSEUM

TOTAL VALUE (5 US x 10°)

0 Sim - - - ў A: ^. 50 54 58 62 66 70 74 78 82 86 90 84 YEAR

FIG.6, Landed value of bay scallops, Argopecten irradians, Data from O'Bannon 1992b)

total area of suitable habitat for scallop settle- ment. Landings for 1991 were 438,000pounds of meats (200tonnes) valued at $US2.7 million. This isa decrease of 101,000 pounds (46tonnes) (19%) and $US436,000 (14%) compared with 1990 (O'- Bannon,1992a). Massachusetts was the leading state with 375,000 pounds (170tonnes) of meats, 86% of the national total. The average ex-vessel price was $US6.09/pound ($US2.77/kg) of meats compared with $US5.76 ($US2.62/kg) in 1990 (Figs 5,6: Table 5).

Commercial fishing records for A. irradians date back to 1858 (Ingersoll, 1886) and the intro- duction of the dredge іп 1874. Commercial fishing for A. irradians is strictly limited and there is a large recreational fishery. Harvest is usually limited to September-December. In most areas, the bay scallop fishery is a protected resource. Scallops are usually collected by diver, hand- picking or rake. Some fishermen use small boats equipped with outboard engines and one or two small dredges. Scallops are culled on board and only the meats are harvested. Catch limits are determined on a season-by-season basis hy fisheries officials in accordance with population fluctuations (Rhodes, 1990).

US SCALLOP CULTURE AND ENHANCEMENT 291

TABLE 5. Historical catch statistics (total catch by regions) for bay scallops (Argopecten sp.) for the period 1950-1991 (numbers in thousands). (O'Bannon,1992b)

|| Pounds | Dollars | Pounds | Dollars | Pounds | Dollars, | Pounds | Dollars | Pounds | Dollars | NM e | 1951 | 1253 | 959 | 101 [| 123 | 183 | % | 252 | 161 | 1789 | 1337 | | 1952 | iiss | 913 | 182 | 255 | 254 | 126 | 20 | as | 1834 | 1342 | | 1953 | 2397 | 1222 | 162 | 102 | вз | 33 | 29 | s3 | 2853 | 1410 | | 1954 | 987 | бз | 127 | no | s [| в | a | 10 | 120 | 83 | | mss | 1070 | s37 | 2% | no | w | 39 | 2з | 53 | 1,97 | 1139 | [ mss | з | am | aos | 4% | vs | 6s | m | w | 1300 | 9o | Съз [ыз [зш | вы [жт [| | ar | as CONSE |а | Cum [ims] we | sm | n: [19 | x | 4 | m [om [з | Ls | si | mo | os | ж | ps | у | 8 | э | ы ые | 1960 | 1065 | 759 | мз | вм | ө | 27 | se | 14 | 2031 | 1474 |

| w | en | se | вл | me | a | 36 | за | 198 | 1348 | | 1962 | 1425 | ові | 1353 | ssi | 18 | c: | эз | 68 | 3159 | 2067 | | mes | зәт | 492 | sm | ам | зи | 122 | 28 | s | nsu | 107 | —9 | в | sos | iw: | se | wo | TG | в | ы foar | neee | 1955 | aso | sez | om | 766 | 379 | 1% | so | за [| nes | 158 | 2s | mo | ume | e: | в | we | m |. 9 | + | мш | en | [1m | 4s | sm | ms | ow | a | zu | 7 | s | 1,007 | 1053 N CHE NE NE UM | zs | 34 | e | 4m | 1з | 122 | 1491 | 1694 | зв [um [im ш | m | ex | ss | m | e Гам оез | om |o f aos | зе | шю | о | э | юш ж | мю мт [ 197: | 2063 | 3531 | 144 | 24 | co | 42 | зв | 39 | 2315 | 386] | 1972 | i776 | 3407 | 9» | zi | i | no | 35s | м | 2032 | 3,772 | [195 | æa | 14e | zo | 467 | x | s | s | e | 104 | 2005 | [ 194 | sez | һом | c | sm | 20 | 199 | в | w | 1497 | 2103 | iere age РЕТ аа ЭИУ Toc ie aa 1926 | we [im e | me | om | 1 | a | a | 25 | 39 | [ 197 | пола | 3.085 | 199 | ago | 257 | so | в | s | ns | am | | 1978 | 152) | 4982 | 2:0 | sx | 221 | зз | 49 | o | 207 1979 | 1.382 | s967 | sas | i20 | їз | sia | 6 | зт | 1983 | тве | [1999 | 1356 | ввп | ам | аво | эв | igor | п | 29 | 2126 | 9607 | ИШЕ RE IE BA BS ин BE BEBE ии S | 1982 | 2022 | 8949 | soo | 1809 | WI шш ши ши жин Гава RET | 1983 | 1083 | &a9i | 167 | 99 | | эж | z | 75 [| m | 8067 | E IB HECUHROBT Ne HN CBE NE HET ОЕ E [ 1985 | sss | sai2 | 174 | sm | ase | 1072 | a | 10 | 1,592 [в | so | ay | 13 | в | so | вз | от | se | sss | 4786 | Lem | эш zm] 2: | э еа | в | ю | зз | эз

