years later (1983-84) the 5-mean catch was one 

 of the highest recorded. The 1986-87 catches 

 were low at both stations but will probably re- 

 bound when conditions are better suited for re- 

 productive success. 



Silversides 



Two species of silversides dominate the shore 

 zone along the Connecticut coast, the Atlantic 

 silverside and the inland silverside. Both species 

 are sympatric along the Atlantic coast, wdth the 

 Atlantic silverside ranging from the Gulf of St. 

 Lawrence to the Chesapeake Bay and the inland 

 silverside ranging from Cape Cod to South Car- 

 olina (Johnson 1975). Both species spawn as 

 yearlings and have a life cycle that ranges from 1 

 to 2 years. Both are omnivorous, feeding on 

 copepods, mysid shrimp, fish eggs, and young 

 squid. They are important as forage food for 

 larger fish species (Bigelow and Schroeder 1953). 



Silversides collected in MNPS programs were 

 not always identified to species. When identified, 

 the Atlantic silverside was the most abundant 

 (over 90%). However, to determine long-term 

 trends the two species were analyzed as a single 

 taxon. Silversides dominated seine collections, 

 accounting for over 80% of the total catch (Ap- 

 pendix IV). They were also among the top-ranked 

 taxa collected in the trawl and impingement pro- 

 grams (Tables 1 and 4). Silversides were not 

 abundant in plankton samples because their eggs 

 are adhesive (Bigelow and Schroeder 1953) and 

 larvae and juvemles stay close to shore (Bayliff 

 1950). 



Seasonal patterns of abundance occurred in the 

 seine, trawl, and impingement collections. They 

 were found in seine collections in the spring, sum- 

 mer, and fall and in trawl and impingement col- 

 lections during the winter. This pattern suggested 

 that silversides in the MNPS area overwintered 

 in waters close to shore. Offshore winter migra- 

 tions of silversides have been reported in other 

 studies (BayliPf 1950; Bigelow and Schroeder 1953; 

 Conover 1979; Conover and Murawski 1982). 

 Conover (1979) found that silversides in Massa- 



chusetts migrated about 50 km offshore in winter 

 to depths of 100 m and only 1% of the population 

 returned inshore the following spring. In the 

 MNPS area, the rate of return (mean number per 

 haul in the fall compared to the spring) was cal- 

 culated starting in 1984, the first year sampling 

 was done at least once a month and biweekly 

 from April through October. The average return 

 rate at the three stations ranged from about 9% 

 in 1985 to about 40% in 1986. Silversides in LIS 

 may have a different overwintering strategy than 

 fish that overwinter in the Gulf of Maine. Winter 

 water temperatures in LIS do not approach the 

 rC lethal limit for silversides (Hoff aind Westman 

 1966), but average 2.5-4°C. Thus, silversides in 

 LIS may not have to move as far offshore to find 

 tolerable winter water temperatures. 



Because of the additional thermal effluent in 

 Jordan Cove, a potential exists for changes in the 

 distribution of silversides inhabiting the shore- 

 zone at JC and WP. Sampling at these two sites 

 and at control station GN was doubled in 1984 

 from monthly to biweekly (April through Octo- 

 ber) to increase our ability to detect any changes. 

 Annual 5-mean catches were calculated for each 

 of the three seine sites (Table 14). The 1986 



TABLE 14. Seasonal 5-mean catch (CPUE) and 95% 

 confidence interval of silversides by seine. 



1976" 



1977 1251 ± 2094 151 ± 569 62 ± 168 



1978 26 ±20 32 ± 64 24 ± 35 



1979 41 ±55 26 ± 27 15 ± 12 



1980 479 ± 930 104 ±96 55 ± 70 



1981 114 ± 107 81 ±72 31 ± 40 



1982 108 ± 102 48 ± 112 192 ± 567 



1983 580 ± 989 42 ± 59 112 ±158 



1984 35 ± 35 11 ± 9 3 ± 1 



1985 23 ± 14 18 ± 11 6 ± 4 



1986 200 ± 404 58 ±48 16 ± 10 



Season used for calculating 5-mean was June-November 

 at all stations 

 Not enough data available in 1976 to calculate 5-mean 



Fish Ecology Studies 275 



