Compensatory response of invasive common carp Cyprinus carpio to harvest

- Harvest mortality can be additive or compensatory.
- Type of mortality can influence success of invasive species removal programs.
- We evaluated response of common carp to intensive removal efforts.
- Carp abundance, growth, and recruitment remained stable despite high harvest in some years.
- Survival declined with increasing harvest, but suggested a compensatory response.
- Compensatory responses limit managers ability to control invasive populations through mechanical removal.

Invasive species are often mechanically removed to reduce or eliminate their populations. However, removal may release survivors from density-dependent mechanisms resulting in stable or increasing population abundance through compensatory processes. Additionally, immigration of new individuals into systems where removal is occurring may negate efforts to control population abundance. Thus, understanding population-level responses to removal and immigration rates are essential aspects of invasive species management. We evaluated how common carp Cyprinus carpio populations respond to removal through commercial harvest in three interconnected lakes over five years. Nearly 230,000 common carp (up to 55 fish/ha/year) were removed and exploitation rates ranged from <1 to 43% across three lakes over four years. Despite high removal rates in some years, carp population abundance, recruitment, and growth remained stable. Carp survival ranged between 54-79% and was inversely related to removal rate. However, survival only decreased by 25% at 43% exploitation, suggesting a partial compensatory rather than additive response. Emigration among lakes was low (<1%; >2000 carp), but varied among years in response to water level fluctuations. Our results indicate that carp control is difficult in large interconnected systems due to compensatory mortality and interbasin movement patterns, limiting the ability of removal-based management practices alone to control these invasive populations.