Spring Chinook Salmon swim from the Pacific ocean to Bonneville Dam to spawn. Before reaching the end of this 145 mile journey many of them disappear. This is according to research by NOAA Fisheries. California and Steller sea lions appear to dining on them says the Northwest Power and Conservation Council at www.nwcouncil.org
Steller Sea Lion males can grow to over 2,000 pounds and 10 feet in length. The sea lion habitat ranges from the subarctic to the tropics in both hemispheres with the exception of the north Atlantic.
Since 2010 NOAA researchers have been watching the annual spring run of Chinook. They have marked and released thousands of fish and tracked their progress up the Columbia River to their spawning grounds. Their destinations are either the Snake River and its tributaries in Idaho or the northern tributaries of the Columbia in north central Washington.
It is reported that the mortality rate has been increasing since 2010. Total mortality from 2010 to 2013 was about 30 percent. Approximately half of those disappeared because of harvest or handling. 24% of the chinook disappeared between river miles 28 and 145. The estimate for 2017 is 24%. Though it is a decline it means that nearly a quarter of the fish did not reach Bonneville Dam to be counted.
The warm California waters appeared to drive more sea lions north up the coast to the Columbia where they feasted on the annual smelt run which peaked in the years 2014 and 2015. Then they hung around for dessert as the annual Chinook arrived.
Speaking of smelt runs, this 85 year old writer was born, raised and lived most of her life on the North fork of the Lewis River at Woodland, Washington. One late winter she spotted some heads bobbing up and down out of the water. Lo and behold they were sea lions. Never before had she seen sea lions in the Lewis River.
Dr. Michelle Wargo-Rub, who is leading the research by NOAA, said she believes that the sea lion is responsible for the “unexplained mortality” as commercial and sport fishing and disease could not be responsible for such a large loss.
At the 28 mile mark near Tongue :Point spring Chinook are caught and tagged, then released back into the river. Sea Lions are also tagged in Astoria in order to trace their movements. Most of the sea lions stay in the area, but a few swim all the way to Bonneville where much of their dining takes place.