608 3, a8]

EE E 215 Zr

292

Gulf of Mexico

Key West

85°

MEMOIRS OF THE QUEENSLAND MUSEUM

{ Cape ^. Hatteras 7| 35° Lookout Charleston А 30° St. Augustine Atlantic Ocean Cape Canaveral 25°

80° 75°

FIG.7. Commercial fishing grounds for the calico scallop, Argopecten gibbus (after Blake & Moyer, 1990)

CALICO SCALLOP, ARGOPECTEN GIBBUS

This species supports a variable fishery off Florida (Fig.7). Locations of commercial stocks vary from year to year; however, Cape Lookout, Cape Canaveral and Cape Sand Blas are key areas. The fishery and biology were reviewed by Blake & Moyer (1990). The scallops grow to <3inches (7.5cm) and the adductor muscle (meat) is small and brownish (meat count 100—300 per pound; normally 150—200). Hand-shucking is not economically feasible; thus, even though large stocks of calico scallops were known as early as 1949, the species was not harvested commercial- ly prior to automation in the late 1970's.

During its peak (1984), landings exceeded 39 million pounds (17,700tonnes) and the fishery was almost non-existent in the late 1980's and early 1990's (Tables 1,2; Fig.8). Annual varia- tions in production impact not only the total US catch, they also determine the position of the US among world scallop producers. Landings were 286,000 pounds (122tonnes) of meats valued at $US858,000 in 1991. According to O'Bannon (19922), this represented a decrease of 849,000 pounds (390tonnes) (7576) and $US423,000 (33%) compared with 1990. All calico scallops were landed on the east coast of Florida in 1991. The average ex-vessel price was $US3.00/pound

US SCALLOP CULTURE AND ENHANCEMENT

45 Calico scallop

TOTAL LANDINGS (POUNDS X 10°) 8

76 77 78 79 ВО B1 82 ЕЗ 84 B5 ВВ 87 B8 89 90 01 EAR

FIG.8. Landings of calico scallops, Argopecten gib- bus. Data from Blake and Moyer 1990; O'Bannon 1992b).

($US1.36/kg) of meats compared to $US1,13 (SUSD.5 | /kg) in 1990,

Since stocks of A. gibbus are annual, over-fish- ing is not considered a problem, thus there are no state or federal fishery management programs. The fishery is totally dependent upon the natural population and regulation of landings is governed by a self-regulating association of industry mem- bers. Fishing efforts are limited until at least 75% of the stock at a particular location reaches a shell height of at least 38mm, the point at which much of the population will have undergone their first spawning event. A second spawning is not guaranteed and only takes place when environ- mental conditions are optimal.

