Coho or Silver Salmon are an anadromous fish species found on both sides of the Pacific Ocean, found from Japan and Eastern Russia throughout Alaska and as far south as Monterey Bay in California. The Southern Oregon and Northern California Coast population found in the Rogue River Basin is listed as threatened under the Endangered Species Act in the United States, one of four Evolutionary Signifigant Units that is listed. Coho prefer smaller relatively low-gradient streams for spawning, the juvenile fish will often spend their first year in small side channels, backwaters and beaver ponds before traveling to the ocean. After their time spent at sea Coho return to our streams and rivers averaging around eight pounds, and measuring approximately two feet long.
Coho are very sensitive to pollutants, more so than other salmonids. Amounts of copper, zinc or cadmium in the water has been documented to affect the Coho’s olfactory sense, impairing it’s ability to return upstream to spawn, or being lethal to the salmon in higher concentrations. Non-point source pollution from stormwater in particular seems to be particularly lethal, with dieoff rates in urban streams getting as high as 90% when they are exposed to urban stormwater.
In addition to their sensitivity to pollutants, like all salmonids and many trout species Coho are affected in many ways by dams, habitat destruction, mining, agriculture, logging, water diversion, urbanization and climate change. Because of their listed status under the Endangered Species Act, Coho habitat is one of the main focuses of restoration efforts in the Rogue Basin.
Coho Salmon Distribution in the Rogue River Basin
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