Cape Cod to Cape Hatteras, 4 included the Gulf of 

 Maine, and 7 included the region from Cape Hat- 

 teras to Cape Fear. During 1972-75, all inshore 

 surveys used either a % modified Yankee trawl or 

 the No. 36 Yankee trawl. Since 1976, a No. 41 

 Yankee trawl has been used. Towing procedures 

 were the same as described for offshore surveys. 

 The seasonal and geographic variation in the ex- 

 tent of inshore surveys reflects their evolution as 

 a monitoring tool. 



Capture data employed in this study included 

 date, location, time, depth, surface and bottom 

 temperatures, and number collected. Catch loca- 

 tions from all surveys were plotted to the nearest 

 10' of latitude and longitude on depth contour 

 maps by season. Surface and bottom tempera- 

 tures and depth frequencies were plotted for 

 each occasion that M. menidia were captured. 



Results 



Standard bottom trawl tows at 2,057 stations 

 from inshore surveys collected 979 M. menidia at 

 107 sites (5.2% occurrence), while offshore tows 

 at 10,209 stations captured 464 M. menidia at 72 

 sites (0.7% occurrence). Because sampling effort 

 by season was not uniform with respect to in- 

 shore and offshore surveys or geographic zones, 

 analysis of catch per effort data (catch fre- 

 quency) was compiled by month for inshore and 

 offshore surveys in three geographic regions 

 (i.e., Gulf of Maine-Georges Bank, Cape Cod- 

 Cape Hatteras, Cape Hatteras-Cape Fear). In 

 the inshore surveys, effort was primarily concen- 

 trated in the Cape Cod-Cape Hatteras region, 

 where the percent frequency of capture of M. 

 menidia was negligible in summer, increased in 

 November (4.9%), peaked in January (34.3%), 

 and declined through the spring (Table 1). Num- 

 ber of stations sampled in the inshore surveys of 

 the Gulf of Maine-Georges Bank and Cape Hat- 

 teras-Cape Fear regions was inadequate for 

 monthly or regional comparisons. In offshore 

 surveys, the monthly pattern of occurrence of M. 

 menidia was similar to that of inshore surveys; 

 catch frequency was zero in summer and 

 autumn, peaked in January (3.8%) in the Gulf of 

 Maine-Georges Bank and in February (11.2%) in 

 the Cape Cod-Cape Hatteras regions, and de- 

 clined thereafter (Table 2). These data support 

 the hypothesis of an offshore winter migration. 



The geographic distribution of catches by sea- 

 son (Fig. 1) indicates that most collections are 

 confined to a zone within roughly 50 km of the 



shoreline and within the 40 m depth contour. One 

 collection occurred 170 km from the mainland. 

 Although most catches appear to occur between 

 Cape Cod and Cape Hatteras and especially in 

 the New York Bight, sampling effort among in- 

 shore surveys was much greater in this region as 

 previously noted (Table 1). Although only four 

 collections of M. menidia were observed south of 

 Cape Hatteras (two off Cape Fear, S.C., and two 

 off Cape Romain, S.C.; not appearing in Figure 

 1), no offshore or inshore surveys were conducted 

 south of Cape Hatteras in winter when catches 

 might be expected. 



Surface temperatures recorded at 141 of the 

 inshore and offshore stations where Atlantic 

 silversides were captured ranged from l°to22°C, 

 but 86% of these were within a range of 2°-6°C (x 

 = 4.9°C; Fig. 2A). Bottom temperatures re- 

 corded at 135 collecting sites revealed a similar 



Table 1.— Percent frequency of occurrence of Men idia men id- 

 ia at stations sampled in the inshore survey region (depth 

 strata of 5-27 m) of the NMFS bottom trawl survey program 

 over the continental shelf of eastern North America. Catch sta- 

 tistics are from cruises conducted from 1972 to 1979 and are 

 pooled by month and area of capture. The number in paren- 

 theses is the total number of stations sampled. 



Table 2.— Percent frequency of occurrence of Men idia men id- 

 ia at stations sampled in the offshore survey region (depth 

 strata 27-366 m) of the NMFS bottom trawl survey program 

 over the continental shelf of eastern North America. Catch sta- 

 tistics are from cruises conducted from 1963 to 1979 and are 

 pooled by month and area of capture. The number in paren- 

 theses is the total number of stations sampled. 



Month 



Gulf of Maine and 

 Georges Bank 



Cape Cod- 

 Cape Hatteras 



Cape Hatteras- 

 Cape Fear 



146 



