Trophic state differences in population characteristics of gizzard shad in two tennessee river impoundments

Abstract

Gizzard shad Dorosoma cepedianum population characteristics, including relative abundance, size structure, growth, body condition, and mortality were compared between Guntersville and Wheeler Reservoirs, two Tennessee River impoundments. Fish were collected with DC electrofishing and water quality was sampled along upstream to downstream longitudinal gradients in each reservoir from October 1995 through August 1996. Chlorophyll-a concentrations and gizzard shad abundance were higher in Wheeler than in Guntersville Reservoir. Neither chlorophyll-a concentrations nor gizzard shad a bundances showed a longitudinal gradient from upstream to downstream in either reservoir. However, a gradient of increasing water clarity was evident in both reservoirs that was associated with poorer gizzard shad body condition. In Guntersville Reservoir, where gizzard shad abundance was lower, the population was comprised of older and larger fish that exhibited faster growth and higher body condition. Gizzard shad were more abundant in Wheeler Reservoir, and fish displayed slower growth, poorer body condition, and potentially greater exposure time to predation. Hence, survival was lower as this population was comprised of a higher proportion of younger fish than in Guntersville Reservoir. Trophic state differences among reservoirs were related to differences in gizzard shad population characteristics and likely influenced the role of these fish as a prey species. © 2002 Taylor & Francis Group, LLC.