Some interesting information on shad kills:

The most critical need of threadfin shad is stable temperature. They cannot stand drastic temperature changes. The lowest temperature threadfin can survive is 40 F and then only for a short time. If the water were colder than 40 F for more than 2 days all threadfin shad would die. Threadfin start to shiver when temperatures fall to 57 F. Shad behavior between 57 and 40 F is important for winter angling. Generally, water cools slowly . In these conditions shad seek out the warmest water available. Shad dive to deep water where water temperature is constant. Shad do not feed or move much when temperatures is below 50 F since they are totally driven by temperature and staying alive. They can acclimate to cold water but they don’t have to like it. Shad are schooling fish and cold temperatures make them school more tightly and in larger numbers. Storms with high winds are a shad’s worst nightmare. Rapid temperature change is lethal in the 40-55 F zone. Death comes just as certain to shad in the spring when a warm wind can warm the water too quickly for shad acclimated to cold water. That is why shad go deep to find stable temperature that cannot be as readily influenced by surface winds.