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Shad die-off is normal in winter

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.

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Gizzard shad

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Threadfin shad

Shad are soft, elongated fish without sharp spines, distinguished by the long threadlike last dorsal fin ray on their backs. Both species have a bluish gray back and a greenish or silver tinge overall. The easiest way to tell them apart is by size. Adult threadfin shad may reach five to seven inches, but most are one to two inches long, while adult gizzard shad typically range from four to 14 inches. The threadfin also has a yellow tail and a protruding lower jaw.

Photos courtesy of U.S. Army Corps of Engineers

Shad are an important baitfish in TVA-managed reservoirs, but—because shad are a prolific species and can repopulate quickly—fisheries biologists agree that die-offs have little impact on the overall fish population in most reservoirs. In fact, in smaller reservoirs, shad die-offs may be beneficial in controlling the shad population.

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.

 

 

 

           
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