Cormorants can impact fish populations
Ann Arbor, MI — Many have speculated that the explosion in abundance of the fish eating cormorant was impacting fish populations in the Great Lakes. New research confirms that trends in cormorant numbers best explain the collapse of yellow perch in the Les Cheneaux Islands region of Lake Huron. Between 1980 and 2004 cormorants went from zero to over 5,500 nests (about 14,000 birds). Previous research there concluded that the birds had no appreciable effect on the perch population. This current study makes use of more recent information and clearly establishes that trends in cormorants most accounts for the collapse of the perch fishery.
The research conducted by the Michigan Department of Natural Resources' Fisheries Division made use of long term netting surveys and creel survey data to demonstrate that more than any other factor, cormorants account for the trends in the perch population over the time period examined. Dave Fielder, Fisheries Research Biologist for the DNR, reports, "I examined trends in perch reproduction, weather variables, water levels, and fishing activity. None of those factors were as influential as cormorant predation in contributing to the collapse of the perch population."
Fishermen have long complained about the effects of cormorants on Great Lakes fish populations.Its only been recently that scientists have had a sufficient data over time to be able to test some of these questions. Exact methods for establishing cause and effects of cormorant predation have also been lacking. However, this is beginning to change with the publication of studies such as this one.
Findings of this work led to a cormorant control effort in the Les Cheneaux Islands implemented by the USDA's Wildlife Services. Fielder has continued his monitoring and expects to publish again soon on how the perch population and fishery responded to the decline in cormorant numbers stemming from the management efforts.
"While fish abundance is a result of many different factors, we have learned that the rise of an abundant predator like cormorants can, in fact, substantially reduce some fish populations," said Fielder. These findings can now be further tested by examining the trends since 2004 as cormorant numbers are reduced.
Original Publication Information
Results of this study, "Examination of Factors Contributing to the Decline of the Yellow Perch Population and Fishery in Les Cheneaux Islands, Lake Huron, with Emphasis on the Role of Double-crested Cormorants," are reported by David G. Fielder in the latest issue (Volume 34, No. 3, pp. 506-523) of the Journal of Great Lakes Research, published by the International Association for Great Lakes Research, 2008.
Contacts
For more information about the study, Fielder, Michigan DNR, Alpena Fisheries Research Station, 160 E. Fletcher, Alpena, MI 49707; , (989) 356-3232 x2572.
For information about the Journal of Great Lakes Research, contact Marlene Evans, Editor, National Water Research Institute, 11 Innovation Boulevard, Saskatoon, SK, S7N 3H5, Canada; editor@iaglr.org; (608) 692-1076.
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Since 1967, IAGLR has served as the focal point for compiling and disseminating multidisciplinary knowledge on North America's Laurentian Great Lakes and other large lakes of the world and their watersheds. In part, IAGLR communicates this knowledge through publication of the Journal of Great Lakes Research, available to members in print and electronic form. A searchable archive of the journal is available online and includes the abstracts of articles from the journal's inception in 1975 through the most recent issue. In addition, complete articles are available to members who have signed up for an electronic subscription.