Third Consecutive Weak Year for Coho South of San Francisco

Coho salmon experience third consecutive weak year class in streams south of San Francisco Bay.

Snorkel surveys conducted this summer by the SWFSC Fisheries Ecology Division’s Salmon Population Team indicate the 2007-2008 spawning year for coho salmon was poor and that the species is nearing extinction in the southern portion of its range.

Surveys were conducted in 64 stream reaches totaling approximately 18% of the total accessible habitat in Santa Cruz and San Mateo counties from San Gregorio Creek to Aptos Creek. Most survey sites were randomly drawn, but more thorough surveys were conducted in four streams that have supported coho salmon in recent years: Gazos, Waddell, Scott, and San Vicente creeks.

Juvenile coho salmon were found in small numbers in five of the eleven watersheds surveyed: San Gregorio Creek, Waddell Creek, Scott Creek, San Vicente Creek, and Soquel Creek. In all cases, fewer than 190 individuals were observed, and numbers were particularly low in Scott and Waddell creeks, where only 4 and 34 fish were observed over distances measuring 6 and 7.5 km of stream, respectively. To our knowledge, the finding of juvenile coho salmon in Soquel Creek represents the first evidence of successful reproduction in this watershed in several decades. Conversely, the apparent absence of coho salmon in Gazos Creek is significant in that this brood lineage has been consistently observed over the past 4-5 generations (12-15 years), but now appears extinct.

Overall, the weak year class is particularly alarming since this brood cycle has historically been the strongest of the three in the coho life history. Surveys conducted in 2006 detected juvenile coho salmon only in Scott and San Vicente creeks, while no coho salmon were observed in any of the study watersheds in 2007.

(October 14, 2008)