A whole-lake density reduction to assess compensatory responses of gizzard shad Dorosoma cepedianum

Abstract

We used a fishery-induced density reduction of gizzard shad Dorosoma cepedianum at a previously unharvested lake to evaluate compensatory density dependence in recruitment processes. We also studied gizzard shad populations at two nearby unharvested lakes to provide contrast with the harvested population. Gizzard shad spawner biomass was reduced by 72% at the harvested lake after 2 years of gill-net removals, although variation in total shad biomass was more modest. We evaluated responses by gizzard shad to the range of biomasses present among the three lakes and 5 years of the study. Annual growth increments varied little over 5 years and were not related to population density across the three lakes. Length-at-maturity differed among lakes and years, but was not related to population density. Despite the range in spawner biomass among the lakes during the study, annual recruitment estimates showed little relationship to the size of the spawner population, suggesting density-dependent prerecruit survival. A spawner–recruit analysis on pooled data from the three lakes indicated that prerecruit survival was negatively related to spawner biomass. Our study provides a rare glimpse of fish compensatory responses following exploitation of a previously unharvested population and has implications for population dynamics theory and fisheries management.