Lakes Prone to Winter Hypoxia in Interconnected Systems Function as Nurseries for Invasive Common Carp

Recent research has revealed that one of the primary reasons why common carp can be extremely invasive in the North American Midwest is the propensity of adult carp to exploit interconnected lakes that winterkill as nurseries (Bajer and Sorensen 2010). To test this hypothesis we surveyed the fish communities of six interconnected lakes in central Minnesota in 2009, 2010, and 2011. Each year, young-of-the-year carp were only captured in the two basins that experienced winter hypoxia. Subsequent mark-recapture studies in those nurseries using trap-nets and boat electro-fishing revealed that the two lakes combined contained ~48,000 young-of-the-year carp in 2010, of which ~5,000 survived their first winter. To determine whether these highly productive basins may function as population sources to the entire watershed, we investigated emigration of juveniles through observational field studies using passive integrated transponder (PIT) technology coupled with controlled laboratory experiments on juvenile carp movement. Preliminary findings lend support to our hypothesis. Continued research will enhance our understanding of carp ecology in the Midwest and aid in the development of both population models and targeted management strategies to combat this highly invasive and destructive species.