LONG 

 ISLAND 



CHESAPEAKE 

 BAY 



GEORGES 

 BANK 



O 

 9 



. FALL 



* WINTER 



• SPRING 



O 50 IOO 



Km 



\CAPE 

 V1ATTERAS 



Figure 1. — Location of Atlantic silverside catches 

 by season during inshore and offshore bottom 

 trawl surveys of the National Marine Fisheries 

 Service, Cape Hatteras to Nova Scotia, 1963-79 

 (fall = Sept.-Nov.; winter = Dec.-Feb.; spring = 

 Mar.-May). Seven catch locations do not appear: 

 Two off the northern coast of Maine, one off the 

 outer coast of southern Nova Scotia, two off Cape 

 Fear, S.C., and two off Cape Romain, S.C. 



pattern: the majority (86%) of all Atlantic silver- 

 side collections occurred within a range of 2°-6° 

 C (x = 5.1°C; Fig. 2B). These data indicate that 

 M. menidia occur over the continental shelf pri- 

 marily under winter temperature conditions 

 after fall overturn when temperatures are iso- 

 thermal. 



The distribution of Atlantic silversides with 

 respect to depth was examined by comparing 

 catch frequency to depth of capture in 5 m inter- 

 vals. The majority of catches occurred in waters 

 <50 m deep (86%), and 42% of all catches were in 

 depths of 10-20 m (Fig. 3). Maximum depth of 

 capture was 126 m. 



Some aspects of the winter ecology of Atlantic 

 silversides while at sea can be revealed by exam- 

 ining their vertical distribution in the water 

 column. Vertical distribution was inferred from 



diel variations in capture times partitioned in- 

 to six 4-h intervals. Chi-square analysis com- 

 paring catch frequency in each time interval to 

 all others combined showed that catch frequen- 

 cies during night intervals (2000-0359 h) were 

 significantly less than expected (P<0.01; Table 

 3), while catch frequencies during midday inter- 

 vals (0800-1559 h) were significantly greater 

 than expected (P<0.01). Apparently, M. menidia 

 occurred nearer the bottom during daylight 

 hours and hence were more susceptible to bot- 

 tom trawl tows conducted during the day. These 

 observations indicate that while at sea, Atlan- 

 tic silversides are vertical migrators like 

 other planktivores such as Atlantic herring, 

 Ciupea harengus, (Blaxter 1975) and American 

 shad, Alosa sapidissima, (Neves and Depres 

 1979). 



147 



