The study paid for by the U.S. Army Corps of Engineers found that salmonids made up 11.7 percent of the underwater-swimming birds' diet, with juvenile and immature adult fall chinook accounting for about 3.4 percent of that.
Researchers concluded that the double-crested cormorants were eating a relatively small number of chinook while also eating nonnative fish that prey on juvenile fall chinook.
"Any action we take on these birds wouldn't have much benefit," David Trachtenberg, a fisheries biologist for the corps based at Walla Walla told the Lewiston Tribune.
The researchers killed 130 cormorants during the study and examined the contents of their stomachs.
Bass and sunfish made up 34.3 percent of the diet, juvenile shad 15 percent, minnows and carp 11.7 percent, catfish 6.3 percent, and perch 3.4 percent.
"We have been monitoring populations since 2004," said Cindy Boen, a project manager for the corps at Walla Walla. "The predation on Granite Pool is very limited. It is not cause for concern compared to some of the other (bird) colonies."
Those other bird colonies include Caspian terns. The corps is developing its Inland Avian Predation Management Plan that could lead to reductions in the size of two inland populations of the species.
One colony is nesting on Crescent Island on the Columbia River, just downstream from the mouth of the Snake River, and another is on Goose Island at Potholes Reservoir, near Othello. Officials estimate that the Goose Island terns are eating about 10 to 15 percent of the upper Columbia River steelhead populations listed as endangered. The Crescent Island tern population is believed to be consuming about 7.7 percent of the wild Snake River steelhead population.
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