Potential vulnerability of black bullheads to multiple predators in small impoundments: implications for biological control

Abstract Overabundant species can alter a fish community and negatively influence recreationally important species. Introducing new or more predators into a system to control such nuisance fish has been met with limited success and may involve some risk. Understanding to what degree consumption of nuisance species occurs by existing predators and whether an existing predator community is physically capable of consuming the nuisance species can help to determine whether biological control may be possible without new introductions of predators. The objectives of this study were to: (1) document consumption of black bullheads Ameiurus melas by three predators; and (2) determine the relative vulnerability and potential ingestion of bullheads by these predators. We used gastric lavage monthly from May through September to collect stomach contents of channel catfish Ictalurus punctatus, largemouth bass Micropterus salmoides, and walleye Sander vitreus in four reservoirs to calculate the percent occurrence of black bullheads in predator stomachs. We also collected various sizes of juvenile black bullheads to measure body width and depth, with and without the pectoral and dorsal spines extended, respectively. This information was coupled with measured gape widths from the predators to calculate relative vulnerability curves and probabilities of ingestion based on predator size. Black bullheads were rarely consumed by the three predators, and stomach contents generally contained a single black bullhead when consumption did occur. Relative vulnerability based on body depth was similar for all three predators. Potential ingestion was similar among all three predators but was higher for channel catfish compared to the other two predators when black bullhead depths were measured with the dorsal spines extended. This study provides new information about the potential for biological control of black bullheads by an existing predator community.