Some migrate up to 3000 km during Spring and Fall migration. They return to natal river to spawn. American Shad is intolerant of cold water temperatures. It requires well oxygenated waters either in river or in sea. Larvae intolerant of full strength ocean water.
Many eggs fail to fertilize and only a small percentage hatch.
High egg mortality has been attributed to failure to fertilize, suffocation, fungus infection and predation. Date 26 AUG 96 sharks, bluefish tuna, Kingfish and porpoises. Adults have few enemies except for humans. Spawning runs may begin as early as February, but are most frequent in April. Successful hatches have been reported at salinities ranging from 7.5 ppt at 12.0 oC to 15 ppt at 17 oC. No eggs hatched at a salinity of 22.5 ppt.