WEATHERVANE SCALLOP, PATINOPECTEN CAURINUS This large, long-lived species reaching up to с.10іпсћех (25cm) and 28 years of age (Hennick, 1973) occurs from Alaska to Oregon (Fig.9). It requires 5—6 years to attain a shell height of 4inches (10cm) and reaches sexual maturity at ¢3inches (7em) shell height. Scallop meats are large, similar in appearance to those of P. magel- lanicus, and average counts are 10—40/pound (5— I8/kg). Bourne (1990) reported that minor landings of weathervane scallops occurred sporadically along the coast of Washington until the late 1950's with recorded landings for this period (1935—1952) averaging about 3601 (320tonnes) (Cheney & Mumford, 1986), A small

fishery was developed in Alaska in 1967 and landings have fluctuated widely (Fig.10; Table 5). Oregon landings for 1989-1992 were less than 500 pounds (200kg) per year; Washington land- ings for the same penod ranged from 13,000 pounds (6tonnes) in 1989 to 6,700 pounds (3ton- nes) in 1992, Alaska reported landings of 464,000 pounds (210tonnes) for 1989. These values do not include confidential data; however, landings of P. caurinus continue to fluctuate and represent à small 96 of the US scallop fishery (NMFS). Gear utilized ranges from old shrimp trawls to typical east coast drag (Bourne,1990) and methods of management vary. Alaska has had а seasonal restriction (June 1- March 31) in some areas, area closures and gear regulations. Many regulations were designed to protect crab resour- ces (Bourne, 1990). Minimum ring size on drags must be 4inches (10cm) inside diameter (some arcas permit use of a 3inch (7.5cm) ring) and trawls have been eliminated from the legal gear restrictions. Washington regulates its fishery bv gearsize and mesh or ring size; Oregon by limite: entry, gear and mesh or ring size; and California management is by permits (Bourne, 1990),

PiNK SCALLOP, CHLAMYS RUBIDA SPINY SCALLOP, CILAMYS HASTATA

Pink and spiny scallops are small and co-exist in discontinuous populations along the US west coast from Alaska to California (Fig.9); they are often referred to as 'singing scallops'. They arc slow-growing, rarely attaining shell heights greater than 3.5inches (8em). These species sup- port a small commercial fishery in Washington and landings аге small (Fig. 10), The small size of these scallops has encouraged a market for whole scallops, often consumed steamed as one would eat mussels or clams, This is a dangerous venture given the paralytic shellfish toxins in the region and ability of scallops to concentrate and retain these Loxins for extended periods of lime (Shum- way & Cembella, this memoir),

Fishing is by small drags or diving (Bourne, 1990) and the fishery is regulated by gear and mesh size in Washington.

AQUACULTURE AND ENHANCEMENT

During 1920-1926, William Firth Wells car- ried out some bivalve culture investigations which he reported in his annual reports tothe New York State Conservation Commission. Besides propagating the easier oyster, Crassostrea vir- ginica, he cultured quahogs, Mercenaria mer-

294

60°

Alaska

50°

Chlamys rubida (pink scallop)

MEMOIRS OF THE QUEENSLAND MUSEUM

Columbia

Chlamys hastata (spiny scallop)

40°

30°

160° 150°

Pacific Ocean

140° 130° 120°

FIG.9. Distribution of Pacific coast scallop species: weathervane scallop, Patinopecten caurinus; pink scallop, Chlamys rubida; spiny scallop, Chlamys hastata. After Bourne 1990).

cenaria, soft clams, Mya arenaria, mussels, Mytilus edulis and bay scallops, Argopecten ir- radians (State of New York Conservation Department,1969). Wells used a milk separator to clarify his culture water and to collect larvae from cultures for transfer. One of the earliest species he cultured was the bay scallop. It was perhaps the first bivalve cultured in the manner similar to what we think of today as aquaculture (late Joseph Glancy, pers. comm.).

