Population Trends and Colony Locations of Double-crested Cormorants in the Canadian Great Lakes and Immediately Adjacent Areas, 1990–2000: A Manager's Guide

Numbers of nests of double-crested cormorants (Phalacrocorax auritus) were censused at up to 190 colonies in the early- mid- and late-1990s and 2000 on the Canadian Great Lakes and immediately adjacent U.S. waters. During those four periods, the number of nests increased from approximately 21,000 to 49,000 to 55,000 to 76,000. The total Great Lakes population of breeding cormorants for 2000 is estimated at 115,000 pairs (=nests). For the first time, all colony locations were plotted on lake-wide maps. Major nesting areas were eastern Lake Ontario, western Lake Erie, eastern Georgian Bay, all of the North Channel, and western Lake Superior. Average annual growth rates from the early 1990s to 2000 were much lower for most areas than during the 1980 to 1990 period. Three cormorant management issues are discussed: cormorant impacts on vegetation, on other colonial waterbirds, and on fisheries.