Coho Salmon Near Total Year-Class Failure in Southern Range

Recent coho salmon surveys conducted in Santa Cruz and San Mateo counties failed to detect any coho salmon, suggesting that this year-class was close to a total failure for this portion of the endangered Central California Coast Coho Salmon Evolutionarily Significant Unit.

The surveys by the Fisheries Ecology Division’s Salmon Population Team were a summer-long effort to document the current distribution of coho salmon at the southern edge of the species’ historical range. Forty-six randomly selected 1-kilometer stream reaches, representing approximately 13% of the total stream kilometers believed accessible to coho salmon in the region, were surveyed with mask and snorkel for presence-absence of juvenile fish. Surveyors failed to detect coho salmon at any of the sample sites. With a single exception, other sampling in the region has failed to produce any evidence of successful reproduction during the 2006-2007 spawning year.

Coho salmon have a three-year life cycle, and it now appears that in its southern range, two of the three year-classes are lost or nearly so. This is obviously a high-risk condition.

(November 5, 2007)