Most scallop culture in the US now utilizes the

bay scallop, A. irradians irradians or A. irradians concentricus. The species is characterized by rapid growth, high fecundity and a high market value (Castagna,1975; Castagna & Duggan, 1971,1972). The hatchery technology is well known and successful manipulation of adult scal- lops in the hatchery can provide a sexually mature spawning stock throughout the year (Sastry & Blake,1971; Barber & Blake,1981). A number of companies have attempted to culture scallops but have not been economically successful and there

US SCALLOP CULTURE AND ENHANCEMENT

Whole Weight (tonnes) ü Meat Weight (tonnes)

79 7? ТЕ 19 Mo 8! B2 а BÀ BS 5% BT

0а 4g 9 91

wal OREGON же 2000 1750 1500 (250 1020 720 50 30

76 77 78 70 50 81 00 83 HÀ 8 G5 B7 HÀ M5 30 3j 3c

YEAR

FIG.10. Landed value of weathervane scallops, Patinopecten caurinus (Bourne, 1990; NMFS, pers. comm. ).

is no profitable, private aquaculture industry for bay scallops in the US (Rhodes, 1990; pers. obs.).

This species has been successfully cultured in China (F. Zhang, K. Chew, pers. comm.) and the product is being imported to the US. Recent un- explained mortalities have been attributed to in- sufficient genetic diversity and new broodstock has been supplied by Canadian sources (Atlantic Fish Farming, February 27,1993).

A few companies have been involved in enhan- cement programs, also utilizing bay scallops. Per- haps the most successful is carried out by the Martha’s Vineyard Shellfish Group which is a consortium of 5 towns (Chilmark, Gay Head, Oak Bluffs, Tisbury and West Tisbury) on Martha’s Vineyard off the coast of Massachusetts. This group, using a number of federal and state grants, built a solar-assisted hatchery to produce А. ir-

295

POUNDS OF MEATS ( x 1000.)

FIG.11. Commercial landings of bay scallops in New York (from Tettelbach & Wenczel,1990).

radians irradians and clams, Mercenaria mer- cenaria (Karney,I978). Their hatchery methods are standard except that the seawater is partially warmed in a passive solar system within the solarium-type building. The post-set scallops are held in an indoor, semi-closed nursery system supplemented with cultured algae until the juveniles are 3—5mm high, then moved out to a small embayment in burlap bags with a brick anchor and a plastic cola bottle inside the bag for a float. Several hundred to a few thousand seed are placed in each bag which is then anchored over the submerged vegetation in the bay, This allows the seed to grow to a size that offers sanctuary from some predators before the bag rots away allowing the juveniles to escape a few at a time and spread into the vegetation (В.С, Karney pers. comm.). Each township has legal jurisdic- lion over its own shellfish waters, sale of harvest- ing licenses and control of the harvest. Each township supporting the hatchery buys seed at about cost for replenishment or enhancement of an area. The effect of scallop enhancement has been to add a degree of stability to the harvest in the area that 15 seeded (Karney,1978).

Another enhancement program was carried out in the Long Island Sound area after heavy mor- talities of native scallops caused by a picoplan- kter, Aureococcus annophagefferens. Extensive reseeding of hatchery-reared scallops was in- itiated in the Peconic Bays by the Long Island Green Seal Committee in 1986 (Tettelbach & Wenczel,1993). In the following two years, seed scallops (A. irradians) were purchased from a number of hatcheries and released in selected areas to enhance or replace the natural popula- tions which were lost. The effects of this enhan- cement effort Were not quantified in all areas, but

MEMOIRS OF THE QUEENSLAND MUSEUM

TABLE 6, Historic number of vessels, number of landings, Janded weight of shucked meats, price per pound, exvessel value, landings per vessel, and exvessel value per vessel for the weathervane scallop fishery in Alaska during 1967-1991. All data for 1967-1968, and prices and exvessel values for 1967-1975 and 1979 were taken from Kaiser 1986); all other data were summarized from fish tickets. The 1991 data are preliminary. In years when only one or two vessels participated in à fishery, the harvest statistics are confidential. (from Kruse et

al.,1992)

: EM

1970 7 wu | s |

1972 5 эз | 5s |. as | 1974 3 29 504,438

435,672 1976 1977

54 525,508

anumber of scientists involved in this experiment initially believed the effects of the seed planting were minimal (Bricelj et al.,1987; Tettelbach & Wenczel,1993), Krause (1992), however, showed about 25% of the scallops in the area were survivors of those released. Subsequent reseeding efforts were further hampered by the shell-boring parasite, Polydora sp. and another “brown tide". While enhancement efforts are encouraging, the New York bay scallop fishery is precarious.

