Change in Piscivore Growth Potential after the Introduction of a Nonnative Prey Fish: a Bioenergetics Analysis

The introduction of additional forage fish species to enhance sport fisheries is a common management strategy in lakes and reservoirs. However, illegal introductions occur without consideration of all potential ecological consequences. Introduction of Blueback Herring Alosa aestivalis as a forage fish to enhance recreational fisheries has been controversial, with several illegal introductions documented in the southeastern United States. We quantified the caloric density of introduced Blueback Herring and native Threadfin Shad Dorosoma petenense in Lewis Smith Lake, Alabama, to determine their potential values as prey to piscivorous fish. Caloric density estimates were then incorporated into bioenergetics simulations for Largemouth Bass Micropterus salmoides, Alabama Bass Micropterus henshalli, and Striped Bass Morone saxatilis to estimate their growth potential given different diet compositions. Piscivore diet composition from before the introduction of Blueback Herring was also incorporated into bioenergetics simulations for comparison with post‐introduction scenarios. Caloric density of Blueback Herring was higher than that of Threadfin Shad across all seasons, and consequently, bioenergetics simulations predicted increased growth potential for Largemouth Bass, Alabama Bass, and Striped Bass with increased proportions of Blueback Herring in their diets. The simulated growth effect of shifting consumption from Threadfin Shad to Blueback Herring was smaller for Largemouth Bass versus Striped Bass because Striped Bass were far more piscivorous than Largemouth Bass, with Alabama Bass intermediate. Simulated pre‐Blueback Herring piscivore diets resulted in less growth relative to what was observed for all post‐introduction simulations. Although Blueback Herring had higher caloric density values than Threadfin Shad, overall ecological impacts of their introduction are not yet fully understood and could likely also include negative impacts on these piscivores. As such, our findings represent one aspect of the overall, potentially complex effect of introduced Blueback Herring as an additional forage fish for piscivores.