WATER TEMPERATURE AND THE MIGRATIONS OF AMERICAN SHAD 



William C. Leggett' and Richard R. Whitney' 



ABSTRACT 



The peak of spawning runs of American shad (Alosa sapidissima) into rivers at various 

 latitudes on the Atlantic and Pacific coasts of North America takes place when water 

 temperatures are near 18.5 °C. At the Bonneville Dam, Columbia River, Wash., 90% of 

 the run as a rule takes place when river temperatures are between 16.0° and 19.5°C. 

 At the fish ladder of the Holyoke Water Power Company on the Connecticut River, the 

 temperature at the peak of the shad run averaged 19.5°C for 15 years. In the St. Johns 

 River, Fla., peak movement occurs in December and January at the time of the annual 

 minimum water temperatures, or 14.0° to 20.0°C. 



Migrations of shad in the Atlantic Ocean follow paths associated with approximately 

 the same range of temperatures (13.0°-18.0°C). Annual cycles of ocean warming cause 

 shad to move into the Gulf of Maine in the summer, to the middle Atlantic in the winter, 

 and to the south in the early spring. Juvenile shad move downstream in the fall, coin- 

 ciding with a decline in the temperature of each stream to below 15.5°C. A path of 

 migration for shad in the Pacific Ocean is hypothesized from the known seasonal changes 

 in ocean temperature. The potential effects of artificial warming of streams on timing 

 and survival of shad runs in northern and southern latitudes is discussed. 



The American shad (Alosa sapidissima), in 

 spite of declines in abundance on the Atlantic 

 coast of the United States caused by obstruction 

 of spawning runs by dams, by water pollution, 

 and by overfishing, continues to provide a catch 

 each year of some 8 million pounds valued at 

 slightly more than one million dollars to the fish- 

 ermen (Walburg and Nichols, 1967). 



There is as yet no rationally based manage- 

 ment scheme to prevent overfishing of shad, and 

 dams and pollution continue to increase. Recent 

 changes in the environment for shad have been 

 brought about by the greatly increased heating 

 of the water by steam-electric generating sta- 

 tions. There will be a further increase in the 

 construction of these facilities; thus the Federal 

 Power Commission in 1960 estimated that by 

 1980 the generating capacity of hydroelectric 

 power stations would double — some accom- 

 plished by construction of dams and some by ad- 

 ding capacity at existing dams — but at the same 

 time, steam-electric capacity would triple (Fed- 

 eral Power Commission, 1960). Other experts 



^ Essex Marine Laboratory, Essex, Conn.; present 

 address: Department of Biology, McGill University, 

 Montreal 101, Quebec, Canada. 



' Washington Cooperative Fishery Unit, College of 

 Fisheries, University of Washington, Seattle, WA 98195. 



regard these estimates as conservative (Amer- 

 ican Public Power Association, 1960). It there- 

 fore becomes pertinent to ask what effects the 

 warming of water may have on fish in streams 

 used for cooling. This paper analyzes the eflfect 

 of water temperature on the movements of shad 

 in streams and in the ocean. 



It is appropriate that this paper, which traces 

 the relationship of migrations of American shad 

 to temperature of the water, should appear in a 

 volume dedicated to Dr. 0. Elton Sette. His in- 

 terest in the eflfects of temperature on migrations 

 of fishes has been a stimulus to the work of his 

 colleagues for over 30 years. He has always been 

 generous in his encouragement of those around 

 him. In 1957, the Pacific Oceanic Fishery In- 

 vestigations, of which he was the first Director, 

 began publication of monthly sea-surface tem- 

 perature charts for the Pacific Ocean as an aid to 

 fishermen and biologists studying fish distribu- 

 tion. The successors of these charts are still be- 

 ing issued by the National Marine Fisheries Ser- 

 vice, Southwest Fisheries Center, La Jolla 

 Laboratory. Other scientists and agencies have 

 come to see their utility and popularity and have 

 commenced publication of sea surface temper- 

 ature charts for other parts of the world. 



Manuscript accepted March 1972. 



FISHERY BULLETIN: VOL. 70, NO. 3, 1972 



659 



