Simulated Population Responses of Common Carp to Commercial Exploitation

Common carp Cyprinus carpio is a widespread invasive species that can become highly abundant and impose deleterious ecosystem effects.  Thus, aquatic resource managers are interested in controlling common carp populations.  Control of invasive common carp populations is difficult, due in part to the inherent uncertainty of how populations respond to exploitation.  To understand how common carp populations respond to exploitation, we evaluated common carp population dynamics (recruitment, growth, and mortality) in three natural lakes in eastern South Dakota.  Common carp exhibited similar population dynamics across these three systems that were characterized by consistent recruitment (ages 3 to 15 years present), fast growth (K = 0.37 to 0.59), and low mortality (A = 1 to 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 with a 575-mm length restriction, representing commercial gear selectivity.  Simulated common carp size structure modestly declined (9 to 37%) in all simulations.  Abundance of common carp declined dramatically (28 to 56%) at low levels of exploitation (0 to 20%) but exploitation >40% had little additive effect and populations were only reduced by 49 to 79% despite high exploitation (>90%).  Maximum lifetime egg production was reduced from 77 to 89% at a moderate level of exploitation (40%), 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 to how 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 perturbations induced by this invasive species.