Mortality brought on by chilly stress has been recognized as an element regulating the abundance of gizzard shad populations, notably in waters close to the northern fringe of the species’ distribution the place extended chilly winters would possibly nearly get rid of them. Sudden chilly spells inflicting water temperatures to drop a number of levels in already chilly water may cause large kills.

In a examine by Cornell College researchers, young-of-the-year gizzard shad have been held in cages in Oneida Lake, New York, through the winter previous to ice-up.* Shad had low mortality in water above 46°F and mortality was excessive in water lower than 39°F. Researchers additionally examined survival in chilly rooms underneath managed temperature remedies of 34°F, 36°F, and 39°F to simulate mid-winter circumstances. First, shad have been allowed to acclimate to 46°F, then the tank temperatures have been lowered by a couple of half of a level per day till the ultimate take a look at temperatures have been reached.

Mortality was low through the acclimation interval. A bigger proportion of shad survived for longer durations within the 39°F tanks and mortality was highest within the coldest tanks.


Inside every temperature remedy, small fish died sooner. The researchers additionally noticed that the common measurement of shad in area collections elevated via winter, indicating larger chilly tolerance of bigger people. They conclude that chilly stress and the shortcoming to acclimate to lowering temperatures, somewhat than hunger, are key elements in winter mortality.

These findings counsel that you could count on massive shad winterkills when extreme cold-fronts lower water temperatures rapidly in early winter earlier than ice-up. As soon as lakes are coated in ice and buffered extra from sudden adjustments in air temperatures, the severity of overwinter mortality ought to coincide with the period of the ice-cover interval.

*Fetzer, W. W., Brooking, T. E., J. R. Jackson, and L. G. Rudstam. 2011. Overwinter mortality of gizzard shad: Analysis of hunger and chilly temperature stress. Trans. Am. Fish. Soc. 140:1460-1471.

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