Population Trends of Walleye, Sauger and Double-Crested Cormorants in Lake of the Woods, Minnesota, 1968-2006

Double-crested cormorants Phalacrocorax auritus are a native species in the Lake of the Woods area.  Following settlement of the area in the late 1800s, cormorants were destroyed due to predation on commercially valuable fish populations.  The cormorant population was further reduced in the mid-1900s, likely due the widespread use of the insecticide DDT.  From 1956 through 1976, the nesting population of cormorants on the Minnesota portion of Lake of the Woods ranged from 100-130 pairs, Cormorant abundance increased under protection from the Migratory Bird Treaty, and the elimination of DDT use.  In the 1980s, biennial nest counts documented a rapid increase in cormorant abundance, which peaked in 1989 at 4,784 nesting pairs.  From 1990 through 2006 cormorant abundance remained stable between 2,852 and 4,378 nesting pairs.   Trends in the walleye Sander vitreus and sauger S. canadensis populations were compared to trends in the cormorant population.  No relationship between the year class strength or overall abundance of walleye and sauger and cormorant abundance could be demonstrated.  At current levels of cormorant abundance, it appears that cormorants are not negatively impacting walleye and sauger populations on the Minnesota portion of Lake of the Woods.