Ocean Migration Rates of American Shad (Alosa sapidissima)

Abstract

Ocean migration rates of American shad (Alosa sapidissima), estimated from tag returns, averaged 21 km/day during the spring northward migration along the Atlantic coast between Chesapeake Bay and the Bay of Fundy and appear to be regulated by temperature preferences of the species. The fall southward migration is believed to occur at a similar rate. An evaluation of known saltwater swimming speeds and of prevailing currents along the migratory path indicates that the distance traveled during the northward and southward migrations may exceed the minimum distance route by up to 100 and 500%, respectively, and suggests that considerable nondirected movement may occur. The sustained swimming speeds of juvenile shad at the time of their entry into the sea are close to the estimated minimum sustained speeds required to complete the initial migration in the sea. Annual density-dependent variation in individual growth rate, through its influence on size at emigration and the resulting swimming performance of juveniles, may significantly influence juvenile survival. Key words: American shad, Alosa sapidissima, migration rates, swim speeds, survival