FISHERY BULLETIN VOL 77. NO 1 



home rivers. The correlation between offshore dis- 

 tribution and surface temperatures was therefore 

 based on extrapolation. 



The U.S. shad fishery is essentially an inshore 

 operation and commercial catch records have lim- 

 ited value in evaluating the distribution of shad at 



CAPE 

 HATTERAS 



sea. Previous tagging studies have relied on other 

 commercial fisheries for offshore tag returns, but 

 these fisheries concentrate effort at a time or place 

 where principal species aggregate. Tag returns 

 from shad taken as bycatch may therefore contain 

 a geographical bias and reflect only the distribu- 

 tion of fishing effort. This paper examines offshore 

 collections of shad from 14 yr of bottom trawl sur- 

 veys by United States and foreign research vessels 

 and interprets available literature on the coastal 

 occurrence of shad. An alternative temperature- 

 based hypothesis is presented to explain the 

 offshore migratory cycle of shad. 



METHODS 



The U.S. National Marine Fisheries Service 

 (NMFSi and its predecessor have conducted au- 

 tumn bottom trawl surveys since 1963 using the 

 RV Albatross IV and the RV Delaware II. The 

 survey area extends from Nova Scotia to Cape 

 Hatteras, out to 366 m (200 fm) (Figure 1) and is 

 stratified into geographical zones based on depth 

 and area. Coastal sampling stations are outside 

 the 27-m (15-fm) depth contour. Middle Atlantic 

 stations between New Jersey and Cape Hatteras 

 were added during autumn 1967. A stratified ran- 

 dom sampling design is used in the surveys; trawl 

 stations are allocated to strata in proportion to 

 stratum area and randomly assigned within 

 strata (Grosslein 1969). A standard No. 36 Yankee 

 bottom trawl with a 1.25 cm stretched mesh cod 

 end liner is towed at each station for 30 min at an 

 average speed of 3.5 kn. Autumn surveys were 

 conducted 24 h/day during 1963-76, between 3 

 September and 16 December. 



Spring bottom trawl surveys have been con- 

 ducted by NMFS since 1968 over the same geo- 

 graphical area (Figure 1). The No. 36 Yankee 

 trawl was used from 1968 to 1972 and a larger No. 

 41 Yankee trawl from 1973 to 1976. Trawling pro- 

 cedures were the same as during autumn surveys 

 and occurred between 4 March and 16 May. A 

 detailed description of NMFS bottom trawl sur- 

 veys and survey procedures is provided by 

 Flescher-' and Grosslein.'' 



In addition to U.S. cruises, periodic autumn 

 trawl surveys were conducted cooperatively with 



Figure L— National Marine Fisheries Service bottom trawl 

 surve.v area between 27 and 366 m. Cape Hatteras. N.C.. to Nova 

 Scotia, western North Atlantic. 



^Flescher, D. 1976. Research vessel cruises. 1963-1975 

 National Marine Fisheries Service Woods Hole, Massachusetts. 

 NMFS, Woods Hole, Mass., Lab. Ref. No. 76-14, 30 p. 



"Grosslein, M, D, 1969. Groundfish survev methods. 

 NMFS, Woods Hole, Mass., Lab. Ref. No. 69-2, 34 p. 



200 



