CHINOOK, Wash. (CN) - Heavy fog covered the dark waters of the Columbia River where it empties into the Pacific Ocean. Brown pelicans wound through the fog while a huge formation of double-crested cormorants glided and dipped. And the staccato bursts of shotguns echoed over the water.
"I don't know how they can see what they're shooting in this fog," biologist Deborah Jaques said as she piloted a Boston whaler through the rolling water.
The shooting came from government-hired gunmen, charged with killing about 11,000 protected double-crested cormorants over four years at the species' largest North American breeding colony.
A handful of government agencies hatched the plan to reduce the population of double-crested cormorants on a nearby island by nearly two-thirds, a controversial measure intended to reduce the birds' predation of endangered steelhead salmon.
As of Oct. 1, the government has killed 1,707 adults and prevented eggs from hatching in 5,089 nests, according to a report on the U.S. Army Corps of Engineers website.
Double-crested cormorants, a native species protected by the Migratory Bird Act, have always nested on East Sand Island in the Columbia River Estuary. And they've always eaten young salmon. But their population has skyrocketed over the last quarter century, from 100 breeding pairs in 1989 to about 15,000 in 2013.
The birds are sleek and slender, an iridescent blue-black. They have glittering turquoise eyes, and two tufts that rise from their brows like a crown during mating season. They hunt in an unusual manner, diving into the water to swim and usually emerging with a fish in their bright blue mouths.
East Sand Island is home to 98 percent of the breeding pairs in the Columbia River Estuary, and about 40 percent of the western population of double-crested cormorants which spans breeding colonies from Canada to California and the Rocky Mountains to the Pacific Ocean.
The endangered salmon are a perfect food source for the birds, who must feed their hungry young chicks during the same months the fish pass East Sand Island on their way out to sea.
The birds have eaten 11 million young salmon each year for the last 15 years, or about 6.7 percent of the population of juvenile steelhead, according to Diana Fredlund with the U.S. Army Corps of Engineers.
"East Sand Island offers the perfect food source," Fredlund said. "It has everything they need. How they talk to one another, I don't know. But somehow word got out that this is a perfect place to raise a family. It's a wonderful place to be if you're a cormorant trying to raise your babies. There are no predators, there's plenty of nesting materials, and you don't have to look far for your food because it's swimming right by."
In 2004, the Corps tried to attract double-crested cormorants to other island nesting sites in the estuary.
Scientists successfully used decoys and recordings of bird calls to attract cormorants to Miller Sands Spit. But those efforts required constant work to keep the birds nesting there year after year.
And it turned out that the new sites actually increased the numbers of juvenile steelhead the cormorants ate because the nests were now further up river from East Sand Island, where fewer anchovies and other saltwater-loving fish meant juvenile steelhead made up a larger proportion of their diet.
That tactic was abandoned in 2008.