Introduced clupeids in a southern reservoir: more evidence for system-specific reproductive styles

Abstract

Latitudinal trends in reproductive characteristics are evident for some species of Clupeidae. However, selection for life history styles may operate at the population level. The reproductive cycles of alewifeAlosa pseudoharengus and threadfin shadDorosoma petenense in Dale Hollow Reservoir, Tennessee, were monitored over two spawning seasons on the basis of a gonadosomatic index (GSI). Inshore movements normally associated with spawning migrations were monitored using gill nets in spring 1989. GSI values peaked for both species at least one month earlier in 1989 than in 1988 due to warmer water temperatures earlier in the year. Highest GSI values for female alewife occurred each year when surface water temperatures were about 20° C; threadfin shad GSI values peaked at temperatures of 22°–26° C. Trends in male GSI values in both species were similar to those in females. Alewives were not abundant in warm (> 22° C), shallow water after 1 May 1989, but alewife GSI values remained high after this date, suggesting that elevated inshore temperatures limited alewife reproduction. All aspects of alewife reproduction were comparable to other populations of alewife but did not follow latitudinal trends. Threadfin shad reproductive characteristics were similar to other published accounts. We suggest that thermal regimes and reservoir trophic status are important factors for clupeid reproduction and population-level analysis is suggested when considering reproductive styles. Further, our ability to predict the ecology of introduced species in freshwater systems is impaired when species considered have not coevolved or evolved in marine environments.