In the northeast there is some experimental culture of the sea scallop, Placopecten magel- lanicus at the hatchery on Beal Island, Maine. The technology for culturing this species has already been established in Canada; however aquaculture of this species has not been attempted in the US

BHEIES Eu |e Vessels Lundingy are Value ($) чм А | | 168 | 19 | ms | втв | oss | 125,678 | 88277 | 75036 | EN NEN EN mea | a imes | CNET | зт | 1440338 | — 100 — | 1440438 | 205,763 | 205763 | | 60 | suas | ros | 9775709 | 186230 | 195542 | | és | 61167034 | 115 | 1342089 | 233407 | 268418 |

ws | a [| s | азво | 140 |

——C st

1981 924.441 | aos | 3743986 | 51358 | 207999 | € n ERE EE | аз | кимыл зз ER а ъс кын. 488 947,286 32,353 Omm. 881

1984 | 10 | в [| змат | 447 | 1142282 | 38982 | 174248 | | ws | 9 | s | 67292 | 312 [| 2019551 | 71920 | 224395 |

| is | o | se | 6862 | 366 | 2498397 | 75847 | 277000 | | 1з | 3 | ss | {mos | 338 | 1970685 | 145760 | 492671 |

1988 — 47 341.070 297,584

mr нагна DRY 1m m 5016724 | 165405 | 557,414 | gm | e | ma | ii3564 | 1,546,231 6,045,763 | 220,890 | 863,680

Landings Value ($) (lbs) per per Vessel , Vessel

Confidential

655,769 168,146 218,590

609,94] 108,918 152,485 Confidential Confidential

Confidential

3 68 1 ЭМ, 201 m 085 276,314

4,228,334 189,442

3.72 704,722

(Culliney,1974; Naidu & Cahill,1986; Beninger, 1987; Mallet, 1988). The present study plans to test grow the scallops in near-bottom containers, either bags or cages. Some of these will be placed near salmon pens to see if the efflnents will en- hance growth rates. Initial studies by Belle (pers. comm.) indicate that increased growth rates can be realized in oysters and sea scallops grown in lantern nets suspended near salmon pens.

On the US Pacific coast, there has been some previous interest in culturing the rock scallop, Crassadoma gigantea (Jacobson, 1977; Leighton & Phleger,1977,1981; Leighton, 1979a,b; Moni- cal, 1980; Cary et al.,1981,1982) and there is an experimental culture program in Washington for this species (Chew, pers. comm.). A project was

US SCALLOP CULTURE AND ENHANCEMENT

TEW en Moning Bhais

= Crores бал vimm Morir E Fjernes ДТ me / Уу VU уву пагы 4, їїш/ п! Маты авап D 20 РА Мид туго э d ару onan = = 5 = w $ 3 Ss 2 T ы; 9 6 ' 2 a 4 ^ EM 7 50 H* 100 110 120 190 4%)

Миа Haight (mins)

FIG.12. Regression analyses for adductor weight vs, shell height for Placopecten magellanicus from various geographic locations (Schick et al. 1987).

initiated in Alaska in 1987 to determine the feasibility of culturing weathervane scallops utilizing natural spat sets. In the Washington state hatchery, after preliminary culture experiments on Pecten caurinus and C. gigantea (Olsen, 1981, 1983), C. gigantea was grown and released in an atiempted enhancement program (Olscn,1984); however, the numbers released were insufficient to follow. Efforts have also been made to collect juvenile pink and spiny scallops from natural spat sets; however these species are too small and too slow growing to support an economical culture operation (Bourne, 1990),

Except for small, sporadic releases of Argopec- ten or Crassadoma over the years, there are no major scallop enhancement programs in the US. Scallop culture (mainly research) is underway in Maine, Massachusetts, New York and Virginia; however, itcan hardly be considered a significant or economically feasible activity.

