Cooperative Effort Restores Walleye Fishery in Brevoort Lake

Record walleye production follows cormorant control on Hiawatha

Story submitted by Chuck Bassett, Fisheries Biologist (906) 789-3336

A cooperative effort involving the US Forest Service, Michigan Department of Natural Resources, USDA Wildlife Services, Lake Superior State University, the Straits Area Sportsmen's Club, and the Brevoort Lake Association is restoring a depleted sport fishery and expanding knowledge on how avian predators influence fish populations.

The number of fish available for anglers to catch reflects a balance between the number reproduced and the number that are removed by predators and other natural sources of mortality. Increasing mortality caused by rising numbers of predators can substantially reduce numbers of fish available for anglers.

That is what happened in 4,230-acre Brevoort Lake located on the East Unit of the Hiawatha National Forest in Michigan. The culprit: exploding populations of the double-crested cormorant, a large, dark-colored bird that typically consumes about 1.5 lbs of fish daily (U.S. Fish and Wildlife Service data). Between the mid-1980s and 2005, numbers of cormorants feeding on the lake during the annual spring migration increased from just a few to over 600 that consumed tens of thousands of pounds of fish.

As the cormorant population grew, Forest Service fishery assessments found that numbers of adult walleye in the lake declined from about 8500 in 1986 to 1200 in 2005. This occurred despite large investments made by the Forest Service and Michigan DNR in habitat improvement and fish stocking. Less than 1 percent of naturally reproduced and stocked walleye were surviving to adult size.

Anglers reported that numbers of large yellow perch also declined sharply. By the late-1990s, the once popular fishing destination was receiving relatively little use. Similar declines in sport fisheries were occurring elsewhere in the Great Lakes Region where cormorant numbers increased several-fold.

Following discussions among Federal, State and local officials, a cormorant "harassment" program was initiated on Brevoort Lake in 2005, under the supervision of USDA Wildlife Services. Local trained "agents" (Lake Association and Sportsmen's Club members) provided dawn to dusk "harrassment" consisting of non-lethal and limited lethal methods for about 30 days following ice-out. All activities and numbers of birds observed and taken were carefully recorded.

As a result of the volunteer patrols, numbers of cormorants on the lake declined from a daily average of 690 in 2005 to 127 in 2007. An estimated 26,600 lbs of fish consumption was prevented in 2005 (USDA Wildlife Services data). A study of cormorant stomach contents conducted by students from Lake Superior State University under the guidance of Dr. Ashley Moerke indicates that in 2005, cormorants on Brevoort Lake consumed more than 1400 young walleye and 108,000 yellow perch during a 30 day period.

Consumption at this level or higher had occurred for at least a decade. It's easy to understand why fishing success for these species declined!

Has the control effort resulted in higher numbers of walleye and perch for anglers? Forest Service assessments found that between 2005 and 2008, numbers of adult walleye in the lake increased more than five-fold. The current population of about 7800 is just slightly lower than the peak numbers found in 1986. Age 3 fish (2005 reproduction) make up about 90 percent of the current population, and are more than twice as abundant as any previously documented age 3 yearclass. Anglers report much improved fishing for large perch.

Are these improvements in fish abundance just coincidence? Maybe, but not likely. The historic 2005 yearclass of walleye is the first in at least 15 years to be largely unhindered by cormorant predation. It appears the balance has been tipped back in favor of more fish for anglers.