Endangered Coho Salmon Recovering Somewhat
In the years immediately before 2001, less than four endangered coho salmon returned to the Russian River (Central California) and its tributaries to spawn. This year that number is an estimated 190 adults. What caused the large increase? A captive breeding program was begun in 2001 to release the offspring of adults grown in a hatchery. It is a collaboration between government agencies, private landowners and scientists. Creating such a program was necessary because coho salmon in the region are critically endangered – to the point of being nearly extinct.
Even with a captive breeding program generating many tiny salmon fry and releasing them, there is no guarantee they will survive to adulthood and return to the rivers and creeks to breed more. For example, in 2007 only one adult coho salmon that biologists tagged returned to spawn from over 6,000 juveniles they released two years before.
So what has caused such dramatic declines in wild salmon since the 1940s when they were very abundant? The answer is human development. According to the National Marine Fisheries Service, “Water storage, withdrawal, conveyance, and diversions for agriculture, flood control, domestic, and hydropower purposes have greatly reduced or eliminated historically accessible habitat and/or resulted in direct entrainment mortality of juvenile salmonids.”
Releasing juvenile salmon bred captively won’t restore wild populations unless efforts are also made to restore the natural watersheds to a state that supports them. About ninety percent of regions riverbanks and creekbanks are owned by individuals. Cooperation between all parties committed to rejuvenating the salmon is the key to their survival.
The baby coho, aka alevin, are born in the gravel beds of California creeks and grow into fry by eating aquatic insects. Eventually they grow to a point called smoltification which prepares them to make the journey from a freshwater ecosystem to the salty ocean environment. About half of their life is spent in freshwater, and half in saltwater. After about two years they return to their birthplace to spawn, and then die.
PBS in San Francisco produced a high quality video on the salmon, and how their presence in the rivers and streams of Northern California contributes to the growth of redwood forests. When they die their decomposing bodies provide nutrients to the river environments, including the sediments which become part of the life cycle for trees.
Image Credit: University of Michigan