Evaluating the Potential for Predatory Control of Gizzard Shad by Largemouth Bass in Small Impoundments: A Bioenergetics Approach

Abstract

Gizzard shad Dorosoma cepedianum is an important fish species that can have strong effects on aquatic communities throughout the southeastern and midwestern USA. Gizzard shad often become overabundant, competitively reducing growth and recruitment of sport fishes. Using field data and bioenergetics simulations, we evaluated the potential for largemouth bass Micropterus salmoides to control the abundance of gizzard shad in small impoundments. We sampled 1,313 largemouth bass stomachs, of which 66% contained prey, from four ponds during 1998 and 1999. Large (≥350-mm) largemouth bass consumed the greatest biomass of gizzard shad, eating gizzard shad throughout most of the year. Gizzard shad were more abundant in the stomach contents of largemouth bass less than 350 mm long during late summer and early fall than during winter and early spring. Variation in the mortality of predatory largemouth bass (21% versus 31%), as estimated from weighted catch-curves, resulted in only slight variation (6–7%) in estimates for total annual consumption of gizzard shad. Using population estimates from the ponds, we considered three predator densities (low = 49/ha; intermediate = 172/ha; and high = 351/ha) in our simulations. Bioenergetics simulations suggested that largemouth bass populations in these ponds at intermediate and high densities could annually consume between 50 and 186 kg/ha of gizzard shad. Comparison of an estimated range of age-0 gizzard shad abundances and bioenergetics estimates of predator consumption indicated that largemouth bass predation could regulate the abundance of age-0 gizzard shad in small ponds.