FATE OF DEAD FISH IN A SMALL LAKE

Observations and experiments were conducted on natural mortality of fi sh at a small Michigan lake during spring. During an extensive fish di e-off in 1989, only 22% (202) of the dead fish were found el en though an estimated 10% (918) of the fish population >150 mm TL died. Scaven gers, principally yellow bullheads (Ameiurus natalis) and turtles feed ing in the littoral zone, claimed approximately 60% of the dead fish t hat year and 82% in another year with a smaller die-off. The remainder decomposed in 6-34 days. The long-standing mystery of why so few larg e dead fish are noticed in lakes, despite high annual natural mortalit y rates of abundant fish populations, was adequately explained by unse en decomposition in deep water and the ability of resident scavengers to keep up with the supply of dead fish except during unusually concen trated fish die-offs.