In Central California, Coho Salmon Are On The Brink

Greg Miller, Science Magazine, January 2010

The Central California coho salmon was federally listed as endangered in 2006 and the population numbers are still dropping. The historical range of Central California coho salmon once stretched from Punta Gorda in Northern California, south to San Lorenzo River in Central California. Now many Central California coho salmon populations are extirpated or nearly extirpated in several major river basins and across most of their southern range. Northern range populations may face the same fate.

In Lagunitas Creek and its tributaries, just north of San Francisco in Marin County, once home to a thriving coho run, last year’s population surveys revealed a catastrophic decline with only 64 returning adults counted while the estimate for the entire northern range is alarmingly low, at 500 returning adults. Because this is the third year in the coho three-year life cycle, the numbers of spawning adults may be too low to produce enough offspring for species survival. “We truly are at the brink of extinction,” says Charlotte Ambrose, a Recovery Coordinator with the National Marine Fisheries Service (NMFS) in Santa Rosa, California.

The precipitous population decline is due to multiple and compounding factors: dams have blocked access to habitat, thereby reducing spawning sites and offspring, the reduced numbers of offspring then face degraded habitat conditions that further reduce their survival rate. Additionally, ocean conditions off the California coast have reduced the availability of food for the hungry smolts that do make it out of the freshwater habitat, and California’s three-year drought has impeded up-stream and down-stream migrations. There are only two ways we can help the coho: habitat restoration and capture/release programs.

Conserving and improving what’s left of the coho’s habitat is the best hope for the fish’s survival, says Ambrose. A federal species recovery plan to be released next month has identified 28 watersheds, including Lagunitas Creek, where NMFS thinks habitat restoration efforts can have an immediate impact on the coho’s survival. Unfortunately, captivity and release efforts to help coho have at best mixed success rates. “Historically our best guess is that hatcheries have overall had a detrimental effect on salmon populations…due to inbreeding,” says John Carlos Garza, a NMFS geneticist in Santa Cruz. Dwindled populations of fish have a higher rate of inbreeding which leads to lower survival rates in the wild. Habitat restoration thus remains the only real hope of survival for the beleaguered Central Coast coho salmon.

Click here for the Jan. 29 article from Science Magazine.

For additional information on the Central California Coast Coho Salmon click here for the NOAA website