
Project Objectives
Common carp management can reduce a lake’s carp biomass and improve its water and floristic quality. However, project success can vary depending on multiple factors related to management, the carp population itself, and underlying lake characteristics. To further understand the effectiveness and potential benefits of common carp management, MAISRC researchers are studying the impacts of management on carp biomass, aquatic plant communities, and water quality in a diverse array of lake types and ecosystems across the state of Minnesota.
The goal of this project is to quantify the full range of common carp management effectiveness across several, diverse case studies to:
- Allow stakeholders and managers to set data-driven expectations for management success and
- Provide insight into the underlying factors that influence management success.
This project and resulting research products (dataset, data process and analysis code and workflow, management-focused report, and a peer-reviewed scientific publication) forms a foundation for adaptively managing water quality through carp biomass reduction.
Background
Common carp are known to disturb lake sediments and dislodge aquatic plants, which can alter a lake’s ecological makeup and adversely affect water quality. Common carp management can be an effective tool to improve water quality in some lakes, but the benefits are variable (Figure 1) and have been most often evaluated in shallow, unstratified lakes for which results may not be generalizable (Bajer and Sorensen 2015). Long-term improvements to water and floristic quality are often dependent on more than just carp response, so an understanding of carp management outcomes across a wider range of lake types and ecosystems could be used to more reliably prioritize lakes for carp management efforts that would measurably improve water and floristic quality.

Evaluating the effects of carp management in impaired lakes is complex and can be confounded by other, concurrent management efforts (Figure 2). Reducing biomass is often the focus of implementing carp management as well as evaluating its effectiveness, whereby success is defined as reducing the population below a specific threshold (e.g., < 100 kg/ha; Bajer et al. 2009). However, successfully reaching a biomass threshold does not necessarily lead to positive water and floristic quality responses, which are also dependent on context-specific interactions between lake processes, common carp, additional sources of nutrients, watershed characteristics, and other management efforts.
In partnership with the Minnehaha Creek Watershed District, the UMN research team is evaluating statewide data from common carp management projects to:
- Quantify diverse impacts of management efforts on common carp populations and
- Quantify diverse lake responses to carp management, especially regarding water quality and macrophyte community composition.

Activities and Progress
Evaluating common carp biomass responses: The project team is compiling and evaluating carp management efforts across the state. Reduction in carp biomass could be related to covariates such as lake area, littoral area (or proportion of littoral area), and shoreline development factor, which are also being collected. Thanks to contributions from carp management contractors, watershed districts, lake associations, and other stakeholders across the state, to date, the team has compiled carp biomass data from 80 lakes, carp removal data from 31 lakes (29 with corresponding biomass data), and carp commercial harvest data from 211 lakes (often no corresponding biomass data from harvest years).
Evaluating water and floristic quality responses: The project team is also evaluating the effects of carp management on water quality (e.g., total phosphorus, Secchi depth, and chlorophyll-a concentrations) and aquatic plant communities. Analyses of the aquatic plant community data have included species responses, floristic quality responses, and community responses. Covariates have included:
- lake depth
- nutrient concentrations
- pre-management water clarity
- lake morphological characteristics
- relevant management history (e.g., alum treatments)
- and watershed characteristics (e.g., size, watershed to lake area ratio, and land cover)
To date, the team has compiled water quality data from 64 lakes with carp removal or biomass data (Minnesota Pollution Control Agency, LAGOS Research Platform) and aquatic plant community point-intercept survey data from 53 lakes with carp removal or biomass data (Minnesota Aquatic Invasive Species Research Center “PI Charter App”).
References
Huser, B. J., Bajer, P. G., Chizinski, C. J., & Sorensen, P. W. (2016). Effects of common carp (Cyprinus carpio) on sediment mixing depth and mobile phosphorus mass in the active sediment layer of a shallow lake. Hydrobiologia, 763(1), 23–33. https://doi.org/10.1007/s10750-015-2356-4
Bajer, P.G., Sullivan, G. & Sorensen, P.W. Effects of a rapidly increasing population of common carp on vegetative cover and waterfowl in a recently restored Midwestern shallow lake. Hydrobiologia 632, 235–245 (2009). https://doi.org/10.1007/s10750-009-9844-3