Article published May 22, 2005
Explosive growth of cormorants in lake is a problem
The explosive growth of populations of double-crested cormorants in western Lake Erie has become a winged black plague, to the point where state and federal wildlife managers are maneuvering to take action.
These large, black fish-eating waterbirds have all but destroyed all the vegetation of Middle Sister, East Sister, and Middle islands on the Ontario side of the western basin, and their booming population on West Sister Island in Ohio waters threatens the most important colonial wading bird colony on the Great Lakes.
Experimental culling of up to 500 cormorants is under way this year with an eye toward an all-out control program later.
"It would be irresponsible for us as an agency not to react to the damage on those islands," said Mark Shieldcastle, head of the state's Crane Creek Wildlife Research Station in Ottawa County.
A survey on West Sister last year showed some 3,700 nesting pairs of cormorants, a quantum leap from an already overabundant 2,600 pairs in 2003. This year's census is not complete.
Compare that to just 185 pairs in 1991, when cormorants first reappeared after being gone for almost a century. Their populations all but disappeared from the Great Lakes because of chemical contaminant pollution, which interfered with their reproduction. On the 17-acre Green Island, a state wildlife area, 20 pairs a year ago has blossomed to 600 pairs this year. Turning Point Island at Sandusky Harbor has another several hundred pairs, and Mercer State Wildlife Area in Mercer County has 50 pair.
This spring and summer the Ohio Division of Wildlife, in cooperation with the U.S. Fish & Wildlife Service, has begun a three-year study to cull 500 cormorants from West Sister under a USF&WS collecting permit for study the recovery rate of vegetation in cormorant-free plots.Two years ago state wildlife agencies were given the authority by the federal government to control cormorant populations where evidence of damage could be scientifically established. But the U.S. Department of Agriculture has not yet completed an environmental assessment that would clear the way to issue a control or depredation order. Shieldcastle expects the assessment to be done by the fall.
"We really need that to issue a depredation order." The goal is to allow no more than 3,000 nesting pairs of cormorants at three colonies - West Sister and Turning Point on the lake, and at Mercer wildlife area. West Sister's cormorant colony alone already vastly outnumbers the projected statewide goal.
The plan is to take up to 10 percent of the birds from each colony, which would be allowed without additional review under a favorable USDA assessment, "and more if we can justify it."
West Sister is the nesting home to about 40 percent of the colonial wading birds in the Great Lakes, including rookeries for great blue herons, great egrets, black-crowned night herons, and snow egrets. All are threatened by the cormorant explosion.
"We will definitely be using that depredation permit next year," Shieldcastle said. The Ohio Division of Wildlife ultimately wants to keep tiny Green Island cormorant-free.
In addition, the western basin is threatened further by transient or migratory cormorants. "Western Lake Erie is becoming a major staging area between August and October for some unidentified populations," Shieldcastle said, noting that the migrants may number anywhere from 25,000 to 100,000 and may originate elsewhere around the Great Lakes and even from the Prairies.
Many of these transient birds sit on the edges of the islands. Their feces, or guano, is nitrogen rich and virtually burns up vegetation chemically and otherwise covers and chokes it.
Working with the USF&WS, the state wildlife division plans to initiate a hazing project at West Sister to discourage transient birds, after a study confirms suspicions.
Rocket-propelled nets initially would be used to capture a sample of transients, and they would be equipped with radio "backpacks" to establish where and how they move and how long they stay.
On the fishery side of the equation, federal biologist Mike Bur plans to cull 600 cormorants next year from three of the stressed islands - East Sister and Middle in Canadian waters, and West Sister in Ohio.
Complications arose in getting the project under way this season, but Bur said he plans on starting in 2006, taking 20 birds from each of the three colonies every two weeks then studying their stomach contents.
Bur is supervisor of the Lake Erie Biological Station of the U.S. Geological Service's Great Lakes Science Center.
He said that the expanded diet study is necessary "because the dynamic of this [lake's] fish community has changed because of the gobies. We know they eat gobies."
Gobies are an invasive pest fish from overseas that have exploded in the lake.
Roger Knight, Lake Erie programs coordinator for the wildlife division, said that cormorants "absolutely are an issue throughout the Great Lakes. They have far exceeded their historical densities."
"I am concerned about sport fish stocks, like smallmouth, because of the proximity to cormorant colonies. Smallmouth are not a migratory fish species." Knight's office had requested the recent diet analysis by Bur's crews.
Nonetheless, he is all for Bur's more intensive diet study in 2006, noting the need to "plan, monitor, track, and evaluate what you're going to do." Wildlife managers are mandated by law to demonstrate the science behind their management moves, and the threat to valuable fisheries in western Lake Erie has been much more difficult to scientifically demonstrate than terrestrial damage to the islands.
"We're not about eradicating [cormorants]," Knight said," "but about managing them at levels that are not detrimental to terrestrial and aquatic organisms and habitats."
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