Management of double-crested cormorants to improve sport fisheries in Michigan: three case studies

Impacts of double-crested cormorants (Phalacrocorax auritus) to fisheries have been documented, but evaluation of the process and outcomes of cormorant management to reduce impacts on fisheries is lacking. We provide a synthesis of adaptive management of double-crested cormorants in the Les Cheneaux Islands (LCI), Brevoort Lake, and Drummond Island, Michigan from 2004 to 2007. The LCI management focused on reducing numbers of nesting cormorants in the region as a means of improving the yellow perch (Perca flavescens) population and fishery. At Brevoort Lake and Drummond Island, management focused on lethal and nonlethal harassment of spring migrating cormorants to reduce their foraging on spawning walleye (Sander vitreus) and yellow perch and to improve those fisheries and increase fish populations. At each location, management efforts reduced cormorant foraging, and fishery data indicated increased abundance of sport fish species. The 3 locations combined provided evidence for the underlying hypotheses that cormorants can influence mortality of local sport fish populations and that short-term management goals have been met. Continuation of adaptive management and monitoring programs will determine whether the improvement of targeted sport fisheries through cormorant management is sustainable.