945 Scallops: Biology, Ecology andAquaculture S.E.Shumway andG.J. Parsons (Editors) © 2006 ElsevierBV. All rights reserved.

Chapter /7

Bay Scallop and Calico Scallop Fisheries, Culture andEnhancement in Eastern North America

NormanJ. Blake and SandraE. Shumway

17.1 INTRODUCTION

Scallops are commercially important shellfish worldwide (Table 17.1) with the average total catch between 1988 and 1997 at 522,894 pounds of meats (FAa 1997). Five species (sea scallop, Placopecten magellanicus; Icelandic scallop, Chlamys islandica, calico scallop, Argopecten gibbus; bay scallop, Argopecten irradians; weathervane scallop, Patinopecten caurinus) contribute to the major wild fisheries in North America with minor fisheries for two other species (pink scallop, Chlamys rubida and spiny scallop, Chlamys hastata).

Aquaculture and enhancement efforts are still limited activities in North America but world aquaculture of all scallops exceeds 1.7 million metric tonnes (O'Bannon 1999). Where scallop aquaculture activities do occur in North America, they contribute substantially to the 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 and comprise about 40-80% of the total United States supply (Table 17.2).

This chapter is intended to present an overview of calico and bay scallop fisheries, aquaculture and enhancement efforts in eastern North America. Sea scallops are covered in Chapters 15 and 16 and west coast species are covered in chapter 18.

17.2 FISHERIES

17.2.1 Bay Scallop, Argopecten irradians

/7.2././ Distribution

The bay scallop, Argopecten irradians (Lamarck), occurs in the shallow «10 m), protected estuarine habitats along the east coast of the United States (Fig. 17.1) from Cape Cod, Massachusetts to Texas (Clarke 1965). Three subspecies have been described based upon shell morphometries (Waller 1969). The northern subspecies, Argopecten irradians irradians, extends from Cape Cod to approximately New Jersey and Maryland where it may hybridise with the southern bay scallop, Argopecten irradians concentricus (Clarke 1965). Populations of the southern bay scallop of sufficient size to harvest become discontinuous about North Carolina. It is absent along the Georgia coast (Walker et al.

Table 17.1 '0... ov

Nominal landings (MT) of major scallop species and % contribution to global production byyear(Scuree FAO).

Species 1988 1989 1990 1991 1992 1993 1994 1995 x Argopecten gibbus 121,720 67,330 11,220 0 0 0 74,325 10,003

(Calico scallop) 14% 8% 1% 0% 0% 0% 4% 1% x Argopecten irradkms 2,329 1,360 2,596 2,062 1,564 2,670 524 1,593

(Atlantic bay scallop) 0% 0% 0% 0% 0% 0% 0% 0% Argopecten purpura/us 7,828 4,012 2,212 2,920 7,758 7,715 12,073 11,808

(Peruvian calico scallop) 1% 0% 0% 0% 1% 1% 1% 1% Argapecten circuiaris 9,220 12,520 29,501 19,438 5,350 5,943 8,611 1,270

(Pacificcalico scallop) 1% 1% 3% 2% 0% 0% 1% 0% Chlamys islandica 10,059 10,772 12,117 11,107 21,269 16,798 17,230 23,570

(Iceland scallop) 1% 1% 1% 1% 2% 1% 1% 1% Chlamys apercu/aris 15,613 14,533 16,832 14,324 16,089 15,325 10,576 8,086

(Queen scallop) 2% 2% 2% 2% 2% 1% 1% 0% Patlnopecten yessoensis 466,530 502,163 570,939 558,683 742,792 1,196,713 1,300,314 1,423,869

(Japanese scallop) 53% 59% 63% 64% 69% 81% 79% 85% x Patinopecten caurinus 961 1,398 2,415 3,649 6,884 6,224 4,944 1,950

(weathervane scallop) 0% 0% 0% 0% 1% 0% 0% 0% Pecten maximus 15,962 12,656 12,517 15,159 21,391 20,598 25,158 23,657

(Great Atlantic scallop) 2% 1% 1% 2% 2% 1% 2% 1% Pecten jacobeus 4 I I 0.5 0.5 202 308 23

(Great Mediterranean scallop) 0% 0% 0% 0% 0% 0% 0% 0% Pecten novaezelandiae 5,784 4,264 4,504 8,256 10,040 8,928 9,088 14,160

(New Zealand scallop) 1% 0% 0% 1% J% 1% 1% 1% x Plocopecten magellanieus 193,487 206,898 217,153 211,132 192,822 143,921 146,032 121,230

(Sea scallop) 22% 24 24% 24% 18% 10% 9% 7% otherPectinidac 32,863 18,117 24,041 28,949 46,014 53,577 46,230 38,843

4% 2% 3% 3% 4% 4% 3% 2% World Totals 882,360 856,024 906,048 875,679 1,071,973 1,478,614 1,655,413 1,680,062

x Species fished commercially in the United Slates.

