Threadfin shad, Dorosoma petenense Günther, mortality: causes and ecological implications in a South-eastern United States reservoir

Cold stress was identified as an important factor influencing both reservoir‐wide mortality and impingement of threadfin shad, Dorosoma petenense, during the period October 1976 to April 1977 in Watts Bar Reservoir, Tennessee. Relative numbers and size frequency of impinged threadfin shad were similar to the relative numbers and size frequency of shad preyed upon by sauger, Stizostedion canadense, and skipjack herring, Alosa chrysochloris. This relationship implies that the factor mainly responsible for impingement, low temperature, also influences prey vulnerability. Threadfin shad made up 99% of the combined diet of sauger and skipjack herring from November until the threadfin shad disappeared in January. These predators did not readily switch to alternative prey in the short term, but by the next autumn 25–100% of the diet was alternative prey. Reappearance of threadfin shad the year following mass mortality and ability of the predators to vary their diet emphasize the resilient nature of some predator‐prey systems.