Simulated Population Responses of Common Carp to Commercial Exploitation

Common carp Cyprinus carpio is a widespread invasive species that can become highly abundant and have deleterious ecosystem effects. Thus, aquatic resource managers are interested in controlling common carp populations, but control is difficult, in part, because of the inherent uncertainty as to how populations respond to exploitation. To better understand this response, we evaluated the population dynamics (recruitment, growth, and mortality) of common carp in three natural lakes in eastern South Dakota. Common carp exhibited similar population dynamics across these three systems, which were characterized by consistent recruitment (ages 3-15 being present), fast growth (K = 0.37-0.59), and low mortality (A = 1-7%). We then modeled the effects of commercial exploitation on size structure, abundance, and egg production to determine its utility as a management tool to control populations. All three populations responded similarly to exploitation simulations in which a 575-mm length restriction represented commercial gear selectivity. Simulated common carp size structure declined modestly (9-37%) in all simulations. The abundance of common carp declined dramatically (28-56% of starting levels) at low levels of exploitation (0-20%), but exploitation greater than 40% had little additive effect, the final populations only being reduced 49-79% despite high exploitation (>90%). At a moderate level of exploitation (40%), maximum lifetime egg production was reduced to 77-89% of starting levels, indicating the potential for recruitment overfishing. Exploitation further reduced common carp size structure, abundance, and egg production when simulations were not size selective. Our results provide insights into the ways in which common carp populations may respond to exploitation. Although commercial exploitation may be able to partially control populations, an integrated removal approach that removes all sizes of common carp has a greater chance of controlling population abundance and reducing the perturbations induced by this invasive species.