Table 17. I continued

Species 199~ ~ ~ 1999 2000 _~QOI Average x Argopecten gibbus 0 o o o o o 20,328

(Calico scallop) 0% 0% 0% 0% 0% 0% 2% x Argopecten irradians 230 452 690 216 154 30 1,176

(Atlantic bay scallop) 0% 0% 0% 0% 0% 0% 0% Argopecten purpuratus 12,275 15,806 41,041 52,394 33,125 28,99\ 17,140

(Peruvian calico scallop) 1% 1% 3% 3% 2% 2% 1% Argopecten circu/aris 17,300 2,330 2,729 1,864 6,287 3,227 8,971

(Pacific calico scallop) 1% 0% 0% 0010 0% 0% 1% Chiamys is/andica 22,752 24,673 18,946 12,018 13,471 9,469 16,018

(Iceland scallop) 1% 1% 1% 1% 1% J% 1% Ch/amys opercularts 7,234 11,489 14,633 15,860 14,949 20,511 14,004

(Queen scallop) 0% 1% 1% 1% 1% 1% 1% Patinopecten yessoensis 1,541,660 1,523,784 1,150,430 1,234,235 1,442,970 1,489,403 1,081,749

(Japanese scallop) 87% 86% 82% 81% 81% 79% 75% x Patinopecten caurinus 2,372 2 3,228 2,642 2,012 1,052 2,838

(weathervane scallop) 0% 0% 0% 0% 0% 0% 0% Pecten maximus 31,955 36,072 35,908 36,626 37,851 30,809 25,451

(Great Atlantic scallop) 2% 2% 3% 2% 2% 2% 2% Pectenjacobeus 52 95 50 68 570 150 109

(Great Mediterranean scallop) 0% 0% 0% 0% 0% 0% 0% Pecten novaezelandiae 5,080 18,848 4,592 6,152 2,912 6,792 7,814

(New Zealand scallop) 0% 1% 0% 0% 0% 0% 1% x Placopecten magel/anicus 109,382 102,028 99,432 131,962 196,993 254,196 166,191

(Sea scallop) 6% 6% 7% 9% 11% 14% 183% other Pectinidae 23,896 26,438 28,872 27,250 26,940 34,202 32,588

1% 2% 2% 2% 2% 2% 3% World Totals 1,774,188 1,762,017 1,400,551 1,521,287 1,778,234 1,878,832 1,394,377

x Species fished commercially in the United States.

~

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Table 17.2

US supply of scallops, 1976-2000 (SourceFAO).

Year Import 1976 11,455 1977 13,511 1978 12,867 1979 11,410 1980 9,473 1981 11,896 1982 9,462 1983 15,549 1984 12,372 1985 19,067 1986 21,734 1987 15,392 1988 14,533 1989 18,601 1990 18,156 1991 13,438 1992 17,622 1993 23,613 1994 25,766 1995 21,981 1996 26,684 1997 27,366 1998 24,132 1999 20,231 2000 24,530

Export Total 0 11,550 0 13,561 0 14,279 0 11,326 0 9,743 0 16,572 0 11,504 0 9,591 0 24,039 275 10,508 370 6,281 385 8,897 303 10,348 1,174 7,049 3,272 5,350 3,197 3,456 1,634 3,166 1,884 4,961 2,755 5,217 2,707 5,378 2,808 8,073 4,501 7,340 3,484 9,374 3,367 6,640 4,164 8,774

1991) and from the east coast of Florida (unpub. data). It reappears on the southwest coast of Florida in Florida Bay and continues north along the west coast to Pensacola. Although not common, the southern subspecies reportedly is found as far west as Louisiana (Waller 1969; Broom 1976). The third subspecies, Argopecren irradians amplicostatus, occurs in the western Gulf of Mexico (Waller 1969). The degree to which these subspecies are physiologically different is not well understood (Bricelj et al. 1987) but Blake et al. (1997) have shown that there are significant genetic differences.

17.2.1.2 Biology

Bay scallops are functional hermaphrodites, which reproduce essenlially once during their 12-24 month life span. Spawning is largely catastrophic, although the northern populations are more synchronous than the southern subspecies (Barber and Blake 1991).

949

The northern subspecies from New York spawn from June through August (Bricelj et al. 1987) while the Massachusetts populations spawn May through July (Taylor and Capuzzo 1983). In North Carolina, bay scallops spawn from July through August (Sastry 1968). On the west coast of Florida, the southern subspecies spawns in early August in the north (Sastry 1961) and October in the south (Barber and Blake 1983). Little has been reported about the spawning of the subspecies A. irradians amplicostatus in the western Gulf of Mexico. See Chapter 6 for a more detailed discussion of scallop reproduction.

