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When Dams and Dredging Alter an Ecosystem, Blame It on Cormorants

By Richard King
From the Autumn 2014 issue of Living Bird magazine.
Double-breasted Cormorant by Lorcan Keating via Birdshare
Should Double-crested Cormorants be killed to protect young salmon at the mouth of the Columbia River? Photo by Lorcan Keating via Birdshare.

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If you’re looking for a dinner party debate among environmentally minded friends, I’ve got the case study for you. Start by serving wild salmon—the cultural and ecological icon of the Pacific Northwest. After the first forkfuls, explain how rising populations of seabirds living on a tiny island at the mouth of the Columbia River have pushed a hierarchy of government agencies into the position of trying to assuage the interests of fishermen, hydropower companies, salmon hatcheries, tribal representatives, and environmentalists—while at the same time representing the Endangered Species Act, the Migratory Bird Treaty Act, and attempting to balance the economics of commerce and jobs.

Here’s the dilemma: in the spring and early summer when young salmon are trying to swim out of the Columbia River and into the open Pacific, tens of thousands of Double-crested Cormorants and Caspian Terns on Oregon’s East Sand Island are fishing to feed their young. In 2012, researchers estimated that Double-crested Cormorants ate about one of every eight salmonid smolts that had survived to reach the mouth of the river. In an effort to reduce this predation, the U.S. Army Corps of Engineers has proposed shooting during the next four years at least 8,000 breeding pairs of these federally protected cormorants while they sleep on their nests at night.

While chewing on the ethical and legal ramifications of a lethal action like this, your guests might like a dash of historical background, because East Sand used to be only a shifting shoal in a highly dynamic estuary. From the 1940s through the early 1980s the War Department and the Army Corps stabilized and built up the islands with dredge spoils to clear the channel for shipping. Caspian Terns began nesting on East Sand in 1984 and the cormorants followed five years later. It’s now the biggest colony in the world for both Doublecrested Cormorants (about 14,900 pairs) and Caspian Terns (about 7,400 pairs). The Corps hopes to cap the cormorant colony at about 5,600 pairs, then flood part of the island in order to reduce cormorant nesting habitat.

“This is an enormously productive estuary in the amount of forage fish it can provide,” explains Daniel Roby, who leads seabird diet and population studies in the lower Columbia. “And because of our regular presence and monitoring, the Corps and our researchers have actually been protecting East Sand from public disturbance.”

So what do you do when federally protected birds prey on federally endangered salmon and steelhead—most of which have been hatchery raised? Roby and his team have moved some nesting terns away from the Columbia using decoys to set up new colonies, but moving cormorants has proved slower. No state or local authority has pledged to provide new safe habitat for this species. And if cormorants stay in the Columbia, officials don’t want to go around “playing whack-a-mole,” as Roby puts it, chasing cormorants from island to island to protect the young salmon.

Black, silent, and gothic with their spread-wing posture, cormorants are easy scapegoats. But Roby says: “Cormorants eat whatever fish are most available, so they’re clearly not on East Sand because they’re specializing on hatchery-raised salmonids.” The percentage of salmonids in the cormorants’ diet varies from 2 to 28 percent from year to year, averaging about 10 percent. Anchovies, flounder, sculpin, and other fish for which there is no local commercial interest make up the majority of their food here. Double-crested Cormorants are native to the Columbia, and East Sand represents more than 40 percent of the western North American population. Double-crested Cormorants will thrive near productive wild fish stocks of any species, in fresh or saltwater, in nearly any place in North America—but only if there is safe breeding habitat.

Roby sighs when he thinks about the problem. He believes a century’s worth of damming throughout the vast Columbia watershed has been the primary reason for the status of salmon today, but with the need for power, irrigation, and navigation in the West, hydropower is a fixture here. “The cormorants certainly aren’t the reason why we are where we are today with salmon,” he says. “But the dams aren’t going away. And the salmon are still endangered.” Refill the wine and discuss.


Adkins, J. Y., et al. 2014. Recent population size, trends, and limiting factors for the Double-crested Cormorant in western North America. Journal of Wildlife Management doi: 10.1002/jwmg.737.

Roby, D. D., K. Collis, et al. 2013. Research, monitoring, and evaluation of avian predation on salmonid smolts in the lower and mid-Columbia River: Final 2012 annual report. Oregon State University, Real Time Research, and U.S. Geological Survey– Oregon Cooperative Fish and Wildlife Research Unit, Corvallis, Oregon.

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