Effects on Sport Fish Growth of Spatial and Temporal Variation in Age-0 Gizzard Shad Availability

Abstract

Availability of age-0 gizzard shad Dorosoma cepedianum and length increments of piscivorous sport fishes (black crappies Pomoxis nigromaculatus, white crappies P. annularis, largemouth bass Micropterus salmoides, and white bass Morone chrysops) were measured in five large Missouri reservoirs over several years to determine the effect of prey availability on sport fish growth. Two measures of prey availability were used: mean available age-0 gizzard shad biomass (GB), estimated from predator–prey size relationships, and mean fall total length of age-0 gizzard shad (GTL). These two measures were only correlated for age-1, -2, and -3 black crappies and age-1 white crappies. Annual length increments of age-classes of crappies and largemouth bass tended to increase asymptotically with GB; length increments increased linearly for age-2 white bass. Relationships between GB and sport fish length increments were relatively strong for crappies and weak for largemouth bass and white bass. The second measure, GTL, was correlated with length increments of crappies and age-1 largemouth bass. This index was much simpler to estimate than GB and may prove useful in predicting growth of small sport fishes. Prey availability helped explain differences in growth of sport fishes among reservoirs and years and it should be considered before attempts are made to increase sport fish densities through stocking or restrictive harvest regulations.