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Cleaner Lake, Dirty Birds: Destructive Western Lake Erie Cormorants to Be Culled

Posted on: Sunday, 9 April 2006, 18:00 CDT

By Steve Pollick, The Blade, Toledo, Ohio

Apr. 9--State and federal wildlife biologists have received permission to begin culling more than 5,000 double crested cormorants from three western Lake Erie island colonies in the next three years to curb the species' destructive population growth.

"We got the go-ahead last week," said Mark Shieldcastle, project leader at the state's Crane Creek Wildlife Research Station at Magee Marsh in Ottawa County.

The U.S. Fish & Wildlife Service, which manages West Sister, and the Ohio Division of Wildlife are lead agencies in the management plan.

Culling - employing sharpshooters with noise-suppressed .22 rifles - is expected to begin this week on West Sister Island, an 82-acre outcrop nine miles off Jerusalem Township. Both a national wildlife refuge and Ohio's only federal wilderness, West Sister is the home of the most important colonial wading bird colonies on the Great Lakes.

These colonies of great blue herons, black-crowned night herons, and great, snowy, and cattle egrets are threatened by a cormorant invasion. These large, dark, fish-eating waterbirds had all but disappeared from the Great Lakes after chemical contaminants in the environment caused fatal deformities and reproductive failures.

But pollution controls primarily created a cormorant resurgence. West Sister, for example, went from zero pairs in 1990 to 3,813 in 2005. In turn the birds' high-nitrogen feces, or guano, has burned up vegetation on the island and cormorant numbers as well have crowded out other, less prolific colonials. Cormorants also strip vegetation and break down trees.

The goal is to reduce the population over the next three years to a steady 1,500 to 2,000 pairs. During the reduction, biologists will closely watch for signs of habitat improvement, cormorant reaction, and whether further measures are warranted.

Nationwide, cormorant numbers have blossomed to about two million, with nearly 70 percent living in interior areas such as Ohio.

The just-approved federal-state management program calls for integrated nonlethal and lethal controls, as deemed appropriate. The federal government in 2003 issued a broad cormorant depredation order allowing cormorant control in select areas in 24 states where science could demonstrate a problem. The species is protected by the federal Migratory Bird Treaty Act and thus great care is taken to assess cormorant impact on a case-by-case basis.

Nonlethal controls include physical exclusion, habitat modification and noise harassment. Lethal controls include shooting, oiling of eggs, nest destruction and euthanasia.

Culling by sharpshooters is being done on West Sister because it is physically impossible to reach the nests in the tree canopy and noise harassment, for example, could lead to nest failures among the threatened colonial wading bird colonies, Shieldcastle noted.

Suppressed .22s are being used also to keep down disturbance to other nesting species. A pilot project last summer demonstrated the success of this method.

"The habitat damage already done is such that a maintenance level of [1,500 to 2,000] nesting pairs is the maximum the island can sustain to conserve the Carolinian forest and sustain the other colonial wading birds," Shieldcastle explained.

Carolinian forest, marked by hackberry and Kentucky coffee tree species, is at its northermost range on the Erie islands.

On the Ontario side of the lake, complex bureaucracy and political interference from animal-rights activists has slowed the provincial response to the cormorant explosion to the point that East Sister Island and Middle Island, just north of the Ohio-Ontario border in western Lake Erie, now are all but total losses, each resembling a dead no man's land.

Ontario's Erie islands are Canada's only examples of Carolinian forest.

On Ohio's tiny, 17-acre Green Island, a state wildlife refuge, cormorant numbers alarmingly exploded from no pairs in 2003 to 857 by 2005. The goal is to eliminate cormorants there.

"The island will be destroyed in another year or two," said Shieldcastle of Green. The island harbors several endangered plant species, additional Carolinian forest, the endangered Lake Erie watersnake, and what the biologist calls a "longstanding botanical research component." It also contains a fledgling great blue heron colony and has potential for black-crowned night herons as well.

Turning Point Island, a long manmade spit of about five acres in Sandusky harbor, had 409 pairs of cormorants a year ago. Shieldcastle said the plan is to remove about 40 pairs and maintain cormorant numbers there at about 360 pairs. The lake's second-largest colony of black-crowned herons is situated there along with a fledgling snowy egret colony.

It simply has become a matter of realistically managing an out-of-control species expansion in habitat that is limited in amount and type, while maintaining survival room for other important species and habitat integrity.

Shieldcastle noted that attention also will be paid under the management initiative to fall migrations of cormorants from elsewhere. From 25,000 to 50,000 birds at a time descend on western Lake Erie in August and September. Though their presence is transitory, the damage they leave behind is not.

The biologist said that to combat migrant birds the plan is to harass them with such nonlethal methods as firing of shellcrackers.

Some migrating cormorants are to be captured and radio-tagged to learn more of their patterns and behavior.

In a related development, a one-year cooperative study to determine the diet of cormorants in western Lake Erie is getting under way. Through stomach analysis, researchers hope to establish what species of fish and other aquatic life cormorants eat. The project is being done by the U.S. Geological Survey's Lake Erie Biological Station, U.S. Department of Agriculture's Wildlife Services arm, and the USF&WS. The state wildlife division also is cooperating.

The project arose from sport angler concerns that cormorants are having an adverse impact on Lake Erie fisheries.

"This study will provide an assessment of the food eaten by cormorants in the vicinity of West Sister Island and insights into their potential impacts on Lake Erie's ecosystem," stated Mike Bur, project coordinator for the USGS lake station.

A diet study in 1997 essentially showed the cormorants, which can dive deeply and swim like a fish, mostly eat what is most available - such as gizzard shad and emerald shiners, both abundant forage species.

But since the last cormorant diet study, round gobies, an invasive forage pest-fish, have become well established. Gobies are eaten by many Lake Erie fish and are fed upon heavily by cormorants, as well.

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Copyright (c) 2006, The Blade, Toledo, Ohio

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Source: The Blade

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