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Status of Fishery Resources off the Northeastern US
NEFSC - Resource Evaluation and Assessment Division



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Revised
December 2006

Atlantic surfclam

Atlantic surfclam (Spisula solidissima)

by Larry Jacobson and James Weinberg






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Figure 34.1 Statistical areas used to define the Atlantic surfclam stock.
Figure 34.1 Statistical Areas Used

Distribution, Biology and Management

Atlantic surfclams, Spisula solidissima, are distributed along the western North Atlantic Ocean from the southern Gulf of St. Lawrence to Cape Hatteras (Figure 34.1). Commercial concentrations are found primarily off New Jersey, the Delmarva Peninsula, and on Georges Bank. In the Mid-Atlantic region, surfclams are found from the intertidal zone to a depth of about 60 m but densities are low at depths greater than 40 m. Surfclams occur in both state (≤ 3 mi from shore) and federal waters (i.e. the Exclusive Economic Zone or “EEZ”, between 3 and 200 mi from shore). The report deals only with the EEZ segment of the surfclam resource.

Maximum size is about 22.5 cm (8.9 in.) shell length, but surfclams larger than 20 cm (7.9 in.) are rare. Maximum age exceeds 30 years and surfclams 15-20 years of age are common in many areas.
Surfclams are capable of reproduction in their first year of life, although full maturity may not be reached until the second year. Eggs and sperm are shed directly into the water column. Recruitment to the bottom occurs after a planktonic larval period of about three weeks.

The Fishery

The fishery for Atlantic surfclams in the EEZ was among the first US fisheries managed using an individual transferable quota (ITQ) system. ITQ management was established in 1990 by the Mid-Atlantic Fishery Management Council under Amendment 8 to the Fishery Management Plan for the Atlantic Surfclam and Ocean Quahog Fisheries (FMP). Management measures include an annual quota for EEZ waters (which was 26.2 thousand metric tons meats per year during 2001-2005). Fisheries in state waters are managed by state authorities.

Surfclams recruit to the commercial fishery at 10-12 cm (4-5 in.) shell height and at about 5 years of age. Most of the surfclams landed in recent years were 8-12 years old.

Figure 34.2  Total commercial landings of surfclams from the EEZ, 1965-2005.
Figure 34.2

The principal fishing gear for surfclams is the hydraulic clam dredge. Recreational and foreign fishing are insignificant.

Surfclam landings from the EEZ averaged 17,000 metric tons per year during 1965-1983 and with a low of 6,400 metric tons in 1970 and a peak of 34,000 metric tons during 1974 (Table 34.1, Figure 34.2 [Fig 34.2 Data]). Landings during 1984-2005 averaged 22,000 metric tons per year. The Georges Bank region has been closed to the harvesting of surfclams since 1990, due to the risk of paralytic shellfish poison (PSP).

The fishery has seen considerable consolidation over the last few decades. During 1990, 128 vessels participated in the EEZ fishery for surfclams. The number of vessels in the fishery declined to 75 in 1991 with adoption of Amendment 8 and implementation of ITQ management. During 2005, only 50 vessels were active in the fishery.

Figure 34.3  Estimated fishable biomass and trends in NEFSC clam survey data for surfclams in the EEZ.  Survey data were rescalled to the same units as biomass.
Figure 34.3

Figure 34.4  Fishing mortality estimates for surfclams in the EEZ.
Figure 34.4

Research Vessel Survey Indices

The NEFSC clam survey is conducted once every three years and it is the main source of fishery independent trends in surfclam biomass. Trends in the survey are very similar to trends in estimated stock biomass (Figure 34.3 [Fig 34.3 Data]).

Assessment Results

The most recent stock assessment completed in 2006 indicates that total fishable biomass increased steadily from 1,020,000 metric tons in 1981 to a peak of 1,842,000 metric tons during 1997 (Figure 34.3 [Fig 34.3 Data]). After 1997, biomass declined steadily to 1,170,000 metric tons during 2005. Georges Bank is the region with the highest fishable biomass.

Fishing mortality estimates for the total stock peaked at 0.0266 during 1984 and then declined steadily to 0.0104 in 1998 (Figure 34.4 [Fig 34.4 Data]). After 1998, fishing mortality increased steadily and averaged about 0.0195 during 2004 and 2005.

Biological Reference Points

The biomass target (900,000 metric tons, a BMSY proxy) used by managers for the entire surfclam stock is one-half of the biomass during 1999. The biomass threshold (450,000 metric tons) is one-half of the target level. The fishing mortality threshold is equal to the assumed natural rate (0.15, an FMSY proxy). A fishing mortality target is not specified. (Table 34.2).

