We examined fish populations, limnological conditions, lake basin morphology and watershed characteristics to evaluate patterns in population characteristics of ecologically important fish species in relation to environmental conditions in agriculturally eutrophic lake systems. Fish populations and environmental characteristics were sampled from 129 Iowa lakes using standard techniques from 2001-2006. Lakes with high catch rates of common carp (Cyprinus carpio) had high nutrient concentrations, high phytoplankton biomass and low water transparency. In addition, lakes with high catch rates of common carp had low catch rates of important sport fishes including bluegill (Lepomis macrochirus), largemouth bass (Micropterus salmoides), black crappie (Pomoxis nigromaculatus) and white crappie (P. annularis). The relationship between common carp and sport fishes appeared to function as an ecological threshold. Specifically, when common carp catch rates were >2 kilograms per fyke net night, catch rates of sport fish were always low and water quality in the study lakes was poor. Shallow systems (natural lakes, oxbows) had higher densities of common carp compared to deeper systems (impoundments, surface mines), thereby suggesting that shallow lakes are most sensitive to the effects of common carp and that restoration efforts incorporating biomanipulation of common carp will likely be most successful in shallow systems.
Bibliographical noteFunding Information:
Data were provided by the Iowa Department of Natural Resources Fisheries Bureau and the Iowa State University Limnology Laboratory. Special thanks to E. Thelen for aging the majority of fish used in this study. We also thank D. Bonneau, M. Conover, T. Gengerke, M. Hawkins, J. Koch, J. Morris, D. Rowe and R. Schultz for useful discussions associated with this project. M. E. Colvin, J. Fischer, R. Harr, J. Koch, J. Morris, T. Neebling and four anonymous reviewers provided helpful comments on a previous version of the manuscript. Funding was provided by Iowa Department of Natural Resources and the Department of Natural Resource Ecology and Management at Iowa State University.
- alternative stable states
- ecological thresholds
- water quality