ACKNOWLEDGEMENTS

We are indebted to Barbara O'Bannon, Robert Morrill, and John Bishop of the National Marine Fisheries Service for landings data and helpful discussions. Thanks also to Gordon Kruse for making Table 6 available. Jan Barter prepared the tables and Jim Rollins drafted the figures.

LITERATURE CITED

ANONYMOUS 1992, Status of fishery resources off the northeastern United States for 1992, NOAA

Technical Memorandum NMFES-F/NEC-95; l- 133

BENINGER, P.G, 1987, A qualitative and quantitative study of the reproductive cycle of the giant scal- lop, Placopecten magellanicus, in the Bay of Fundy (New Brunswick, Canada), Canadian Jour- nal of Zoology 65: 495—498.

BARBER, B.J, & BLAKE, N.J. 1983. Energy storage and utilization in relation to gametogenesis in A, irradians concentricus (Say). Journal of Ex- perimental Marine Biology and Ecology 52; 121— 134.

BLAKE, N.J, & MOYER, M.A. 1990. The calico scal- lop, Argopecten gibbus, fishery of Cape Canaveral, Florida. Pp, 00-00. In S,E, Shumway, (ed,), ‘Scallops: biology, ecology and aquaculture’, (Elsevier; New York).

BOURNE, N. 1990. West coast of North America. Pp.925-939, In S.E. Shumway, (ed.), ‘Scallops; biology, ecology and aquaculture’. (Elsevier: New York).

BRICELJ, М., BPP, J. & MALOUF, R. 1987. Inter- specific variation in reproductive and somatic growth cycles of bay scallops Argopecten it- radians, Marine Ecology Progress Series 36: 123- 189,

CARY, S.C., LEIGHTON, D.L. & PHLEGER, C.F, 1981. Food and feeding strategies in culture of Jarval and early juvenile purple-hinge rock scal- lops, Hinnires multirugosis (Gale). Journal of the World Mariculture Society 12: 156-169.

CASTAGNA, M, 1975, Culture of the bay scallop, Argopeeten irradians in Virginia. Marine Fisheries Review 37: 19-24,

CASTAGNA, M, & DUGGAN, W.P. 1971. Reanng of the bay scallop, Aequipecten irradians. Proceed- ings of the National Shellfisheries Association 61: 80-85,

CASTAGNA, M. & DUGGAN, W.P. 1972, Maricul- ture experiments with the bay scallop, Argopecten irradians, in waters of the seaside of Virginia. Bulletin of the American Malacological Union 37:

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REPRODUCTION AND RECRUITMENT IN THE DOUGHBOY SCALLOP, CHLAMYS

ASPERRIMUS, IN THE D'ENTRECASTEAUX CHANNEL, TASMANIA WILL ZACHARIN

Zacharin, W. 1994 08 10: Reproduction and recruitment in the doughboy scallop, Chlamys asperrimus, inthe D'Entrecasteaux Channel, Tasmania. Memoirs of the Queensland Museum 36(2); 299-306. Brisbane. ISSN 0079-8835,

Doughboy scallops in the D'Entrecasteaux Channel can grow to a shell height of 110mm. Reproductive output in this population displays both temporal and spatial changes. The highest gonosomatic index recorded was 45% for a doughboy of 105mm. The number of mature eggs released in the 90-95mm size class was significantly different between two annual peak spawnings and there is evidence for secondary or partial spawnings. Recruitment monitoring through the deployment of spat collectors and sampling of the populations suggests that hydrodynamic influences play an important role in recruitment success.

Will Zacharin, Sea Fisheries Division, Department of Primary Industry and Fisheries, GPO

Box 619F, Hobart 7001, Tasmania; 20 June 1994.

