By the time a Columbia River salmon has grown from a small fry to an ocean-bound adolescent, it has spent months, sometimes years, in the fresh water of the largest river in the West. A biological signal prompts the youngster to leave behind its comfortable environs and head toward the salty waters of the Pacific Ocean, where it faces enormous physiological changes.
It’s tough enough for salmon to move from fresh to marine waters where they are susceptible to a host of predators. But scientists have discovered that many of those young fish don’t even make it that far. On their way to the sea, juvenile salmon must pass the world’s largest nesting colony of Caspian terns. An Oregon State University study found that the terns consumed a staggering 12 million young salmon each year—roughly 10 percent of all the Columbia River basin salmon that survived to the estuary.
To give juvenile salmon a fighting chance at survival, OSU seabird biologist Dan Roby is assisting an effort to disperse most of the large colony of terns. “Getting colonies distributed more evenly through western North America can reduce the impacts on fish—and reduce the risk of catastrophe for the birds,” Roby said.
Historically these fish-loving seabirds would fly inland to nest on sandy islands in lakes from California to Canada. As human activities destroyed their nesting grounds, they began to bunch up, until most of the Pacific population of Caspian terns were centered on tiny Rice Island in the Columbia River. Rice Island was, perhaps, the “worst possible location for the world’s largest Caspian tern colony,” said Roby. “Terns can eat large quantities of small fish. Three-fourths of their diet was juvenile salmon and steelhead. That’s not good.”
After realizing the birds’ heavy impact on juvenile salmon, a multi-agency team created new habitat at East Sand Island to lure the terns downstream to the mouth of the Columbia where they would find a wider variety of fish. The relocation worked better than anyone expected. The East Sand Island colony now consumes less than half as many young salmon and steelhead as the former Rice Island colony—an estimated 4 to 6 million juveniles per year. “But that’s still too many,” Roby said. Now the goal is to help the terns pack up and move again, dispersing most of this über-colony to multiple locations throughout the West.
For the past couple of years, Roby has worked with the Army Corps of Engineers, Bonneville Power Administration, and U.S. Fish and Wildlife Service to develop alternative nesting sites. In early 2008, engineers created a bare sand island in southern Oregon’s Crump Lake.
“The new island looked right,” Roby said, “so we set out decoys and began broadcasting recorded sounds of nesting terns. It worked remarkably well.” Five months later, more than 500 Caspian terns found their way to this inland paradise east of Lakeview, including about 430 nesting pairs. Some had leg bands indicating they had relocated from the Columbia.
The team plowed on, literally. They created an artificial island on Fern Ridge Reservoir near Eugene, a pair of islands on Summer Lake in southern Oregon, and a nearly one-acre floating island on Sheepy Lake in the Lower Klamath National Wildlife Refuge. Roby and his colleagues eagerly awaited 2010 to see how many Caspian terns would establish themselves at the new sites, and whether birds from East Sand Island would be among them.
Then nature intervened.
Drought conditions, El Nino, and a late, cold spring led to horrendous conditions for most seabirds throughout the Northwest. “The terns nested late, with little to eat. It was, perhaps, the worst nesting year since we began monitoring,” Roby said.
At Crump Lake, just a handful of terns nested, and the few chicks that hatched were quickly devoured by California gulls. The two islands in Summer Lake didn’t fare much better. Even East Sand Island, still home to the world’s largest Caspian tern colony, logged the worst nesting year in its recorded history.
“Caspian terns fare best when there is upwelling from January through March, and ocean productivity gets off to a good start,” Roby said. “Then they come into the breeding season in good shape. It’s also good to have a deep snowpack, followed by a warm spring to encourage inland sources of food. None of those things happened this year; it was something of a disaster.”
Except at the new floating island on Sheepy Lake. There, 258 pairs of Caspian terns enjoyed a higher nesting success rate than any other colony in the Pacific Northwest. In addition, two new colonies, each with about 200 nesting pairs, appeared in south-central Alaska; among them were a number of bands identifying them as Oregon birds. Roby is intrigued how they found their way north to new sites. “The birds may have some kind of ‘populational memory’ that brings them back in times of stress,” Roby speculated. “It’s an interesting question.”
Though disappointed with the 2010 nesting season, project leaders are encouraged by their ability to create new habitat and lure birds in to nest. Their success has drawn the interest of resource managers in China, where the government is in a race to save the Chinese crested tern, one of the most critically endangered bird species on Earth. The total population is estimated to be less that 50. Like their Caspian cousins, Chinese crested terns nest on islands; the few remaining birds are located on one or two small islands in the Strait of Taiwan.
Earlier this year, Roby gave a presentation in China on Caspian terns. He was immediately sought out by Chinese officials who would like to create new habitat for the crested terns. Roby soon found himself working with resource managers from China, Taiwan, and Japan. “Despite strained relationships among these countries, everyone was working together to save this endangered bird species and learn from our experiences with Caspian terns,” Roby said.
It could be that relocating terns to protect salmon will have unexpected rewards beyond the Columbia River.