The cormorant population on East Sand Island has exploded in recent decades, growing from 100 pairs in 1989 to about 15,000 pairs in 2013 — making it the largest breeding colony for the birds in North America, the statement said.

The cormorants, which prey on juvenile salmon protected by the Endangered Species Act (ESA), have hit the Columbia River’s salmon population, the Corps contends.

Earlier this year, the Corps published an Environmental Impact Statement and culling plan based on nearly 20 years of research of the birds’ impact on salmon. After a period of public review, the FWS gave the Corps a depredation permit to cull the birds.

In 2014, the National Oceanic and Atmospheric Administration (NOAA) issued a mandatory action to protect ESA salmon by improving fish passages at dams, cultivating their habitats, and managing predator populations, the Corps noted in its statement.

But critics and conservationists have questioned the culpability of the cormorants, and instead blamed the Columbia River’s hydroelectric dams for pushing salmon towards extinction.

To stop what they called a "slaughter," the Audubon Society of Portland filed a lawsuit in April along with four other animal and conservation organizations against the Corps, the FWS and the USDA Wildlife Services, the group said in an April 20 statement.

The suit alleges that the cormorants are merely scapegoats for the salmons' decline while the real threat is mismanagement of the federal hydropower system.

“This is not about birds versus fish,” said Bob Sallinger, conservation director of the Audubon Society of Portland. “The Corps and other federal agencies have proposed rolling back dam operations that benefit salmon while at the same time targeting thousands of cormorants."

"Blaming salmon declines on wild birds that have coexisted with salmon since time immemorial is nothing more than a diversion,” he added.