The doughboy scallop, Chlamys (Mima- chlamys) asperrimus (Lamarck,1819), is an abundant benthic bivalve found throughout southern Australia. Large populations extend over wide areas in Bass Strait, and a commercial and recreational dredge fishery for the species has operated irregularly in the D'Entrecasteaux Channel in southeastern Tasmania since the 1930's (Perrin & Croome,1988). An annual recreational dive fishery in the D'Entrecasteaux Channel is now the only remaining fishery.

For such a prominent member of the southern Australian benthic community, surprisingly little information exists in the scientific ljterature on the life history of the species. Larval and juvenile development of the doughboy were studied by Rose & Dix (1984); observations on epizoic sponge associations with the doughboy have been reported by Pitcher(1981) and Pitcher & Butler (1987), and some factors affecting mortality were described by Chernoff (1987). However, no studies have been conducted on growth, reproduction or population dynamics.

This study describes the reproduction and recruitment of the doughboy scallop in the D’- Entrecasteaux Channel, a semi- enclosed inshore waterway in southern Tasmania (Fig. 1).

MATERIALS AND METHODS

A sample of 10-50 doughboys was collected from the same population in Simpson's Bay at 14 day intervals over 28 months (1 July 1988-27 November 1990), In the laboratory the animals were measured (shell height to the nearest 0.1 mm) and total somatic and gonad tissue were

weighted to the nearest 0.1g. Sex was determined according to colour of the gonad, males being white and females orange. Gonosomatic Index (GST) was calculated as a ratio of gonad weight to somatic tissue weight. A significant decrease in the index was considered to be an indication of spawning (Dredge,1981; Sause et al, 1987; West, 1990), The terminology of stages in the gonad reproductive cycle was based on that of Pecren fumatus (Sause et al.,1987), Chlamys varia (Shafee & Lucas.1980) and Amwsium ballori (Dredge, 1981).

A fecundity index was developed using an in- direct method, in which the difference in gonad weight of mature female scallops immediately pror to spawning and after spawning was calcu- lated. This weight loss on spawning can be used as an index of the number of ova released from the gonad. The underlying assumptions are that mature ova prior to spawning have the same mass from year to year, and ova mass is the same across all size classes.

Regular surveys of doughboy populations in the D’Entrecasteaux Channel have been con- ducted by the author since 1985 to monitor recruitment. Between 1985 and 1988, 110-119 random stations within each statistical area were sampled using a 2.5m wide tnothed scallop dredge (Zacharin, 1986,1987,] 988). Since 1989, scallop surveys have been conducted by diving, to more accurately sample doughboys in the size range 30—40mm (1+ animals) (Zachann, 19912,b; Zacharin et al., 1990).

As scallops are usually distributed at low den-

sities over Jarge areas and at high densities form- ing ‘commercial beds” over small areas, sampling

300 MEMOIRS OF THE QUEENSLAND MUSEUM

DERWENT

Oyster Cove & Barnes Bay

ISLAND’ Houn River

Simpsons Вау

Adventure Bay

SOUTH

BRUN Y

Банда) Island

ISLAND

FIG.1. D'Entrecasteaux Channel as divided into statistical areas by Fairbridge (1953) for conducting scallop surveys. The same boundaries were used for the dredge and dive surveys between 1986 and 1992. (from Perrin & Croome, 1988)

DOUGHBOY SCALLOP, TASMANIA

28 Sept &%

WRI

4

16 Nov 9f)

/

13 Gel 88 7 Dec 88

4

3 Noy 80

MEAN GONOSOMATIC INDEX I

5 fan 90

d read ї n 74 161 3847 442 539 765 82h

DAYS

FIG.2. Seasonal changes in mean gonosomalic index in the female doughboy scallop from the D'- Entrecasteaux Channel. (Error bars =one standard deviation.).

technique must compensate for this fact. To ad- just for this pattern of distribution, diver surveys were conducted using the following procedure. A number of random sampling points were dis- tributed over an area to give an indication of scallop distribution. Further non-random sam- pling points were chosen based on previous catch history of the area and from reported sightings by divers, Ateach site a 100m transect line weighted with lead and buoyed at each end was deployed parallel to the current, Two divers swam along the transect collecting all scallops within 1m of the weighted line. It is important to deploy the line

