CHAPTER //, PART 1 



TabI-E 1 1 . 1-2. — Live and dead surf clams and ocean quahogs. NMFS l'J76 and 1977 assessment cruises 



Surf clams 



Area 



Live 



Dead 



Percent 

 dead' 



Ocean quahogs 



Live 



Dead 



Percent 

 dead' 



1976 



Long Island 

 New Jersey 

 Delmarva Peninsula 

 Total 



1977 



Long Island 

 New Jersey 

 Delmarva Peninsula 

 Total 



Paired valves. 



per tow outside the kill area (>18 - <55 m) were also 

 insignificant. 



The sea scallop has substantially higher density on the 

 offshore than the inshore part of its distribution off New 

 Jersey. The average number of scallops per station, as 

 determined by the 1975 survey and the November 8-17, 

 1976. survey, were 6.2 and 4.0 times larger, respectively, 

 in the unaffected than in the affected areas. The mortality 

 of the total New Jersey scallop resource was between 8.8 

 and 12.9 percent. 



Estimates of Population Loss 



A measure of the New Jersey surf clam and ocean 

 quahog populations was calculated from the 1976 and 1977 

 assessment data, using the catch-per-tow data. The min- 

 imum number of clams and quahogs in each stratum was 

 computed by obtaining the possible number of sampling 

 units in a stratum area, based on the average area swept 

 by the dredge and multiplying the resultant weighting fac- 

 tor by the mean catch (in numbers) per tow. The standing 

 stock in meat weight was determined by multiplying the 

 number by the average meat weight of each clam. 



Tables 11.1-5 and 11.1-6 show biomass data of surf 

 clams and ocean quahogs computed from areal expansions 

 of mean catch-per-tow data. The calculations are minimal 

 estimates of population sizes, because the hydraulic 

 dredge is not 100 percent efficient in sampling (Northeast 

 Fisheries Center 1977b). 



The biomass of all New Jersey surf clams decreased 78.5 

 percent from 1976 to 1977. Within the mortality area, the 

 estimated decrease in meat weight of surf clams was 

 147,000 metric tons (t), or 62.6 percent of the total New 

 Jersey biomass of surf clams. Removal of clams by fishing 

 accounted for a very small proportion of the biomass de- 

 cline in the mortality zone. From May to December 1976 

 (after the 1976 survey, before the 1977 cruise) landings 

 at Pt. Pleasant and Atlantic City were 2,376 t. If the quan- 



tities are subtracted from the total, about 62 percent of 

 the biomass of New Jersey surf clams and 85 percent of 

 the biomass within the mortality area was lost. 



Effects of oxygen depletion on ocean quahog popula- 

 tions were much smaller because the largest concentra- 

 tions of quahogs off New Jersey were east of the mortality 

 area. The biomass of New Jersey quahogs declined 7.1 

 percent from 1976 to 1977; however, we know that vessels 

 from Pt. Pleasant and Atlantic City began removing some 

 of the quahogs in 1976. If the quantities are subtracted 

 from the losses, the anoxic conditions killed 25.4 percent 

 of the biomass within the mortality area and 6.3 percent 

 of the New Jersey total. 



Data were not available to estimate the loss of sea scal- 

 lop biomass. 



EFFECTS ON COMMERCIAL LANDINGS 



Surf Clam 



The effects of clam mortality were reflected in areas 

 where clammers fished and lower landings of surf clams 

 at New Jersey ports. In the first 4 months of 1976, vessels 

 from Atlantic City, Cape May-Wildwood, and Pt. Pleasant 

 concentrated fishing on dense beds of small clams near 

 shore; landings at Atlantic City were particularly high (fig. 

 11.1-3). After May 1, 1976, landings decreased as the 

 vessels moved offshore to comply with State of New Jersey 

 regulations that limited fishing on the inshore clams. Al- 

 though landings in July increased over those in June for 

 all ports, fishermen from Pt. Pleasant and Atlantic City 

 found dead and dying clams in their catch by mid- to late 

 July. Thereafter, landings declined substantially. At Pt. 

 Pleasant in August, landings were 57.1 t, as compared 

 with 120.4 t landed in July, a drop of 52.8 percent; at 

 Atlantic City in August landings were 184.8 1, as compared 

 with 613.8 percent in July, a drop of 69.9 percent. Land- 



267 



