NEVES and DESPRES: OCEANIC MIGRATION OF AMERICAN SHAD 



the U.S.S.R., Poland, and France from 1969 to 

 1976, mainly between Georges Bank and Cape 

 Hatteras. Spring trawl surveys, intended primar- 

 ily as juvenile herring surveys, have been made 

 since 1973 by vessels from U.S.S.R., Poland. Ger- 

 man Democratic Republic, and Federal Republic 

 of Germany between Nova Scotia and Cape Hat- 

 teras. Most of the foreign surveys followed NMFS 

 sampling procedures, sampled all or selected 

 strata wiihin respective survey areas, but used 

 various types of bottom trawls. All spring and 

 autumn surveys and additional cruises during 

 summer and winter are summarized in Table 1. 

 Survey station and catch data pertinent to this 

 study included: date, location, time, depth, bottom 

 and surface temperatures, and number, length 

 frequencies, and weight of shad caught. 



We plotted catch locations from all surveys (Ta- 

 ble 1) by 10' rectangles of latitude and longitude 

 on depth contour maps according to month or sea- 

 son. Locations of shad collections during spring 

 (March-May) and autumn (September-November) 

 were plotted by month. Summer (June-August) 

 and winter (December-February) surveys were 

 grouped by season because of less sampling effort 

 and lower catch frequency. Commercial shad 

 catches by month reported to the International 

 Commission for the Northwest Atlantic Fisheries 

 (ICNAF) by member nations from 1970 to 1975 

 were provided by Hodder'" and used to define major 

 shad catches within each ICNAF division and 

 their correlation with distribution patterns based 

 on survey data. Surface and bottom temperatures 

 (nearest 1°C) were plotted for each trawl tow that 

 collected shad; foreign catches with missing tem- 

 perature data were omitted from this analysis. 

 Additional oceanographic data on temperature 

 ( Walford and Wicklund 1968; Colton and Stoddard 

 1972; Churgin and Halminski 1974; U.S. Coast 

 Guard Oceanographic Unit^) and oceanic currents 

 (Bumpus and Lauzier 1965; Stommel 1965; Bum- 

 pus 1973) were reviewed for seasonal patterns 

 along the Atlantic coast. 



RESULTS 



Bottom trawls at 10,435 stations during the 77 



Table l, — Summary of bottom trawl surveys conducted by 

 United States and foreign research vessels between Cape Hat- 

 teras, N.C, and Nova Scotia, 1963-76, 



=V. M. Hodder. ICNAF Office. Dartmouth. N. S., Canada B2Y 

 3Y9. pers. commun. July 1977. 



■^U.S. Coast Guard Oceanographic Unit. 1970, 1975. 

 Monthly temperature charts. January to December 1970. 

 January to December 1975. available US Coast Guard 

 Oceanographic Unit. Bldg 159-E Navy Yard Annex. 

 Washington, DC 20590 



surveys collected 4,770 subadult and adult shad at 

 527 stations throughout the survey area. United 

 States and foreign research vessels accounted for 

 315 and 212 of the successful collecting stations, 

 respectively. Shad ranged in size from 8 to 50 cm 

 fork length (FL). Surface and bottom tempera- 

 tures were recorded at 448 of these stations and 

 used to plot catch frequency at 1°C intervals. Shad 

 were collected at survey stations with surface 

 temperatures between 2° and 23°C, and frequent 

 catches occurred throughout most of this temper- 

 ature range (Figure 2). Bottom temperatures at 

 successful collecting stations ranged from 3° to 

 15°C, but primarily between 5° and IS'C (Figure 

 3). Most stations with bottom temperatures <3°C 

 occurred in the Gulf of Maine during late winter 

 and early spring; stations with bottom tempera- 

 tures >15°C were mainly off the mid-Atlantic 

 coast during late summer and early autumn. This 

 apparent relationship between shad occurrence 

 and bottom temperatures was examined further 

 by comparing the catches of shad with total sam- 

 pling effort at each temperature (Table 2). Bottom 

 temperatures during surveys ranged from 1° to 

 23°C, but shad were captured only between 3° and 

 15°C. Shad catches occurred more frequently at 



li 



Flcl'RE 2 — Surface temperatures at 448 stations where Ameri- 

 can shad were collected during bottom trawl surveys, 1963-76, 

 Cape Hatteras, N.C, to Nova Scotia. 



201 



