Long-term monitoring of coho salmon and steelhead trout during freshwater life stages in coastal Marin County: 2008 annual report

Reichmuth, Michael; Carlisle, Sarah; Dedrick, Allison; Brown, Christopher; Ketcham, Brannon

The San Francisco Bay Area Network (SFAN) monitors populations of coho salmon (Oncorhynchus kisutch) and steelhead trout (O. mykiss) in watersheds at Point Reyes National Seashore, Golden Gate National Recreation Area, and Muir Woods National Monument. The watersheds, including Olema Creek, Redwood Creek, and Pine Gulch Creek, represent the majority of streams supporting salmonids in Marin County, California, and support the southernmost stable populations of coho salmon on the Pacific Coast. The National Park Service SFAN Inventory and Monitoring Program and California Department of Fish and Wildlife have supported monitoring of multiple coho salmon life stages in coastal Marin County watersheds since 1998. Monitoring includes: • adult escapement surveys, which document the number of adult salmonids that successfully “escape” ocean fisheries and return to their natal streams to spawn, as well as the number of redds (gravel nests where salmonids lay their eggs) created; and • outmigrant smolt trapping, where smolts (at least year-old juvenile salmonids that have undergone changes to cope with a marine environment) are captured, measured and counted as they make their way towards the ocean; and • basinwide juvenile coho surveys and summer index reach monitoring which seek to quantify the number of juvenile salmonids present in the watersheds during the summer months. Monitoring of multiple life stages presents a more accurate picture of the coho population than monitoring only a single stage, especially given coho’s complex life history. Coho salmon have a three-year life-cycle in which they spend their first year of life in their natal stream followed by nearly two years in the ocean before returning their natal stream to spawn. Since generations of related fish reproduce every third year, the coho population is divided into three distinct year classes, or cohorts. Cohorts may be labeled 1, 2, and 3. Cohort 1 was the first to be monitored by NPS in 1997-1998 as one generation returned to spawn in the winter and the next hatched in spring, 1998. These fish were surveyed again when they left the creeks as smolts in 1999 and when they returned as adults in the winter of 2000-2001. Succeeding generations of cohort 1 hatched in 2001, 2004, and 2007. Cohort 2 fish are those that hatched in 1999, 2002, 2005, and 2008, and cohort 3 fish hatched in 2000, 2003, and 2006. This report presents a summary of monitoring results for the 2007-2008 season. The adults and juveniles monitored belong to different generations of cohort 2, while the year-old outmigrating smolts belong to cohort 1.

Long-term monitoring of coho salmon and steelhead trout during freshwater life stages in coastal Marin County: 2008 annual report

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