Effects of Commercial Exploitation on Common Carp Populations: Evidence of Compensatory Mechanisms?

Common carp Cyprinus carpio is one of the most abundant and detrimental invasive fish in North America. Mechanical removals are often attempted as a method to control common carp populations, but information regarding population level responses to exploitation are lacking. Because fish populations can be regulated by density-dependent mechanisms, overcompensation may occur when common carp are exploited resulting in increased recruitment and growth and decreased natural mortality, hindering manager’s ability to reduce population abundance. We used a combination of modeling and field experimentation to evaluate how carp populations respond to exploitation in three South Dakota natural lakes. A five year mark-recapture study occurred from 2007-2011 in three interconnected lakes to evaluate if commercial fishermen could regulate carp populations. Nearly 225,000 individuals were harvested from the three lakes over five years, representing 1 to 43% annual exploitation.  Despite high exploitation in some years, population estimates did not decrease during the study. Common carp survival in these three systems ranged between 54-79% and was related to commercial harvest, but harvest-related mortality appeared to be compensatory rather than additive. Emigration among lakes was relatively low but varied among years with the highest emigration occurring in 2010 when water levels were high. Common carp recruitment and growth has remained relatively unchanged since 2007. These results indicate that common carp control is difficult in large interconnected systems due in part to compensatory mortality and, to a lesser extent, interbasin movement patterns.