People wondering just how big the cormorant colony off the Ludington Pumped Storage Plant is now have their answer. Officials from the Department of Natural Resources and USDA Wildlife Services on Thursday counted 486 nests averaging about four eggs each.

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Assuming two adult birds for every nest and adding in immature birds that are present, but can’t breed, officials estimated there are potentially 2,000 birds living just south of Ludington for about 150 days each year.

The survey is significant because the birds have been blamed for hurting local alewife stocks and have been observed gobbling up stocked brown trout in Ludington Harbor in recent years. Charter captains and perch anglers for the last few years have begged officials to inventory the colony.

DNR Fisheries Biologist Supervisor Tom Rozich answered their call Thursday when he accompanied Pat Ryan and Greg Rigney of USDA Wildlife Services on a trip to inventory the colony on the breakwall off the plant co-owned by Consumers Energy and Detroit Edison. The group was shuttled to the breakwall by Underwater Construction Corp., the contractor responsible for maintaining the fish barrier net that surrounds the area.

The 1,850-foot breakwall, made of huge slabs of limestone, isn’t quite covered from one end to the other with double-crested cormorant nests, but the birds have nested on most of the flat surfaces and convenient crevices on the east side of the reef that runs from north to south in Lake Michigan. The structure — located 2,700 feet offshore — was designed to keep wave heights in the area down to four feet or less.

A typical nest made of sticks, grasses, reeds, string, rope and even fishing tackle included four eggs or young birds. The eggs were bluish in color and about the size of chicken eggs, while the young birds ranged from the size of a robin to more than a foot in height.

With the rocks that make up the structure ranging in height from five to 15 feet above water level, the going was rough. Rozich and Ryan, a wildlife biologist, scrambled along ridges slick with droppings while spraying a corner of each nest with water-soluble orange paint to show it had been counted.

Ryan, soaked in sweat like his co-workers, said it was the most labor-intensive colony survey he’d been a part of.

“All of the rock-hopping makes it a little harder than normal,” he said.

Making things more difficult was the presence of older hatchlings that weren’t quite fledged. The biologists took care not to get too close to those birds, because Ryan said the birds would jump from the high rocks. The birds remain a protected species under the migratory bird treaty between the United States and Canada.

As they sprayed each nest, biologists shouted out numbers ranging from zero to seven so that Rigney could note the population of the reef.

No eggs, birds or nests were harmed by the crew, but at least one herring gull gobbled up a young cormorant as its parents left the nest.

Rozich has said previously that he believes the colony to be an unnatural situation since the reef is a man-made structure. He would like the colony eliminated.

Ryan said the colony is about what he expected to find, based upon the anecdotal reports that prompted the survey. He said the reef would be a convenient location to control cormorant breeding because it is more convenient to reach than some of the islands in the Great Lakes that are six or seven miles offshore. Currently, USDA Wildlife Services is practicing some type of cormorant population control in the Les Cheneaux Islands, Thunder Bay near Alpena and in the Bays de Noc.

Double-crested cormorants are native to Michigan, but most biologists believe they never reached the population levels they currently enjoy on the Great Lakes, even before they were decimated by birth defects linked to pesticides in the 1960s. Since DDT was banned, cormorants have come back stronger than ever and are being blamed for reducing stocks of perch, smallmouth bass, walleyes and alewives in different locations around the Great Lakes.

Cormorants can’t be controlled by destroying nests because they’ll simply lay more eggs within 36 hours after the original nest is destroyed, Ryan said. The ideal solution for many areas is spraying eggs with corn oil, which Ryan said has limited reproduction to almost nothing in the Les Cheneaux Islands.

But to be effective, corn oil must be applied every two weeks from May through September.

Without controls, cormorants can breed after reaching two or three years of age, with eggs taking one month to hatch and young birds needing another month to fledge.

Other methods of control include harassing birds and even killing a few birds to dissuade flocks from nesting.

Rozich said for the USDA Wildlife Services to practice controls near Ludington, the DNR’s internal cormorant workgroup would need to approve funding, which he said he would request.

Doing some rough calculating, Rozich said 1,000 cormorants could eat about 1.2 million alewives per year if they ate only alewives — which they don’t. The birds’ diet varies from alewives and perch to crustaceans like crayfish.

Without predators, cormorants are living as long as 18 years of age in the Great Lakes region, Ryan said. He said he didn’t have any estimates for the survival of the hatchlings, but said for numbers to increase like they did over the last 15 years, survival rates would have to be good.

“I guess it’s about what we expected to find,” Ryan said. “The cormorants look very healthy, and there are a lot of eggs in each nest. There’s a possibility of controlling them in the future.”