The planktonic larval stage lasts 12-14 days (Sastry 1965), and it is during this planktonic stage that the larval distribution and eventual recruitment may be controlled by the hydrodynamics of the estuary (Eckman 1987). As the larvae metamorphose, the prodissoconchs (\ 90 urn) typically attach to blades of seagrass. Growth during the winter is slow but by early spring scallops of20-25 mm can be seen on the seagrass (Barber and Blake 1983). By late spring scallops become unattached and settle to the bottom at which time growth becomes rapid. Scallops of 40-50 mm occur by summer and may reach 60-90 rom by early winter (approximately 16 months of age). Growth is continuous in the Florida subspecies even at 33°C, only 2°C below the upper lethal temperature of the

IArgopecten irradians irradians

" - Argopecten if!adians ~ _ concentncus ~

_ Argopeeten gibbus D

Figure 17.1, Distribution of scallops (Argopectensp.) in eastern North America.

950

adults (Sastry 1961). Natural mortality after 12 months of age is high due to senescence, and only a few survive into the winter months of their second year.

17.2.1.3 Fishery

Landings are highly variable among years and among the various sections of the eastem United States (Table 17.3). The populations are dependent upon natural recruitment for continuation, although some enhancement efforts have been attempted. In 1985, bay scallop populations in the northeast were decimated by blooms of a previously unknown microalga, Aureococcus onophagejferens ("brown tide") (Tettelbach and Wenczel 1993). Three successive years of algal blooms resulted in virtually all-native stock in the Peconic Bays and the New York fishery being essentially eliminated. In addition, eelgrass beds were also depleted, thus reducing the total area of suitable habitat for scallop settlement. Landings for 1998 were 105,000 pounds of meats valued at $US 368,000 (Fig. 17.2). This represents an increase of 33,000 pounds (46%) and $58,000 (19%) compared with 1997 (O'Bannon 1999). The average ex-vessel price per pound of bay scallop meats was $3.50 in 1998 compared with $4.31 in 1997. Meat counts range between 50 and \00 per pound. Total catch and landed values from 1950-1999 are presented in Table 17.3 and Fig. 17.2.

Commercial fishing records for A. irradians date back to 1858 (Ingersoll \ 886) and the introduction of the dredge in 1874. Commercial fishing for A. irradians is strictly limited and there is a large recreational fishery. In most areas, harvest is usually limited to the months of August-December. The bay scallop fishery is a protected resource throughout the range of the species. Commercial harvest of the species was prohibited in Florida waters in \995.

Scallops are usually collected by diver, handpicking 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 presently harvested. Catch limits are determined on a season-by-season basis by fisheries officials in accordance with population fluctuations (Rhodes 1990; 1991).

Table 17.3

Historical catch statistics (total catch by regions) for bay scallops, (Argopecren sp.) for the period 195()-1999 (numbers in thousands). (NMFS, pers.comm.).

Year New England MiddleAtlantic South Atlantic GULF Grand Total

Lbs s Lbs s Lbs s Lbs s Lbs $

1950 1,376 1,130 27 32 72 39 125 63 1,600 1,264 1951 1,253 959 101 121 183 96 252 161 1,789 1,337 1952 1,188 913 182 255 254 126 210 48 1,834 1,342 \953 2,397 1,222 162 102 65 33 229 53 2,853 1,410 1954 987 688 127 110 52 26 43 10 1,209 834 1955 1,070 837 226 210 78 39 223 53 1,597 1,139

951

1956 433 433 464 426 125 63 278 70 1,300 992 1957 1,230 880 674 447 109 37 315 91 2,328 1,455 1958 1,013 680 688 413 169 58 401 75 2,271 1,226 1959 591 700 385 386 128 51 82 19 1,186 1,156 1960 1,063 759 843 674 69 27 56 14 2,031 1,474 1961 704 671 862 621 106 42 36 14 1,708 1,348 1962 1,425 1,081 1,353 851 168 67 213 68 3,159 2,067 1963 391 492 577 404 321 122 228 59 1,517 1,077 1964 466 595 1,063 886 340 173 18 14 1,887 1,668 1965 459 562 982 766 379 196 39 24 1,859 1,548 1966 880 1,076 492 408 399 184 9 4 1,780 1,672 1967 455 579 248 258 387 211 7 5 1,097 1,053 1968 491 776 218 374 639 422 143 122 1,491 1,694 1969 1,172 1,592 249 377 613 383 80 61 2,114 2,413 1970 1,101 1,704 365 470 130 91 104 56 1,700 2,321 1971 2,063 3,531 144 234 60 42 48 39 2,315 3,846 1972 1,776 3,407 93 215 128 110 35 40 2,032 3,772 1973 694 1,462 230 467 37 33 53 63 1,014 2,025 1974 567 1,014 694 872 220 199 16 18 1,497 2,103 1975 1,054 2,568 444 713 135 105 14 16 1,647 3,402 1976 890 1,973 438 816 248 194 14 24 1,590 3,007 1977 1,044 3,085 199 489 257 509 46 58 1,546 4,141 1978 1,521 4,982 280 837 221 393 49 91 2,071 6,303 1979 1,382 5,967 346 1,243 193 514 62 137 1,983 7,861 1980 1,356 6,671 431 1,840 328 1,107 II 29 2,126 9,647 1981 964 4,630 244 891 189 656 22 62 1,419 6,239 1982 2,022 8,949 500 1,809 137 352 13 35 2,672 11,145 1983 1984

