Ecology and Management of Superabundant Fish Populations

Fish population biomasses can reach extreme levels; we term these populations superabundant fish populations. Superabundant fish populations may negatively affect aquatic communities and anglers, necessitating the effective management of the superabundant fish populations. However, there are gaps in our understanding of these populations. The gaps in our understanding hamper our ability to predict effects on valuable sportfisheries and to effectively manage superabundant fish populations. The overall goal of my thesis research is to provide further insight into the ecology of superabundant fish populations and to provide information that will aid in their effective management. First, we described a new method for estimating abundances and biomasses of superabundant fish populations in lentic systems using generalized N-mixture models with data from consumer-grade sonar, vertical gillnets, and a boat electrofisher. These open population models use point-count data with covariates to estimate site-specific abundances and detection probabilities. I used this method to estimate that there were 1.1-1.4 million white perch (Morone americana) and 0.5-1.1 million gizzard shad (Dorosoma cepedianum) in Branched Oak Lake, Nebraska. Second, we determined how the spatial distributions of superabundant white perch populations related to the spatial distributions of gizzard shad populations present in the same waterbodies by using the site-specific abundances estimated with the generalized N-mixture models. White perch and gizzard shad spatial distributions were positively related in Branched Oak Lake and Pawnee Reservoir, Nebraska. We suspect that large population sizes and similar diets contributed to the observed relationship. Third, we evaluated the effect of a low-dose-rotenone application on white perch and gizzard shad populations in Pawnee Reservoir, Nebraska. The low-dose rotenone application in Pawnee Reservoir led to a large reduction (83%) in the white perch population biomass and extirpated, or nearly extirpated, gizzard shad from the reservoir. By filling in the gaps in our knowledge of superabundant populations we can more effectively manage them for the good of our fisheries resources and their users by improving growth and abundance of sportfish. Advisors: Kevin L. Pope and Christopher J. Chizinsk