NO A A PROFESSIONAL PAPER 11 



stations were about 9.3 km apart. Stations at depths of 22 

 to 59 m and 2 to 56 km from shore were sampled. The 

 survey did not cover the entire Middle Atlantic Bight scal- 

 lop resource, because the weather was inclement, but sub- 

 stantial numbers of scallops had been killed by the anoxic 

 conditions. During November 8-17, the entire New Jersey 

 scallop resource was surveyed. A total of 45 stations about 

 9.3 km apart and 13 to 70 km from shore were sampled. 

 The scallop mortality was somewhere between 8.8 to 12.9 

 percent. ^ 



Assessment cruises were made south of Long Island 

 before, during, and after the oxygen-depletion event. No 

 abnormal clam, quahog, and scallop mortalities were ob- 

 served (Northeast Fisheries Center 1977a). 



Post-Anoxia Surveys 



During the January 26 to March 17, 1977, resource as- 

 sessment survey, 224 stations were sampled in the Middle 

 Atlantic Bight and southern New England area (Northeast 

 Fisheries Center 1977b). In the New Jersey area, 70 sta- 

 tions were sampled at depths of 9.1 to 82.3 m in and 

 beyond the area affected by the 1976 anoxic conditiiins. 

 Some evidence of mortality may have been lost in the 

 period after the October 1976 sampling and the 1977 sur- 

 vey, because paired valves had separated. An analysis 

 comparing the results of the April-May 1976 and 1977 

 assessment cruises, however, clearly showed that the high- 

 est mortality of surf clams and ocean quahogs was off New 

 Jersey (table 11.1-2). Some 20.7 percent of the surf clams 

 and 26.6 percent of the ocean quahogs were dead off New 

 Jersey in 1977, compared with 5.0 percent and 3.9 percent 

 in 1976. For the Long Island area in 1977, mortalities of 

 the clam and quahog were both <3.5 percent,for the Dcl- 

 marva area, both <8.3 percent. Surveys since 1970 did 

 not include the southern New England area. 



The surf clam impact or mortality area (fig. 1 1.1-1), as 

 defined from assessment cruises and fishermen's reports, 

 extended from immediately north of Manasquan Inlet 

 (40° lO'N), southward to immediately south of Atlantic 

 City (39° lO'N), and offshore to about 37 m depth (North- 

 east Fisheries Center 1977b). Mortalities were noted in 

 inshore areas (3-5 km from the beach), but the effects of 

 the mortality were sporadic and less severe than offshore 

 (Milstein et al. 1977; Northeast Fisheries Center 1977b; 

 Schneider et al. 1977). Ocean quahog mortalities were 

 noted within the same latitudinal boundaries (fig. 11.1-1) 

 from 18 to 55 m depth (Northeast Fisheries Center 1977b). 

 Figure 11.1-2 shows two areas of the continental shelf off 

 New Jersey with live (unaffected) and dead or stressed 

 (affected) sea scallops. Affected scallops were at the 

 shoreward edge of the scallop distribution and along about 

 60 percent of its north to south length. Apparently all 

 scallops were dead within the affected area. The areas of 

 maximum mortality were 6,750 km- for surf clams, 9,105 

 km^ for ocean quahogs, and 4,300 km' for sea scallops. 



Analysis of Catch-Per-Tow 



Catch-per-tow data from the April-May 1976 (North- 

 east Fisheries Center 1976a) and January-March 1977 

 (Northeast Fisheries Center 1977b) assessment cruises off 

 the New Jersey coast were stratified by areas correspond- 

 ing with the impact area and depth distribution of each 

 species. Three strata were defined for surf clams: 1 ) within 

 the impact area (£37 m), 2) north and south of the impact 

 area {^31 m), and 3) east of the impact area (>37 - 

 <55 m). Ocean quahog data were also grouped into three 

 strata: 1) within the impact area (>18 - <55 m), 2) north 

 and south of the impact area (>18 - <55 m). and 3) east 

 of the impact area (>55 m). 



For an initial comparison of the data from the surveys, 

 the catches in each stratum were reduced to the mean 

 number per tow, standard deviation, and standard error. 

 Confidence intervals of 95 percent were calculated for the 

 means. 



The mean meat weight of individuals caught in a par- 

 ticular stratum and year was computed for each species 

 by the following methods. The shell length composition 

 from each station in the stratum was determined by pro- 

 rating the total catch by the measured subsample. The 

 cumulative stratum length frequency was then calculated 

 by summing the catches from each station. Weights for 

 each millimeter length interval were calculated from the 

 appropriate length/weight relation for each species (Ropes 

 1971; unpublished Northeast Fisheries Center data). The 

 overall stratum mean weight was derived by multiplying 

 the weight at each millimeter interval by the correspond- 

 ing frequency, summing over all intervals, and then di- 

 viding by the total number caught in the stratum. 



Table 11.1-3 summarizes catch data and associated sta- 

 tistics for surf clams. Numbers per tow within the mortality 

 area declined by 81.3 percent from 1976 to 1977; mean 

 weight per tow decreased 86.5 percent. Al stations outside 

 the mortality area (^37 m), catch per tow decreased 37.1 

 percent, average weight decreased 57.9 percent because 

 the mean weight of clams measured also declined. Few 

 clams were collected in the >37 to < 55 m zone, and num- 

 ber per tow decreased by only 71.1 percent. The results 

 of statistical tests suggest a significant (P <0.01) decline 

 in the impact areas. All other comparisons were nonsig- 

 nificant at the 0.05 level. 



Within the impact area, mean catch of ocean quahogs 

 per tow decreased 26.6 percent and mean weights 25.6 

 percent (table 11.1^). East of the mortality area, at 

 depths of >18 to <55 m, average numbers and weights 

 increased 10.1 percent and 26.9 percent, respectively. At 

 depths >55 m, average numbers and weights decreased 

 52.2 percent and 58.0 percent, respectively. Although 

 mean numbers per tow decreased at depths >55 m, the 

 difference was not significant, because one exceptionally 

 large catch in 1976 (958 individuals) again increased the 

 mean and variance for that year. Differences in catches 



266 



