Washington Department of Fish and Wildlife (WDFW) biologists recently joined in an effort to make the lower Columbia River's Rice Island less attractive to nesting, salmon-eating Caspian terns.
About 10,000 pairs of Caspian terns nest on the sandy dredge deposits of the 200-acre man-made island, which lies about 20 miles from the mouth of the Columbia River. Studies of the birds' feeding habits indicate the terns eat six to 25 million migrating salmon and steelhead smolts. That's six to 25 percent of the smolts that reach the estuary, and three to 12 percent of the smolts produced throughout the Columbia River Basin. The fish are from Columbia and Snake river runs, some of which are listed as threatened or endangered.
Last week WDFW biologists and local volunteers helped National Marine Fisheries Service and U.S. Army Corps of Engineers workers erect hundreds of rows of plastic mesh fences across seven acres of Rice Island to discourage terns from nesting. WDFW Wildlife Biologist Fred Dobler of Vancouver explained that terns like open, sandy islands for nesting where they can see each other and the water. The fences, which obstruct the birds' view, may reduce their sense of security and ultimately make the area less attractive for nesting.
The idea is to entice most of them to move 17 miles downstream to East Sand Island, a natural island in the Columbia River. Because of its closer proximity to the ocean, the diet of fish-eating birds there includes other species, such as sculpin and shiner perch, and far fewer salmonid smolts. The Corps of Engineers, with the help of the U.S. Marines, has made East Sand Island more attractive to terns by depositing and smoothing sand dredged from the river bottom. Tern decoys and tern mating call recordings also are encouraging terns to nest on East Sand Island.
"We should know if these efforts are effective by May when the terns will be laying eggs," Dobler said. Some terns already were starting mating rituals on Rice Island when work crews started the fence construction last week, he said, but some terns were also checking out East Sand Island.
Dobler and other WDFW officials noted that tern relocation is only a small part of recovery efforts for declining salmon and steelhead in the Columbia and Snake river systems. Fish passage improvements, spawning stream restoration, harvest restrictions, and hatchery operations changes all are part of the solution.