Evaluating the Effects of Threadfin Shad on Larval Bluegill Recruitment in Recently-Stocked Small Impoundments

Threadfin shad are commonly stocked into small impoundments to increase the growth and condition of largemouth bass, ultimately to enhance recreational fishing. However, the effects of threadfin shad on largemouth bass and bluegill recruitment, growth, and condition are not fully understood, especially in small impoundments (e.g., <10 ha). In particular, few studies have examined the effects of threadfin shad on larval stages of other forage species such as bluegill. We evaluated the potential for competition between threadfin shad and larval bluegill in five recently-stocked small impoundments using zooplankton abundance data and diet analysis. Preliminary results from the first summer of pond surveys suggest that threadfin shad have the potential to reduce zooplankton abundance in late spring which may reduce larval bluegill survival. Prior to bluegill spawning, zooplankton abundances in small impoundments with threadfin shad declined from 209 to 2 zooplankton per liter while zooplankton abundances in impoundments without threadfin shad increased over this period. Subsequent winter seine data showed much lower juvenile bluegill densities in ponds with threadfin shad. Reduced larval bluegill survival may suppress year class strength and negatively impact the forage base for largemouth bass later in the season.