FISHHRV Hl'LI.ETIN V(1L 77. NO 1 



Figure 8. — Seasonal distribution of major American shad 

 catches in the International Commission for the Northwest At- 

 lantic Fisheries divisions. 1970-75, Cape Hatteras. N.C., toNova 

 Scotia. 



foreign midwater trawls or the wing trawl (Hol- 

 land**), but bottom trawl survey data provide the 

 most complete, available records on offshore oc- 

 currence. 



Based on the data presented, survey-related ob- 

 servations to be discussed, and literature to be 

 reviewed, we propose the following migratory 

 cycle for American shad. Offshore movements are 



'Holland. B. F., Jr. 1975 Anadromous fisheries research 

 program, northern coastal area. Section 11. N.C. Proj. AFCS 

 ll-lJob6, 43p 



limited to areas and depths with near-bottom 

 temperatures between 3° and 15°C. Shad occur 

 most frequently in offshore areas of intermediate 

 depths (appro.ximately 50-100 m). Adults that 

 survive spawning together with subadults mi- 

 grate to the Gulf of Maine or to an area south of 

 Nantucket Shoals and remain there through the 

 summer and early autumn. During this period of 

 active feeding, shad are vertical migrators and 

 follow the diel movements of zooplankton in the 

 water column. Most shad move out of the Gulf of 

 Maine in autumn with declining water tempera- 

 tures and congregate offshore, between southern 

 Long Island and Nantucket shoals (lat. .39"-4rN) 

 during the winter. Adults enter coastal waters in a 

 broad front toward the Middle Atlantic coast, as 

 far south as North Carolina during the winter and 

 spring. Shad populations returning to South At- 

 lantic rivers migrate south adjacent to the coast 

 and within the 15°C isotherm to reach home rivers 

 by winter and early spring. North Atlantic popu- 

 lations proceed north up the coast in the spring 

 with the warming of coastal waters above 3°C. 



Offshore Distribution 



The wide range of surface temperatures at sta- 

 tions where shad were caught does not support the 

 e.xtrapolation of the inshore temperatures-shad 

 migration regime proposed by Leggett and Whit- 

 ney (1972) to explain offshore movements. The 

 influence of temperature on fish behavior and 

 physiology is most pronounced during the spawn- 

 ing season (Laevastu and Hela 19701, particularly 

 for anadromous fishes. Tag returns within the 

 13°-18°C isotherms (Leggett and Whitney 1972) 

 may have reflected inshore physiological changes 

 in prespawning adults, leading to higher optimal 

 temperatures approaching those for spawning. 

 Our results indicate that near-bottom tempera- 

 tures between 3' and 15°C provide a better basis 

 for predicting shad movements in offshore waters. 



Offshore catches during NMFS surveys re- 

 vealed that shad are not limited to the Gulf of 

 Maine in summer months as reported by Talbot 

 and Sykes ( 1958). Shad were also collected in an 

 area south of Nantucket Shoals during summer 

 and autumn surveys. Although shad from most 

 river systems have been collected in the Gulf of 

 Maine during the summer (Talbot and Sykes 

 1958), it is not known whether all populations 

 migrate together at sea. Distribution during the 

 spring is widespread and not indicative of a syn- 



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