Caspian terns taking too many Columbia River fish

The Wenatchee World

MOSES LAKE — The largest inland colony of Caspian terns in the West is taking a big bite out of endangered fish runs in the upper Columbia River.

Though just a fraction of the size of coastal colonies, the 900-some terns living on an island near Moses Lake are single-handedly blamed for eating more than 10 percent of the wild upper Columbia steelhead juveniles and nearly 15 percent of the hatchery steelhead young as they make their way to the ocean each spring.

So this year, federal and state agencies that have already spent billions to bring back salmon and steelhead runs are trying some new tactics to temper terns and give the federally-protected steelhead a better chance at survival.

The primary effort would reduce and eventually eliminate the number of terns nesting on Goose Island in Potholes Reservoir. If successful, it could have a greater and more immediate benefit to young salmon and steelhead than the work already done at hydroelectric dams to make it easier for fish to get through them, said Tim Fleegler, project manager for the U.S. Army Corps of Engineers.

“We’re forecasting that the benefit will be substantial, particularly for steelhead,” he said.

The project got underway this year with the stringing ropes and flags across parts of the 5-acre island to make the island less attractive for the bird to nest. In the coming years, that project could be expanded to include removing eggs from nests, placing large rocks on the ground to prohibit nesting, and building habitat for the birds elsewhere. The birds are protected by the Migratory Bird Treaty Act, so the agencies have no plans to kill them outright.

In a related action, a series of manmade ponds that lie between the tern colony and the Columbia River has been stocked with non-native fish species in an attempt to entice the hungry birds to feast closer to home.

The problem

Caspian terns are a relatively new threat for juvenile steelhead and salmon making their way through the placid middle stretches of the Columbia River from rivers in Chelan and Okanogan counties to the ocean.

Migrating fish have long had to contend with dams, irrigation intakes and other predatory fish and birds. Government agencies have been working for decades to improve fish passage through dams, screen irrigation intakes, control pikeminnow populations, and chase birds away from the tailrace of dams.

Caspian terns have been chowing on fish in the estuary where the mighty river dumps into the ocean for years. But they first nested on Goose Island in 2004. The population has grown to nearly 500 nesting pairs over the last decade.

Based on the numbers of fish counted at Columbia River dams above and below the tern colony, and the numbers of fish tags recovered from the nesting site, agencies estimate that the single colony of terns is eating as many as 130,000 juvenile steelhead and salmon every year.

Studies have shown that the inland colony has a significantly higher per-capital impact on the salmon and steelhead populations than the much larger tern colony at the mouth of the Columbia River, which has a greater variety of fish to feed on.

Salmon and steelhead make up 85 percent of the Goose Island terns’ diet, compared to 35 percent of the estuary terns’ diet, according to an Oregon State University study of the birds.

A federal government report on the Caspian tern project states that the Goose Island and Crescent Island terns are one of the greatest threats to the survival of juvenile steelhead passing through the reservoirs or Priest Rapids and Wanapum dams and the Hanford Reach.

For reasons that biologists can’t fully explain, the Goose Island terns routinely fly 50-plus miles roundtrip to pluck fish out of the Columbia River rather the dining in Potholes Reservoir or other closer waters.

The federal plan

In 2008, NOAA Fisheries issued a biological opinion that guides how federal agencies manage threats to federally protected fish runs in the Columbia River basin. In part, the document mandates the U.S. Army Corps of Engineers and federal Bureau of Reclamation to deal with avian predation on fish in the river.

The two agencies and Bonneville Power Administration jointly adopted an avian management plan that got underway this year with the project at Goose Island and at another island in the Columbia River near Walla Walla. Both islands are manmade, with Goose Island being created by construction of the Columbia Basin Project’s O’Sullivan Dam.

The agencies agreed that the biggest potential benefit to fish would be controlling the Caspian tern populations on the two islands.

Studies by the agencies and by OSU researchers have shown that the terns have a far greater impact on fish that other birds, including gulls, cormorants and pelicans.

The Army Corps of Engineers is using a similar technique — ropes and flags — to reduce the size of the world’s largest Caspian tern colony at the mouth of the Columbia River. On Goose Island, some 22,500 feet of rope and 27,000 feet of flags have strung with the goal of eventually driving all of the terns away.

The federal agency has also identified 10 nearby islands that are at risk of becoming new tern colonies. So actions are being taken there to keep that from happening.

Fleegler said the Corps would like the local terns to move on to other colonies up and down the West coast. But he said the area could support a much smaller colony, closer to 50 pairs, without having a great impact on fish. So the agency may develop new habitat for the birds in the future.

The state’s plan

As federal agencies work to reduce the numbers of Caspians terns in the area, the state Department of Fish and Wildlife has devised a pilot project to create an alternative food source for the birds.

The agency manages a group of nine ponds that are fed by the Frenchman Hills Wasteway, which funnels overflow water back into the Columbia Basin Project. The ponds are controlled by a series of small dams.

Last year, several hundred sunfish were released into the ponds, which were already teeming with carp, perch, trout and other native fish. The water is usually lowered in the summer, driving many of the fish back out into the Wasteway. But the state agency kept the water high in the ponds and encouraged the fish to flourish.

Starting this spring, the agency began drawing down the levels of the ponds to make the fish more visible and easier for the terns to catch. The site is just five miles from the Goose Island colony.

The fish-filled ponds have created a birders dream, attracting not only terns but pelicans, egrets, cormorants, blue herons, black-crested night herons, and American avocet.

“We’re attracting birds without really spending any money,” said Matt Monda, fish and wildlife program manager for the agency in Ephrata.

“We’re basically putting fish in a shallow pond to see if birds will come to eat them,” he said. “If it’s viable, we could create more sites like this.”

So far, he said, it seems to be working. Terns have been feeding in great numbers at the lakes.

If the state and federal projects do what they intend, the result should be bigger steelhead counts farther down the Columbia River as early as this year.

“Salmonids are such a focus for these birds, that the benefits should be immediate,” Fleegler said. “This seems like a really good way to have a large benefit for a relatively small investment.”