Facts & Figures

• The total Great Lakes population of breeding cormorants in the year 2000 was estimated at 230,000 adults. This number does not include sub-adults/juveniles, or young of the year. (Source Weseloh et al. 2002. J. Great Lakes Res. 28 (2): 125 - 144.)



• The average annual rate of change was about 14% in Lake Ontario from 1990 to 2000. At this annual rate of change, the Lake Ontario population will double every five years.



• Given the time fish spend in the basin (average 120 days), at a pound of fish/bird/day, this population consumes approximately 43 million pounds of fish per year.



• Consumption estimates suggest that cormorants may be consuming 40-60% of forage in eastern Lake Ontario.



• Cormorants are spreading inland and establishing colonies on systems such as the Kawarthas and Nipissing, among others.



• There are now about 200 nesting colonies of cormorants in the Canadian Great Lakes.



• Recent studies on Oneida Lake in New York State by Cornell University have shown major impacts on walleye and yellow perch. This study showed a 58% reduction in the survival of juvenile walleye and yellow perch directly linked to cormorant predation. (Rudstam et al. 2003. Ecological Applications.)



• Overpopulations of cormorants destroy valuable vegetation, including rare Carolinian vegetation.



• Overpopulations of cormorants harm other colonial waterbirds, such as herons.