1,083 808

6,491 4,573

167 279

992 1,264

205 384

509 876

22 10

75 26

1,477 1,481

8,067 6,739

1985 958 5,812 174 828 456 1,072 4 10 1,592 7,722 1986 509 3,797 13 65 306 838 27 86 855 4,786 1987 341 2,813 (2) 3 155 501 19 80 515 3,397 1988 530 3,339 (2) 2 39 73 39 73 608 3,487 1989 215 1,494 2 22 84 214 57 162 358 1,892 1990 254 1,683 II 132 62 128 56 204 383 2,147 1991 191 1,363 16 117 45 100 0.2 0.6 252 1,580 1992 569 4,079 25 182 22 54 2 I I 618 4,326 1993 145 1,502 15 143 153 365 9 37 322 2,047 1994 I I 272 1,765 73 133 0 0 346 1,899 1995 8 66 26 203 201 401 0 0 235 670 1996 1 3 I 0.4 29 113 0 0 31 116 1997 0 0 7 66 64 214 0 0 71 280 1998 0 0 2 22 103 289 0 0 105 311 1999 0 0 6 96 30 103 0 0 36 199

952

12

10

8

'" 6c:: ~

~ 4

2

0

o

__ Pounds landed 0:: ··0 .. $ Value

oo '.0 .'

o 6 o

o o

i:P

!9Cbo '. o

1940 1950 1960 1970 1980 1990 2000 2010

Year

Figure 17.2. eomm.).

Landings and value of bay scallops, Argopecten irradians, Data from NMFS (pers.

17.2.2 Calico Scallop, Argopecten gibbus

17.2.2.1 Distribution

The calico scallop, Argopecten gibbus, is largely restricted to the sub-temperate and tropical waters of western North Atlantic (Fig. 17.3) with the major stocks distributed from Cape Hatteras, North Carolina to the Cape San BIas area of the northeastern Gulf of Mexico (Waller 1969). Calico scallops have also been collected from the Greater Antilles, Bermuda, and the western portions of the Gulf of Mexico (Waller 1969) but stocks of commercial importance have not been reported from these areas. At least one other species, Argopecten circularis, is commonly called a calico scallop and is harvested in the Republic of Panama.

Argopecten gibbus, inhabits the relatively shallow waters of the continental shelf and upper slope out to reported depths of 370 m (Waller 1969). Major commercial stocks along the Atlantic and Gulf coasts are usually located in depths of20-50 m on hard sand bottom.

953

50 -,---------------------------,

40 ~ Pounds landed ·0·· $ Value

30

'" o ~ 20 ~

10

o

1970 1975 1980 1985 1990 1995 2000 2005

Year

Figure 17.3. Landings and value of calico scallops. Argopecten gibbus. Data from NMFS (pers. comm.)and Florida Marine Research Institute, Fishery Dependent Monitoring Program.

17.2.2.2 Biology

The calico scallop, like the bay scallop, is a functional hermaphrodite. The species exhibits two spawning periods during each calendar year when optimal environmental conditions occur (Moyer and Blake 1986). The first and predominant spawn of the calendar year occurs in late spring from April to June. This follows the accumulation of gonadal reserves during the winter months. When spawning does occur it is rapid and often complete. A large percentage of any subpopulation normally spawns over a 1-3 week period.

The second reproductive cycle of the calendar year begins with an accumulation of gonadal reserves in July and August with spawning occurring in late summer to early autumn. The "fall spawn" apparently occurs only when environmental conditions are optimal and does not occur every year. Only a portion of the total population is involved in this minor spawn; however, the "fall spawn" appears to be important to the maintenance of the commercial stocks into thespring and summer months.

954

The individual scallop normally reproduces for the first time at an approximate age of either 6-12 months depending upon season of birth and the presence or absence of a fall spawn. Age, however, appears to be less important than environmental conditions since calico scallops as young as 3 months occasionally spawn. Whether or not there are any differences in the viability of larvae produced by scallops of different ages has not been examined. A scallop will normally spawn either 2 or 3 times during its 18-24 month life span, although the number of scallops reaching a third spawn in usually very low.

