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Biologists Divert Terns' Feast on Salmon

by Jonathan Brinckman
The Oregonian, April 7, 2000

The first members of what is thought to be the world's largest colony of Caspian terns are returning to the Columbia River, intent on rearing their young on a man-made island that is parked squarely before an uncommon feast: millions of finger-sized baby salmon, swimming by to make their first entrance to the Pacific Ocean.

It's a decadent scene in which the terns, accustomed to hunting and capturing elusive prey, engorge themselves on a hatchery-spawned parade of the Northwest's signature fish, all to the horror of fish biologists and bureaucrats who are in the business of saving salmon.

Federal, state and tribal biologists are stepping in to halt the carnage on Rice Island, a 230-acre island 22 miles inland from the Pacific.

The biologists, led by the U.S. Army Corps of Engineers and the National Marine Fisheries Service, have prepared a plan to keep any terns at all from nesting on Rice Island and instead to lay eggs on East Sand Island, a smaller island on the Columbia five miles from the ocean. On East Sand Island, biologists say, it is much more difficult for the terns to carry out their poaching.

The biologists expect to succeed because they have already experienced limited success. Last year, in a pilot program, biologists persuaded 1,400 pairs of Caspian terns to relocate to East Sand Island.

But the 8,100 pairs of terns remaining on Rice Island ate about 10.9 million young salmon and steelhead, about 11 percent of the 95 million out-migrating salmon and steelhead that reached the Columbia River estuary.

About 8 percent of the young salmon and steelhead that pass Rice Island on their way to the ocean are listed as threatened or endangered under the Endangered Species Act.

"I'm pretty confident the efforts to keep the birds off Rice Island will be successful," said Ben Meyer, a biologist for the fisheries service. "The birds will be wanting to go to Rice Island pretty badly, but I think we'll be able to keep them off."

Terns that nest on East Sand Island still eat salmon, but far less. Because the foraging area of East Island terns includes the open ocean, those birds eat more anchovy, herring and other small salt-water fish. That means salmon and steelhead drop to about 44 percent of their diet from about 75 percent.

Last year, to discourage terns from nesting on Rice Island, biologists placed silhouettes of bald eagles on poles and planted hostile grasses and erected fences. Terns, which lay eggs in depressions they scrape in sand, nest on open beaches so they can keep an eye out for predators.

At the same time, biologists made East Sand attractive to nesting terns by removing vegetation from four acres of beach. To lure terns they placed tern decoys on the ground and broadcast tern calls. They used rifles to kill seagulls that ate terns eggs or chicks.

This year the tern team has added one more weapon to the arsenal: people.

Michael K. Johnson Marine of Kelso, Wash., has a $61,952 contract from the Corps to maintain a two-person crew on Rice Island to chase away terns. The crew has been instructed not to harm Caspian terns, which are federally protected by the Migratory Bird Treaty Act.

The round-the-clock teams will be on Rice Island from April 11 to July 1. They're equipped with all terrain vehicles, kites and balloons. They will sleep on a barge moored at Rice Island.

The exact strategy for scaring off birds has not been worked out, said Geoff Dorsey, a corps biologist. "It's a work in progress," he said.

Dorsey thinks the presence of humans will be keep all terns off Rice Island. As a last resort, however, up to 300 eggs may be removed and turned over to the U.S. Fish and Wildlife Service.

Officials with the agency aren't convinced that terns are a huge problem for Columbia River salmon and steelhead. First, they say that efforts to remove predators do not generally help endangered species and that restoring habitat is more effective. They also think fish that are picked off by terns may be weak or diseased.

"There is a school of thought that these terns are taking fish that would have succumbed to predators anyway," said Phil Carroll, a spokesman for the agency.

Further, said Carroll, while the size of the tern colony has increased dramatically in recent years, salmon returns have not dropped correspondingly. Still, the Fish and Wildlife Service supports the relocation plan.

"The terns may not be a big problem, but they are very visible," Carroll said. "So long as terns aren't harmed, we're happy to help."

Related Sites:

Jonathan Brinckman
Biologists Divert Terns' Feast on Salmon
The Oregonian, April 7, 2000

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