PORTLAND, Ore. (CN) — Bird advocates tussled with the government Wednesday, claiming that the killing of thousands of native cormorants likely had little to no effect on the population of endangered salmon that return from the Pacific to spawn in the Columbia River Basin and did nothing to address the true reason for the endangered fish's decline: hydroelectric dams.
The Audubon Society of Portland led an April 2015 lawsuit against the U.S. Army Corps of Engineers, U.S. Fish and Wildlife Service and U.S. Department of Agriculture Wildlife Services. Lawyers argued their cross-motions for summary judgment before U.S. District Judge Michael H. Simon on Wednesday.
The dispute began with a biological opinion calling for the government to increase the population of adult salmon that return each year to the Columbia River and its tributaries to spawn. To comply with the opinion, the government could have chosen any danger facing salmon at any point in their lifecycle.
The Corps decided to focus on the number of young salmon that make it out to sea, reasoning that if that population increased, the number of adults that make it back would rise as well. From there, the Corps narrowed the long list of possible dangers facing juvenile salmon to one: cormorants.
East Sand Island, a 60-acre island in the fertile waters where the Columbia River empties into the Pacific Ocean, is home to the largest breeding colony of double-crested cormorants in North America.
The sleek, blue-black birds are native to the area and protected under the Migratory Bird Act. They hunt by diving into the water to swim after small fish.
In 2015, the government launched a program to kill about 11,000 double-crested cormorants over four years, reducing the population of the species' largest North American breeding colony by nearly two-thirds.
Since May 2015, the government has shot 4,740 double-crested cormorants on or near East Sand Island and poured vegetable oil on 6,181 nests to suffocate the eggs.
But bird advocates say killing all those birds may have accomplished nothing.
No one knows whether reducing the number of young fish eaten by cormorants, a natural predator that co-evolved alongside salmon, will actually affect the numbers of returning adults.
For every 100 salmon that hatch in the river and go out to sea, between one and three will return to the spot where they were born to lay their eggs. Between those two points in the salmon lifecycle, there are dozens of lethal forces that can kill them.
Even if all the young salmon in any given year survive their swim past East Sand Island in the mouth of the Columbia River, there is no way to know for sure whether the same number might end up eaten by other birds or swimming predators, chewed up in the turbines of a hydroelectric dam or dead from diseases that proliferate in warming waters.
That idea is called compensatory mortality — if you remove one predator or danger, what is the rate at which the same fish will be killed by something else? In other words, how many of the young fish that weren't eaten by cormorants will end up dead for another reason?
No one knows the answer to that question, and the Audubon says that means the Corps' plan has no firm basis in science.