Like the bay scallop (Sastry 1968; Blake and Sastry 1979; Barber and Blake 1985; Barber and Blake 1991), the environmental controls for reproduction in the calico scallop include food, temperature, and age (Moyer 1997). The current dynamics in the region of Cape Canaveral may also be important to the maintenance of the population and these variables have received considerable study (Lee and Brooks 1979; Leming 1979; Blanton et al. 1981; Lee and Atkinson 1983). During the summer months, coastal upwelling brings deep Gulf Stream water onto the shelf resulting in lowered bottom temperatures. This nutrient rich, colder water may be important in allowing the scallops to accumulate nutrients rapidly.

Miller et al. (1981) have suggested that the cold water intrusions may have both favourable and unfavourable results. On the favourable side, the intrusion may initiate spawning, provide food through phytoplankton blooms resulting from nutrient-rich water, and provide an optimal temperature range of IS-27°C for survival. The intrusions may be unfavourable if bottom temperatures are lowered below 15°C where mortality may occur.

Growth rates are not constant but vary as environmental conditions change (Blake and Moyer 1991; Moyer 1997). Growth rates of greater than 1.5 mm per week can occur during upwelling events and can drop to 0.3-0.8 mrn per week as bottom water temperatures increase.

Costello et al. (\973) estimated that calico scallops are planktonic for 16 days under laboratory conditions and set at about 0.25 mm shell height. Therefore, Allen (1979) estimated that 10 mm scallops would be about 51 days old and 28 mm in about 3 months. Considering a two-month interval from spawning to 23 mm, a total of 8 months are required for the scallops to reach 38-40 mm, the commercial size desired by the industry (Blake and Moyer 1991). This period could of course be increased or decreased depending upon environmental conditions, particularly bottom water temperatures.

The calico scallop lives a maximum of two years (Roe et al. 1971). However, since post-spawning mortality may be high, only a small percentage of a year class may survive after 18 to 20 months. Roe et al. (1971) estimated monthly mortality rates ranging from 1% to 31% depending upon the age composition of the population. High mortalities may also occur, even in the young of the population, if bottom water temperatures decrease below 15°C (Miller et al. 1981).

In late 1988 and again in 199\, an ascetosporan parasite, Marteilia sp., virtually eliminated the calico scallop population in the vicinity of Cape Canaveral (Moyer et al. 1993). The parasite had not been previously reported in the western Atlantic and the calico scallop population has not rebounded to pre-parasite levels.

955

17.2.2.3 Fishery

The calico scallop, Argopecten gibbus, supports a highly variable fishery (Fig. 17.3) off the coast of Florida and North Carolina. Although the exact locations of commercial stocks vary from year to year, the Cape Lookout, Cape Canaveral, and Cape San Bias areas (Fig. 17.4) are particularly important to the fishery. The North Carolina fishery is small (Table 17.4) and extremely transient (Allen and Costello 1972) but the scallop meats produced are often large for the species and are good quality. The Cape San Bias fishery of Florida is also highly variable and commercial fishing efforts may occur only every 2-3 years and only after other stocks have been depleted.

....

..'

~:';fERAS 35' _ CAPE

LOOKOUT

.... CHARLESTON

ATLANTIC OCEAN

GULF OF MEXICO

85'

ST. AUGUSTINE

'I;;0/ CAPE%CANAVERAL

~, FORT PIERCE

~-'n '.f

•

..&' : .~.

KEY WEST

75'

30'

25'

Figure 17.4. Commercial fishing grounds for thecalico scallop, Argcpecten gibbus (after Blakeand Moyer 1991).

956

Table 17.4

Historical catch statistics (total catch by state) for calico scallops, (Argopecten gibbus) for the period 1976-1999 (numbers in thousands). '(NMFS, pers. comm.)

Year Florida Georgia South North Grand Total Carolina Carolina

Lbs $ Lbs $ Lbs $ Lbs $ Lbs $ 1976 2,269 1,622 0 0 0 0 0 0 2,269 1,622 1977 1,113 837 0 0 0 0 0 0 1,113 837 1978 478 752 87 118 611 803 0 0 1,176 1,673 1979 1,157 1,711 33 45 0 0 43 81 1,233 1,837 1980 0.4 \.0 0 0 0 0 0 0 0.4 \.0 1981 15,171 14,277 0 0 0 0 244 307 15,415 14,585 1982 10,842 11,274 41 41 0 0 0 0 10,883 11,315 1983 9,352 11,556 0 0 0 0 102 179 9,453 11,735 1984 42,742 23,246 0 0 0 0 0 0 42,742 23,246 1985 12,283 11,450 0 0 0 0 0 0 12,283 11,450 1986 1,566 2,861 0 0 0 0 0 0 1,566 2,861 1987 10,933 11,001 0 0 0 0 0 0 10,933 11,00\ 1988 12,039 8,752 0 0 0 0 668 702 12,707 9,454 1989 6,611 7,439 0 0 0 0 336 469 6,946 7,907 1990 874 1,711 0 0 0 0 385 531 1,259 2,241 1991 39 0 0 0 0 0 0 39 1992 200 0 0 0 0 0 0 200 1993 5,307 3,660 0 0 0 0 0 0 5,307 3,660 1994 6,879 4,072 0 0 0 0 0 0 6,879 4,072 1995 945 805 0 0 0 0 0 0 945 805 1996 0 0 0 0 0 0 0 0 0 0 1997 \,545 1,489 0 0 0 0 0 0 1,545 1,489 1998 2,397 2,065 0 0 0 0 0 0 2,397 2,065 1999 3,572 3,411 0 0 0 0 0 0 3,572 3,411

