Fisheries  Officials  Fear  Huge  Tern  Colony  Threatens  Salmon
Picture
June 25, 1998
By ANDRE STEPANKOWSKY
The (Longview, Wash.) Daily News©The Register Guard - Used with permission

ASTORIA - Delta-winged, they glide through the sea breezes that sweep up the Columbia River.

Their backs and wings are capes of gray, their breasts shields of white. Black crests give them the dashing look of Robin Hood.

Armed with long, orange beaks, they plunge into the river to spear or grab unsuspecting fish. Then they strut after mates, offering silvery catches that droop from their beaks like handlebar mustaches.

Part cavalier and part clown, these Caspian terns are one of the lower river's greatest sights - even though they represent the latest challenge to saving Columbia River salmon. They are taking as many as 12 million smolts a year and researcher's and top wildlife managers are gathering in Portland this week to figure out a way to scatter the colony, which may be the biggest in the world.

Again this spring, thousands of terns settled down after migrating from Central and South America to breed on Rice Island, a 2-mile strip of sand created nearly four decades ago by Army Corps of Engineers' dredges. And again, the birds are devouring young salmon - 5 million to 12 million of them from hatcheries and from as far upriver as Idaho, according to Oregon State University researchers.

Clustered into a few acres on the downriver side of the island, the colony looks like a white cloud settled on the beach. It numbers 9,000 to 16,000 birds.

Terns once were scattered among many island colonies across the region. In the 1980s, they began clustering at Rice Island, which was created in 1962. No one knows why it took so long for them to "discover" Rice Island or why they abandoned others, although a few islands did wash away.

But Rice Island's draw is easy to grasp: It has great habitat and a ready feast.

Located about 15 miles from the river's mouth, the island has acres of barren river sand. It's perfect nesting ground for terns, who like open sand so predators can't creep up through grass or brush.

The island also is located near a zone where salt- and fresh water mix. An estimated 100 million young salmon linger here each spring as they adjust to saltwater before heading out into the ocean. The result is a feeding frenzy.

"We need to do something about them. They're having much too large an impact," says David Craig, an OSU researcher based in Astoria.

Today, the Corps of Engineers, National Marine Fisheries Services, U.S. Fish and Wildlife Service and Oregon Department of Fish and Wildlife will meet in Portland to discuss ways to prevent the terns from using the island next spring. Among the ideas: harass them, vegetate the island or lure them to other places.

OSU researchers have had success moving terns to Miller Sands Island, about a mile upriver from Rice Island, in a small-scale experiment using tern decoys and recorded tern calls.

There is a possibility, however, that nature could solve the problem on its own. Despite being a meal ticket to a salmon banquet, the island is proving too savage a place to raise young. Out of an estimated 25,000 eggs the terns laid last year, only 500 fledglings survived. Gulls and bald eagles, attracted by the presence of so many terns, ate most eggs and chicks, Craig said.

Eagles kill and eat adult terns and larger fledglings. Gulls snatch eggs and chicks when eagles chase off the tern adults. Bigger than the terns, the gulls bully the smaller species out of 5 percent to 10 percent of their catch, Craig says.

These ongoing problems, and the gradual establishment of vegetation on Rice Island, could eventually disperse the colony.

"Once a bird nests in one spot and is successful, they tend to breed there again the following year," says Brad Bortner, chief of the migratory bird division for the U.S. Fish and Wildlife Service in Portland. But they will abandon a nest site if predators or other problems confront them, he added.

Bird biologists are as concerned as fish biologists about the tern cluster, fearing that disease or a spill disaster could wipe out most of the region's population. "We'd like to get back to a situation where they are dispersed in smaller colonies - for their own good and for the fisheries," Bortner says.

Killing the birds is illegal under international treaty. Some environmentalists suggest removing Rice Island and dumping the sand in the ocean, a proposal that would cost tens of millions of dollars.

One big question, which is under study, is how much the terns reduce the number of returning adult Salmon. The terns may just be picking off weak smolts that would have died anyway, says Dan Roby, one of the lead OSU researchers.

"So many of them have been stressed out by the trip (downstream)," Roby said. "A weak fish may be lethargic and near the surface. They are not real good at avoiding predators. There could also be so many fish in the estuary that a large portion escape. There are only go many birds and they can't be everywhere at once."

Rice Island is the only place on the river where avian predators -gulls, terns and cormorants - are wolfing down significant numbers of salmon. That surprised OSU researchers, who had theorized that the Columbia's hydroelectric reservoirs were perfect places for birds to swoop down on salmon.

The dams, though, may share some blame for the tern problem. Craig speculates: Because dams spread out, the spring runoff, salmon get washed down in a steady stream instead of in pulses. "So there's a constant supply of salmon for the terns," Craig says.

Print