Now that the population of double crested cormorants has been reduced in the Les Cheneaux Islands and perch numbers have begun to rebound, wildlife managers will focus on maintaining, rather than further reducing, the population of the predatory birds, now at about 500 nesting pairs.

The cormorant control program at Les Cheneaux is being used as a test case in the region.

Double crested cormorants have been a problem here since the 1980s, eating large numbers of perch over the years and depleting their population. Dave Fielder, research biologist with the Michigan Department of Natural Resources (DNR), said the perch mortality rate reached as high as 88% in 2003.

Over the past six years, the DNR and U.S. Department of Agriculture Wildlife Services have worked together to control the bird population to benefit the perch, a popular species with fishermen.

Mr. Fielder, who reported on the fish population status Saturday, May 2, at the Straits Area Regional Fisheries Workshop at Little Bear East Conference Center in St. Ignace, said the mortality rate for perch in the area was down from 88% to about 51% in 2008 as a result of the cormorant control efforts.

"That's probably the best evidence of what's driving the yellow perch population in terms of their ability to restore," he said.

The cormorant population in the islands is down about 90% since the program began in 2003, reported Tony Aderman of Wildlife Services, owing to efforts of the DNR and federal Wildlife Services. Owing to the decreased number of birds now preying on the fish, the two groups are switching from a reduction to a maintenance strategy to keep the bird population low. The number of cormorants in the area have been reduced from about 5,500 nesting pairs in 2004, to about 500 in 2008.

The goal of the program is to achieve a balance between the birds and fish, Mr. Aderman said.

"We want to try to maintain this 500 nesting pairs at Les Cheneaux, continue to monitor nesting colonies, continue with an adaptive management approach, and try to achieve a balance between the fisheries and cormorants," he said.

To control the number of cormorant nesting pairs, agents pour corn oil on the birds' eggs, physically move their nests out of the area, and use decoys to frighten the birds away. The eggs are oiled every 18 to 20 days, rather than crushed, to fool the birds into completing the gestation process and prevent them from simply laying more eggs, Mr. Aderman said.

"We use 100% corn oil to cover the eggs and it basically suffocates the embryo inside. The adult sits on a dead egg or a non-viable egg, but they don't know that, so they continue to sit on the egg until it's too late," he said.

A permit giving authority to the program to use lethal methods to control the cormorant population was recently extended an additional five years; it was set to expire at the end of last month.

About 1,800 birds were removed last year, Mr. Aderman said, from nesting colonies on Saddlebag Island, Crow Island, Goose Island, and St. Martin Island, as well as Green Island near St. Ignace. Nesting sites on Goose Island and Crow Island are now considered non-active as a result of these efforts.

The program in Les Cheneaux is the longest running cormorant control program in Michigan and its success is being used as a model for similar programs around the Great Lakes, including programs at Beaver Island, South Manitou Island, Thunder Bay, and Bay de Noc.

"We really don't know what's going to happen here, in Les Cheneaux. This is the longest running cormorant management project anywhere, so we don't know that the fish population getting better will attract more birds, or if we can actually keep it down to a level of 500 nesters," Mr. Aderman said.

Organizers of the fisheries workshop last weekend said 29 people registered for the all-day event, which included presentations on creel populations, programs monitoring prey fish and lampreys, herring rehabilitation in Lake Huron, and Atlantic salmon programs in the region. The workshop was sponsored by Michigan Sea Grant, Michigan State University Extension, DNR, Michigan Charter Boat Association, Michigan Steelhead and Salmon Fishermen's Association, Cheboygan Area Sportfishing Association, USGS Great Lakes Environmental Research Laboratory, and Lake Superior State University.