301

15 Sepi 88

2 ext RO

pA

7 Dec КА

13 Oct SH

MEAN GONOSOMATIC INDEX

"4

3 Jan 88

n 105 324 450 728 82h

DAYS

FIG.3. Seasonal changes in mean gonosomatic index in the male doughboy scallop from D’ Entrecasteaux Channel. (Error bars=one standard deviation.)

with the current and to swim with the current, as any scallops disturbed by the deployment of the line may move. As scallops tend to swim off the bottom and then free-fall to the substrate the majority are more likely to remain in the transect area if deployment is parallel to the current. The data were assembled as both total size frequen- cies for the whole of the channel area and as size frequencies of scallops in the various statistical areas.

Spat collection was conducted using small orange coloured onion bags with dark monofila- ment mesh filling as a settlement substrate. The

TABLE 1. Description of gonads and the histological condition of the various stages in the annual reproductive cycle of the scallop, Chlamys asperrimus from the D'Entrecasteaux Channel, Tasmania.

Female

Male

(1) Resting Gonad small, flat and yellow brown. Composed of loose connective tissue. Intestinal loop visible.

Ciliated ducts present

(2) Early Slight increase in gonad size. Follicles with primary oogonia or spermatogonia. Clear differentiation of development male and female gonads. Intestinal loop not visible.

(3) Late Gonad increased in volume, tip being tapered. development

Gonad orange. (4) Mature

(5) Spawning Loss of gonad colour.

Gonad volume large with rounded np. Little connective tissue.

Follicle packed with mature irregular polygonal Large number of spermatozoa. Follicles tightly oocytes. acked.

Free space in the centre of the follicles as gametes are expelled. Appearance of more connective tissue.

Gonad white.

(6) Spent

Follicles nearly empty of all gametes. Increase in connective tissue. Phagocytes predominate.

302

(19) (1211)

Gonad Weight (g)

55 60 = 5 ( 75 a0 85 7].

E 5 100 105 (10

Shell Height (mm)

FIG.4, Fecundity index shown as a relationship be- tween shell height (5mm intervals) and gonad weight for mature samples (A) collected on 15 and 28 Sep- tember 1988 and immediate post-spawning samples (B) on 13 and 20 October 1988. Number of scallops shown in brackets.

first spat collectors were deployed on 18 Septem- ber 1988 at various locations throughout the channelarea. Sites were selected where tidal flow was greater around prominent headlands and is- lands. Collectors were observed each month to assess the intensity of spat settlement.

RESULTS

REPRODUCTION

Six distinct stages of development were recog- nised (Table 1). During late summer to autumn (January-March) gonads were completely spent and appeared to be in a ‘resting phase’. Accurate macroscopic identification of sex for the majority of individuals during the ‘resting phase’ proved 10 be impossible.

Fortnightly changes in mean GSI of females and males (Figs 2,3) are interpreted as increases

TABLE 2, Results from spat collectors deployed ad- jacentto Huon Island in the D' Entrecasteaux Channel (statistical area 9) during 1988/89,

Standard deviation

316

| 28/2/89 230 10.43 1.97 21/3/89 226-306 12.65 2.69 |

MEMOIRS OF THE QUEENSLAND MUSEUM

(1)

Пипа Weight (2l =

(8) 119001}

i (B)

© d c чї € л c V1 c Un wy б MD p or o6 c с б

[ШЇ] 105

110

Shell Height (mm)

FIG.5. Fecundity index shown as a relationship be- tween shell height (5mm intervals) and gonad weight from mature samples (A) collected on 4 and 12 Oc- tober 1989 and immediate post-spawning samples (B) on 2 16 November 1989, Number of scallops shown in brackets.

in gonad weight due to follicular development and production of gametes; rapid decrease in gonad weight in September-October was indica- tive of spawning. The differences in gonad weights (being an index of ova number) for grouped samples (Smm) indicated a significant increase in ova number for the older and larger