Summary

Atlantic surfclam biomass is moderately high and fishing mortality rates are relatively low. The stock was not overfished during 2005 because stock biomass (1,170,000 metric tons) exceeded the threshold level. As well, overfishing was not occurring during 2005 because the estimated fishing mortality rate (0.0192) was less than the threshold level. Southern areas have experienced declines in biomass during recent years due primarily to poor recruitment and slow growth rates associated with warm water conditions.

Old lineart drawing

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Table 34. 1 Quotas, landings data and estimates of biomass, fishing mortality and recruitment for EEZ Atlantic surfclams (thousand metric tons)..

  Category
1986-95
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
 
Average
                       
  Quota
23.0
19.8
19.8
19.8
19.8
19.8
22.0
24.2
25.1
26.2
26.2
  Landings
22.1
19.8
18.6
18.2
19.6
19.7
22.0
24.0
25.0
24.2
21.2
  Biomass
1,373
1,780
1,842
1,824
1,799
1,723
1,628
1,531
1,415
1,292
1,170
  Fishing Mortality
0.0179
0.0115
0.0105
0.0104
0.0114
0.012
0.0142
0.0166
0.0187
0.0199
0.0192
  Recruitment
153
185
189
116
121
76
62
63
43
32
27

 

Table 34.2 MSY Based Reference Points for Atlantic surfclams.

 MSY-based Reference Points
 Biomass threshold
= 450,000 metric tons
 Biomass target
= 900,000 metric tons
 Fishing mortality threshold
= 0.15
 Fishing mortality target
= Not specified

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For further information

L.M. Cargnelli, S.J. Griesbach, D.B. Packer, and E. Weissberger. 1999. Essential fish habitat source document: Atlantic surfclam, Spisula solidissima, life history and habitat characteristics. NOAA Technical Memorandum NMFS-NE-142. http://www.nefsc.noaa.gov/nefsc/publications/tm/tm142/

Collette, B.B. and G. Klein-MacPhee (eds.). 2002. Bigelow and Schroeder’s fishes of the Gulf of Maine. Smithsonian Institution Press, Washington, DC. http://www.gma.org/fogm/

Mid-Atlantic Fishery Management Council. 2005. Overview of the surfclam and ocean quahog fisheries and quota considerations for 2006 and 2007. Mid-Atlantic Fishery Management Council, Room 2115, Federal Building, 300 South New Street, Dover, DE 19904-6790.

NEFSC. 2007. 44th Northeast Regional Stock Assessment Workshop (44th SAW). 2007. 44th SAW Assessment Summary Report. NEFSC Ref. Doc. 07-03.

NEFSC. 2007. 44th Northeast Regional Stock Assessment Workshop (44th SAW). 2007. 44th SAW Assessment Report. NEFSC Ref Doc. 07-??.

Penttila, J. and L.M. Dery (eds.). 1988. Age determination methods for northwest Atlantic species. NOAA Technical Report NMFS 72. http://www.nefsc.noaa.gov/fbi/age-man.html

Weinberg, J.R., and T.E. Helser. 1996. Growth of the Atlantic surfclam, Spisula solidissima, from Georges Bank to the Delmarva peninsula, USA. Marine Biology 126: 663-674.

Weinberg, J.R. 1998. Density-dependent growth in the Atlantic surfclam, Spisula solidissima, off the coast of the Delmarva Peninsula, USA. Marine Biology 130:621-630.

Weinberg, J.R. 1999. Age-structure, recruitment, and adult mortality in populations of the Atlantic surfclam, Spisula solidissima, from 1978 to 1997. Marine Biology 134: 113-125.

Weinberg, J.R. 2005. Bathymetric shift in the distribution of Atlantic surfclams: response to warmer ocean temperature.

Northeast Fisheries Science Center (NEFSC). 2003. Atlantic surfclam. In: 37th Northeast Regional Stock Assessment Workshop (37th SAW) Stock Assessment Review Committee (SARC) Consensus Summary of Assessments. NEFSC Reference Document 03-16. http://www.nefsc.noaa.gov/nefsc/publications/crd/crd0316/

Weinberg, J.R., E.N. Powell, C. Pickett, V.A. Nordahl, Jr., and L. D. Jacobson. 2005. Results from the 2004 cooperative survey of Atlantic surfclams. Northeast Fisheries Science Center Reference Document 05-01. http://www.nefsc.noaa.gov/nefsc/publications/crd/crd0501/

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