• 1991, 1992 and 1993 values for Florida are from the Florida Marine Research Institute, Fishery Dependent Monitoring Program.

The most significant and persistent commercial stock occurs in the vicinity of Cape Canaveral, Florida. Commercial stocks of calico scallops were first observed off Cape Canaveral in 1960 (Bullis and Cummins 1961 ). Investigations by the Bureau of Commercial Fisheries (now the National Marine Fisheries Service) from 1960 to 1968 showed that commercial concentrations varied greatly along the coast from the St. Johns River near the Florida/Georgia boarder to Fort Pierce, Florida in depths of 19 to 74 m (Bullis and Cummins 1961; Drummond 1969; Cummins 1971; Roe et al. 1971). More

957

recently the most productive beds have been found to be located in 30 to 50 m of water extending from about St. Augustine. Florida to Fort Pierce. Florida. making a harvestable area of about 2.000 square miles (Fig. 17.4).

The calico scallop grows to less than 3 inches and the adductor muscle (meat) is small and white to pink in colour (meat count range 100-300; normally 150-200). Hand­shucking is not economically feasible; thus. even though large stocks of the calicos scallops were known as early as 1949. the species was not harvested commercially prior to automation in the late 1960's.

Although the current commercial fishery began in 1967. significant landings did not begin until 1980 (Fig. 17.3). This was due to an increase in stocks and to the refinement of automated steam processing equipment. The equipment allowed shellstock representing up to 800 gallons of shucked meats to be processed and packaged within an hour.

Calico scallops are fished using a modified Gulf shrimp trawler. Typically a scallop net. similar to a shrimp net. is towed from each side of the boat. Towing time is regulated and the nets must be equipped with "turtle exclusion devices". No culling occurs and unless processing occurs at sea, theentire catch is returned to shore.

Processing begins as the shellstock is removed from the boat deck by a "knuckle boom". The sca\lops are then placed in a "batching hopper" which relays the unsorted load to an automated shaker. The shaker removes the broken and dead shell. sand. and unwanted species. Steam is then used to "shock" the scallop meats and to separate the meat and other tissue from the shell. A series of rollers then eviscerates the sca\lops separating the visceral mass from the adductor muscle. The visceral mass. commonly eaten in other countries. is discarded while the adductor muscle is rapidly cooled in a series of water baths and chill tanks. Quality control includes "hand culling" of any shell fragments or other imperfections before entry into the final series of chill tanks prior to packaging. With the exception of the "hand culling" the entire process can occur without the meats touching human hands and since the product is shipped immediately to a wholesaler or retailer. it can reach the consumer within 24 to 48 hours without being frozen.

The volatile nature of production of this species is clearly demonstrated in Table 17.4 and Fig. 17.3. During the peak in 1984. landings were almost 43 million pounds and reduced to 39.000 pounds in 1991. Annual variations in production of calico scallops impact not only the total catch in the U.S.• they also determine the position of the U.S. among other world sca\lop producers. Landings of calico scallops were 3.572.000 pounds of meats valued at $US 3.411.000 in 1999. This represented an increase of 1.175.000 pounds (33%) and $US 1.346.000 (65%) compared with 1998. All calico scallops were landed in Florida in \998 and 1999. The average ex-vessel price was $0.86 per pound of meats in \998 compared to $0.95 in 1999 (Florida Marine Research Institute. Fishery Dependent Monitoring Program. pers. comm.),

Since stocks of A. gibbus are annual. over-fishing has not been 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 has been attempted by the industry. Fishing efforts are limited until at least 75% of the stock at a particular

958

location reaches a shell height of at least 38 mm, 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 environmental conditions are optimal. Concerns by regulators about the quantity and disposition of by-catch may eventually lead to more formal regulations.

17.3 AQUACULTURE AND ENHANCEMENT

During the years between 1920 and 1926, William Firth Wells carried out some bivalve culture investigations, which he reported in his annual reports to the New York State Conservation Commission. His reports show that besides propagating the eastern oyster, Crassostrea virgtnica, he also cuItured quahogs, Mercenaria mercenaria, soft clams, Mya arenaria, mussels, Mytitus edulis and bay scallops, Argopecten irradians (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 was able to culture was the bay scallop. This was perhaps the first bivalve cultured in the manner similar to what we think of today as aquaculture in the United States (personal communication, Joseph Glancy, now deceased). Most scallop culture in the United States currently utilises the bay scallop, A. lrradians irradians or A. irradians concentricus. No attempts have been made to culture Argopeclen gibbus in the United States because of its small size and the relatively large natural populations.

