PORTLAND, Ore. (KOIN) — The coast is clear for the United States Army Corps of Engineers to kill nearly 10,000 cormorants that feed on salmon, and bird lovers have exhausted their legal appeals.

Culling of thousands of cormorants began this past weekend in an effort to reduce their breeding population from about 14,000 breeding pairs to 5,600 by 2018.

According to the Corps, the concentration of cormorants on East Sand Island in the mouth of the Columbia River could be the largest in the world. As cormorant numbers continue to grow, so does their need for salmon.

“As they are nesting they need to feed their young and it’s a perfect food source as the smolts migrate out toward the ocean,” Robert Winters with the Corps told KOIN 6 News.

Winters said simply scaring the birds away would not eliminate the problem, and killing them would save nearly 11 million juvenile salmon from being eaten every year.

“If you put that into context, there’s 3.8 million people living in Oregon, so that’s 2.5 times the population of Oregon,” Winters said. “It’s a significant impact.”

An environmental impact statement calls for the Corps to shoot adult birds, spray eggs with oil so they won’t hatch, and destroy nests.

The Corps hopes to keep cormorants out of the lower Columbia River. The further up the Columbia the birds go, the more dangerous they can be to salmon populations.

U.S. Army Corps of Engineers spokeswoman Diana Fredlund told KOIN 6 News the culling began a few days ago. However, the times when culling or egg oiling is done will not be disclosed, she said.

Conservation groups lost their latest appeal last week when a judge refused to stop the bird kill plan. Some conservationists say dams are to blame for killing the fish, not the cormorants. A lawsuit challenging the plan is scheduled for a court hearing this summer.

Some of the salmon are protected under federal law.