Shad don't acclimate well with rapid water temperature changes this time of year, die offs are pretty common.
http://www.dec.ny.gov/press/90216.html"Mortality of gizzard shad in late winter and early spring is common and occurs cyclically, although it usually affects lower numbers of shad locally," said Regional Fisheries Manager Mike Clancy. "This species is very sensitive to cold water temperatures and their inability to acclimate causes mortality at low temperatures."
If you’ve seen a lot of small dead fish floating on your reservoir this winter, don’t be alarmed. They are most likely threadfin or gizzard shad, and they are easily killed by cold water temperatures and rapidly changing weather.
Shad are very sensitive to temperature and do not feed or move around much when temperatures fall below 50 degrees Fahrenheit. Die-offs typically occur when water temperatures drop to between 40-55 degrees, particularly when the change in temperature is quick and drastic. An arctic front with high winds may cool a shallow body of water by five degrees or more, increasing the potential for shad die-offs.
Die-offs also can occur in the spring when warm winds cause water temperatures to climb too quickly for shad to become acclimated.