The high market value of bay scallops combined with rapid growth and short life span of the species has led to the development and refinement of hatchery, nursery, and grow-out techniques (Castagna and Duggan 1971; Castagna 1975; Rhodes and Widman 1980; Mann and Taylor 1981; Karney 1991; Oesterling and DuPaul 1993; Lu and Blake 1997). Using the information about the natural reproductive cycle investigators have used either artificial conditioning and various stimuli to spawn adults for larval production in a hatchery or relied upon the harvest of reproductively mature adults from the natural environment forspawning stock.

Embryonic and larval stages of marine invertebrates are often the most sensitive to the environmental conditions and extreme mortality of the embryos and larvae can occur if a strict environment is not maintained in a hatchery. Temperature, salinity, and food supply appear to be the most important environmental variables regulating the growth and reproduction of the adults as well as the survival and growth of the embryos and larvae. The combined effects of temperature and salinity on the development of embryos and survival and growth of the larvae of the northern bay scallop, A. irradians irradians, was extensively studied by Tettelbach and Rhodes (1981). Only embryos cultured at 20°C­25%. and 25°C-25%. showed a greater than 70% normal development. At salinities greater than or lesser than 25%0, normal development declined markedly. Larval survival of this northern subspecies for 2-5 days after fertilisation occurred over a much wider temperature-salinity range with the optimal combination being 18.7°C and 28.1%0. Maximal larval survival at time of settlement occurred at 20°C-25%.. Lu (1996) has shown that this same temperature and salinity combination is optimum for the Florida bay scallop larvae and juveniles and that maximum growth of Florida bay scallop larvae and

959

juveniles occurs when a food supply of lsochrysis galbana is maintained at a density of 10-40 thousand cells per mL of culture. '

A number of different techniques have been used in hatcheries to maintain larvae and early juveniles. These techniques have included static, aerated water tanks (Castagna and Duggan 1971; Castagna 1975; Karney 1991; Oesterling and DuPaul 1993; Lu and Blake 1996) for early larval development. Sieves suspended in down-flowing aerated conicals (Karney 1991), raceways or troughs fitted with inserts (Oesterling and DuPaul 1993), and plastic strips suspended in aerated tanks (Lu and Blake 1996) have been used for pediveliger and post-set animals. Flow-through upwelling systems (Oesterling and DuPaul 1993) and nylon-meshed bags suspended in the natural environment (Lu and Blake 1997) are two of the more commonly employed techniques for the nursery of early juveniles from 1-8 mm.

For grow-out, Castagna and Duggan (1971) used large pens in order to demonstrate that a market-sized scallop could be attained in 5-7 months. Early releases of juvenile scallops into the natural environment for commercial harvest proved unsuccessful due to heavy predation (Morgan et al. 1980). Rhodes and Widman (1980) utilised Japanese pearl nets and lantern nets to determine the optimum scallop density for maximum growth in Long Island Sound. Oesterling and DuPaul (1993) used polyethylene trays or plastic mesh cages placed directly on the bottom, placed on cinder blocks, or suspended in the water column on a rack system to demonstrate an optimum density of about 500-800 scallops per square meter for attaining a market-size scallop of 40 mm in 7 months, More recently Oesterling (pers. comm.) employed a floating pen system to suspend the plastic cages in the water column.

Heavy mortalities can occur at all three points in the aquaculture process. Pathogens associated with scallop diseases have been reviewed by Leibovitz et al, (1984). Pathogenic Pseudomonas can bloom on the solid surfaces of culture vessels and kill larvae or early juveniles but can be minimised with regular cleaning and water changes (Karney 1991). In the nursery and grow-out stages fouling of the nets or cages can reduce flow rates which leads to reduced growth and increased mortality but this can also be minimised with frequent cleaning (Karney 1991). In the final stages of grow-out, especially during the summer, mortality can occur for unknown reasons (Oesterling, pers. comm.; Lu and Blake 1997) although fouling of the shells by tunicates, barnacles and oysters may be one of the primary causes but frequent cleaning of the shells to decrease the degree of fouling may also lead to mortality.

