Source-sink population structure of invasive common carp in a model Midwestern watershed: empirical evidence and notes on management

Abstract

Effective management of invasive fishes requires a detailed understanding of the factors that influence population structure and persistence across relevant spatial and temporal scales. It has been hypothesized that the common carp <italic>(Cyprinus carpio)</italic> is often invasive in the North American Midwest due to its propensity to utilize shallow, predator-free basins as productive nursery habitat. Although it has been demonstrated that such basins often support extremely high abundances of young carp, the fate of these carp is unknown. To determine whether these putative nurseries serve as important sources of recruits at a watershed scale, we used mark-recapture and genetic assignment methods to investigate carp recruitment in a system of interconnected lakes, ponds, and associated wetlands in central Minnesota. Annual trap net surveys in 4 lakes and 8 ponds in the Phalen Chain watershed from 2009-2013 revealed that young-of-year carp were found exclusively in shallow pond habitats. Mark-recapture studies in 2011 and 2012 indicated that, of the 613 carp marked in one of the putative nursery ponds, ~31% of recaptured carp (25 of 80) had emigrated from the nursery pond to a connected water body. Microsatellite analysis of carp tissue samples (n=1041) from all basins throughout the watershed and from individuals moving between lakes and putative nurseries during the spawning season revealed two genetically distinct strains of carp within the watershed. The distribution and movements of genetically distinct carp revealed patterns in dispersal and colonization consistent with the carp nursery hypothesis (i.e. source-sink population structure). Additionally, there was evidence of reproductive homing by adult common carp. Our results and continued research on carp recruitment dynamics will aid in the development of population models and integrated pest management strategies to combat this highly invasive species.