For salmon, if it’s not one thing it’s another.
In the Klamath River Basin straddling the Oregon-California border, salmon compete with onion, potato and wheat farmers for the ever-scarcer water. Dams on the river have also contributed to the decrease in the salmon population. Further north, sea lions from California(!) travel all the way up to the Columbia River to feast on the salmon returning to their spawning grounds. That’s if a few years earlier they escaped predation by cormorants as they made their way from the river to the salt water of the Pacific.
(Fun Fact: The name “cormorant” is a contraction of the Latin words corvus and marinus which taken together mean “sea raven.”)
The Astoria-Megler Bridge spans the four-mile wide Columbia River near its mouth where it empties into the Pacific Ocean. Ten-thousand double-crested cormorants have made their home on the bridge this year, a ten-fold increase over previous years. The diving birds previously nested in greater numbers seven miles away on the man-made East Sand Island. In years past, the Army Corps of Engineers has destroyed eggs and nests on the island and for a while had a campaign of shooting the birds. The success of those programs resulted in the birds relocating on and under the bridge.
Salmon passing under the bridge are easier prey for the diving predators. The fish are concentrated in a passageway that is narrower than the downstream island that is closer to the river’s mouth.
And it’s not only salmon that need fear the cormorants. Ten-times as many birds leave ten-times as much guano on the bridge. These acidic deposits eat through the paint, and re-painting, of course, is an expensive project.
