Moving terns could have impact in Eugene.

Byline: INSIDE THE OUTDOORS By Mike Stahlberg The Register-Guard

Eugene is a long way from the mouth of the Columbia River, but a U.S. Fish and Wildlife Service plan for dispersing the world's largest colony of Caspian terns could impact this area in a couple of ways.

Terns are a fish-eating bird, and forcing them to set up housekeeping somewhere other than at the mouth of the Columbia would be good for juvenile salmon and steelhead, which now must swim past 20,000 hungry terns on East Sand Island to reach the Pacific Ocean.

Some of the 3 million or so salmon and steelhead smolts gobbled up each year by terns would otherwise survive to adulthood and return to the Willamette and McKenzie rivers.

So, for local salmon and steelhead anglers, the federal agency's $2.5 million tern-relocation project is welcome news.

Less clear is whether area residents should welcome the second impact of the USFWS plan - which is to lure some of the displaced terns into nesting at Fern Ridge Lake west of Eugene. The lake is one of seven sites in Oregon, Washington and California where new nesting habitat for terns would be created.

Currently, about 70 percent of the entire western population of Caspian terns in North America nests on East Sand Island in the Columbia.

Studies show the terns eat large numbers of federally protected salmon and steelhead. Tern predation on salmonids at the mouth of the Columbia is a relatively recent development. Tern nesting on Rice Island was first documented in 1986 and grew rapidly as terns lost habitat elsewhere.

Biologists say such a large concentration of terns is bad for the birds because it makes them more vulnerable to disease, predation and nest-destroying storms.

The plan released last week foresees the elimination of four acres of tern habitat on East Sand Island and the creation of eight acres of new habitat elsewhere, including 3.5 acres in Oregon divided among three sites - Fern Ridge and two lakes in southeast Oregon.

Habitat for about 3,000 pairs of terns would be left intact on East Sand Island. The USFWS estimates 6,000 pairs would be dispersed to other sites.

Decoys and recordings could be used to lure those terns to alternate sites. Such tactics worked in 1999 and 2000, when the terns were relocated to East Sand Island from Rice Island, 15 miles further upriver.

While nesting on Rice Island, the terns' diet consisted almost entirely of juvenile salmon and steelhead. On East Sand Island, the terns found many other marine fish on which to dine, and the estimated loss of 7 million salmonids a year was reduced by more than half.

The USFWS' relocation plan should "result in a 1 percent or greater increase in the growth rates of four populations of Columbia River Basin Steelhead," Pacific Region director Dave Allen said.

"Caspian terns are long-lived birds, opportunistic and very mobile, adapting well to habitat loss and gain," Allen said. "Thus, we expect displaced terns from East Sand Island to find nesting habitat at managed alternate sites and possibly elsewhere in the region."

Terns nest closely together in dense colonies. Several thousand birds can nest on only an acre or two. Their preferred habitat is usually an island with bare sand or exposed gravel, free from predators or human disturbance, with an abundance of food nearby.

At Fern Ridge, the Corps of Engineers would build a small vegetation-free island in the Gibson Island area. Terns nesting and raising their young there from May through September each year would presumably feed mostly upon warmwater fish in the lake - carp, bluegill, crappie, bass - although there is some concern they could forage salmonids from the Willamette and McKenzie rivers.

Given the high reproduction rates of warmwater species, biologists believe there would be plenty of fish in Fern Ridge for human and avian anglers alike. In fact, they say, the fishery could actually be improved because warmwater species are often stunted due to overcrowding.

Mike Stahlberg can be reached at [e-mail].