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

Abstract

Impacts of double-crested cormorants (Phalacrocorax auritus) to fi sheries have been documented, but evaluation of the process and outcomes of cormorant management to reduce impacts on fiis 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 fl avescens) population and fi shery. 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 fi sheries and increase fi sh populations. At each location, management efforts reduced cormorant foraging, and fi shery data indicated increased abundance of sport fi sh species. The 3 locations combined provided evidence for the underlying hypotheses that cormorants can infl uence mortality of local sport fi sh 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 fi sheries through cormorant management is sustainable.