A number of companies have attempted to culture scallops but have been unsuccessful economically and there is currently no profitable, private aquaculture industry for bay scallops in the United States. Some recent attempts to market the whole bay scallop product to a speciality market have had mixed success due largely to production problems. The best success with the aquaculture of the species has been in China (Ximing et al. 1999) where in 1982, 26 individuals of Argopecten irradians irradians transplanted from the United States were spawned successfully (Fusui Zhang, pers. comm.). Using techniques largely developed in the U.S., the annual bay scallop production in China steadily increased to over 50,000 tons live weight in 1988. The shucked muscles are

960

imported into the U.S. at $2.00 per pound (Zhang 1995). This success can be partially attributed to the low cost of abundant labour as well as to the legal utilisation of the total marine habitat.

A few organisations have been involved in enhancement programs, also utilising bay scallops. Perhaps the most successful program of shellfish enhancement is carried out by the Martha's Vineyard Shellfish Group. This is a consortium of 5 towns (Chilmark, Gay Head, Oak Bluffs, Tisbury and West Tisbury) on the island of 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 bay scallops, A. irradians irradians and clams, Mercenaria mercenaria (Karney 1978). The hatchery methods used at Martha's Vineyard are fairly 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, semi­closed nursery system supplemented with cultured algae until the juveniles are 3-5 rnrn height. 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 found 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 (Karney, pers. comm.). Each township has legal jurisdietion over its own shellfish waters, sale of harvesting 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 is seeded (Karney 1978).

Another enhancement program was carried out in the Long Island Sound area after heavy mortalities of native scallops were observed (see above). The mortality and subsequent recruitment failure was caused by a form of picoplankton, Aureoeoeeus annophagejJerens. Extensive reseeding of hatchery-reared scallops was initiated in the Peconic Bays by the Long Island Green Seal Committee in 1986 (see Tettelbach and 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 populations, which were lost. The effects of this enhancement effort were not quantified in all areas, but a number of scientists involved in this experiment initially believed the effects of the seed planting were minimal (Bricelj et al. 1987;Tettelbach and Wenczel 1993). Recent work by Krause, however, showed about 25% of the scallops in the area were survivors of those released (Krause 1992). Subsequent reseeding efforts were further hampered by the presence of a shell-boring parasite, Po/ydora sp. and yet another "brown tide". While the enhancement efforts are encouraging, the status of the New York bay scallop fishery is still precarious.

Over 100,000 adult bay scallops were transplanted to western Bogue Sound, North Carolina in each of three successive years (1992, 1993, and 1994). Recruitment density at experimental sites increased by as much as 568% while adult densities after recruitment increased by as much as 258%. Recruitment appeared to limit population size in Bogue Sound which implied that larval subsidy through increased spawning stock may enhance bay scallops in the system (Peterson et al. 1996).

961

In 1996, the state of Florida began an enhancement program along the west coast of Florida from Tampa Bay to Crystal River. Scallops reared in a hatchery and nursery to about 20 mm in size were placed at selected locations in wire cages at a density of 300 per square meter. The growth and mortality of these were followed until spawning. Fouling and mortality of the scallops were severe in the late summer but spawning of the survivors is thought to have contributed to an increased population in the Crystal River area,

17.4 FUTURE

Bay scallops in the eastern United States have historically been considered a delicacy. especially in the local markets where the fresh product is consumed. Its high demand in these markets guarantees a continued high value. However, problems associated with the fishery will need to be addressed.

In addition to showing sharp natural seasonal and annual fluctuations in stock densities, bay scallops along the east coast of North America will continue to be influenced by other pressures that will limit harvests. Loss of habitat through the decline of seagrass beds and the degradation of habitat through algal blooms such as "brown tide" may contribute to the further decline of bay scallop stocks. Also the increase in the public awareness about the occurrence of "harmful algal blooms" may also lead to a decline in the consumption of bay scallops. These problems may eventually lead to the profitability of bay scallop aquaculture, especially if the whole-scallop market develops further. However, the success of bay scallop aquaculture will also be influenced by stringent, governmental leasing regulations, grow-out problems such as fouling, and market development.

The annual landings of the calico scallop fishery will probably continue at relatively low levels (7-10 million pounds) compared to 1984. Although the calico scallop has less value than the bay scallop, the continued landings will ensure its place in the scallop market. It is unlikely that demand for the product will lead to aquaculture ventures in North America.

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AUTHORS ADDRESSES

Norman J. Blake - College of Marine Science, University of South Florida, St. Petersburg, Florida 33701 USA (E-mail: nblake@marine.usf.edu)

Sandra E. Shumway - Dept of Marine Sciences, UCONN, 1080 Shennecossett Road, Groton, CT 06340 USA (E-mail: Sandra.Shumway@uconn.edu)

Developments in Aquaculture and Fisheries Science· 35

SCALLOPS: BIOLOGY, ECOLOGY AND AQUACULTURE

SECOND EDITION

Edited by

SANDRA E. SHUMWAY Department of Marine Sciences University of Connecticut Groton, Connecticut U.S.A.

G. JAY PARSONS Fisheries and Oceans Canada Aquaculture Science Branch Ottawa, Ontario Canada

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