PORTLAND (AP) — Federal officials are proposing to kill half the large colony of cormorants in the Columbia River estuary because the large black seabirds eat too many young salmon and steelhead.

The proposal is the preferred action in a draft management plan released Thursday by the U.S. Army Corps of Engineers.

The colony of double-crested cormorants on East Sand Island near the mouth of the Columbia consumes about 11 million juvenile salmon per year as it migrates through the river to the Pacific Ocean. The fish are listed as endangered.

Officials say despite reductions in nesting habitat, the cormorant population has continued to thrive. It has increased from 100 breeding pairs in 1989 to about 15,000 breeding pairs today. That makes it the largest cormorant colony in western North America, representing over 40 percent of the region’s cormorant population.

The Corps has been studying the impact of avian predation on juvenile salmon in the Columbia since 1997. Officials also have looked into methods such as hazing with lights and using human presence to flush cormorants off potential nesting sites.

Now federal officials are proposing to reduce the colony to 5,600 breeding pairs by killing half of them, trying to scare off the others and taking their eggs.

The $1.5 million-a-year program, planned over four years, would arm federal trappers with silenced rifles and night-vision scopes to shoot the birds during their nesting season. They’d also cover eggs in oil to prevent them from hatching and inundate part of the island once the cormorant population reaches a target to limit nesting.

Once the target colony size is attained, the Corps also is proposing to modify the terrain of East Sand Island to inundate some nesting habitat.

The Corps passed over an alternative that would only use nonlethal methods, saying it would be less effective and push cormorants to nest elsewhere in the Columbia River estuary or in other coastal areas with endangered fish.

“That is a significant concern,” said Sondra Ruckwardt, the Army Corps’ project manager overseeing the plan. “We’re trying not to move the problem.”

Double-crested cormorants have orange faces and long necks, and are masters at diving to catch small fish. They are protected under the Migratory Bird Treaty Act and are native to the Columbia.

Federal officials also are trying to protect salmon by killing off sea lions — another protected species that has also proved too difficult to scare off with non-lethal methods.

The public has through Aug. 4 to comment on the cormorant plan.