THE OCEANIC MIGRATION OF AMERICAN SHAD, 

 ALOSA SAPIDISSIMA, ALONG THE ATLANTIC COAST 



Richard J. Neves' and Linda Depres^ 



ABSTRACT 



The migratory route of American shad. A/osa sapidissima. in the Atlantic Ocean was studied using 14 

 yr of catch data collected during bottom trawl surveys by the U.S. National Marine Fisheries Service 

 (and its predecessorl and cooperating foreign countries. All shad catches occurred at bottom tempera- 

 tures from 3° to 15°C. with the most frequent catches between 7° and 13°C. Water temperatures 

 between initial and peak entry of shad into home estuaries along the Atlantic coast are within the same 

 thermal regime (3^-15^C). During the summer, ail shad catches occurred north of lat. 40^N in two 

 primary areas; Gulf of Maine and an area south of Nantucket Shoals. Previous studies on food habits 

 and differences in time of capture during National Marine Fisheries Service surveys indicated that 

 shad were vertical migrators, probably following the diel movements of large zooplankters in the water 

 column. Shad were generally absent from the Gulf of Maine by late autumn, and concentrations were 

 found between lat. 39° and 4 1 °N during the winter. Based on previous tagging studies. National Marine 

 Fisheries Service surveys, and coastal temperature data, most prespawning adults enter coastal 

 waters along the Middle Atlantic Bight from lat. 36' to 40°N and then proceed north or south to natal 

 rivers. Coastal surveys for river herring by North Carolina's anadromous fishery research program and 

 commercial shad catches re[)orted to the International Commission for the Northwest Atlantic 

 Fisheries by member nations concur with our proposed bottom temperature (3°-15^^C)-migratory route 

 hypothesis for shad. 



The American shad, Alosa sapidissima, is an 

 anadromous fish ranging from the St. Johns River, 

 Fla., to the St. Lawrence River, Canada i Walburg 

 and Nichols 1967). Meristic and tagging studies 

 indicate that discrete spawning populations of 

 shad exist in river systems along the Atlantic 

 coast (Mollis 1948; Hill 1959; Nichols 1960. 1966; 

 Carscadden and Leggett 1975a). Juveniles leave 

 freshwater in autumn and generally remain in the 

 ocean for 3-5 yr before returning to their natal 

 rivers to spawn. Spawning runs occur in a south to 

 north temporal progression, beginning as early as 

 December in Florida and as late as June in Canada 

 (Walburg 1960). Virtually all shad south of Cape 

 Hatteras, N.C., die after spawning, whereas the 

 percentage of repeat spawners in rivers north of 

 North Carolina increases with latitude I Leggett 

 1969; Chittenden 1975). 



A considerable amount of literature exists on 

 this species because of its commercial and recre- 

 ational importance inshore, but little research has 



'Massachusetts Cooperative Fishery Research Unit, Depart- 

 ment of Forestry and Wildlife Management, University of Mas- 

 sachusetts, Amherst, Mass.; present address; Virginia Coopera- 

 tive Fishery Research Unit, Virginia Polytechnic Institute & 

 State University, Blacksburg, VA 24061. " 



^Northeast Fisheries Center Woods Hole Laboratory, Na- 

 tional Marine Fisheries Service. NOAA, Woods Hole, MA 02543. 



Manuscript accepted .August 1978. 

 FISHERY BULLETIN VOL. 77. NO 1.1979 



been done on the oceanic phase of its life history. 

 Talbot and Sykes (1958) provided the first evi- 

 dence of an annual oceanic migration based on 19 

 yr of tagging studies by the U.S. Fish and Wildlife 

 Service. Tag returns indicated that shad from U.S. 

 rivers congregated with those from Canadian riv- 

 ers (Vladykov 1950. 1956) in the Gulf of Maine 

 during summer and autumn and moved south to 

 possibly overwinter off the Middle and South At- 

 lantic States (Talbot and Sykes 1958; Walburg 

 1960; Walburg and Nichols 1967; Cheek 1968). In 

 the spring, shad moved north or south toward 

 natal rivers to spawn. 



Temperature monitoring in rivers with major 

 shad runs, and laboratory experiments, have pro- 

 vided convincing evidence that the timing of diad- 

 romous movements corresponds with specific 

 water temperatures (Walburg and Nichols 1967; 

 Chittenden 1969, 1972; Williams and Bruger 

 1972; Leggett and Whitney 1972; Leggett 1973). 

 Leggett and Whitney (1972) also postulated that 

 the oceanic distribution of shad was temperature- 

 controlled; tag returns plotted on surface isotherm 

 charts fell within the 13°-18°C isotherms. How- 

 ever, all of the tag returns used to establish this 

 "migrational corridor" at sea were collected in- 

 shore during the spring coastal migration toward 



199 



