Regulation of Growth and Mortality in Larval Bluegills: Implications for Juvenile Recruitment

Factors related to growth and survival of 10‐d cohorts of larval bluegills Lepomis macrochirus were examined in two small impoundments via daily growth increments on otoliths. Successful spawning occurred from April through September, producing peak larval densities greater than 360 fish/m3. Larval bluegill density was negatively correlated with zooplankton density in both ponds, suggesting that larvae reduced zooplankton abundance via predation. Several variables were related to larval growth and mortality. Cohorts whose larval densities were low tended to have faster growth and higher survival than cohorts with high larval densities. The mechanism responsible for this density‐dependent relation was not clear in all instances; however, some evidence suggested that control occurred via intraspecific competition for zooplankton. Relative survival of larval bluegills to the juvenile stage was negatively correlated with limnetic larval fish density; however, no relations were detected between larval survival and juvenile recruitment across cohorts, suggesting that juvenile recruitment was set at larval sizes larger than those we examined. Larval growth was negatively correlated with larval mortality in one pond. Evidence for size‐selective mortality existed for late‐spawned fish, with selection favoring small‐bodied larvae. We suggest that growth and mortality of larval bluegills are influenced by larval abundance and intraspecific competition for zooplankton when resources are limiting; however, recruitment of juveniles did not appear to be set during the larval stage.