Long-term monitoring of coho salmon and steelhead trout during freshwater life stages in coastal Marin County: 2009 annual report

Reichmuth, Michael; Carlisle, Sarah; Dedrick, Allison; Rodoni, Angela

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 the complex life history of the coho salmon. Coho salmon have a three-year life-cycle in which they spend the first year of life in their natal stream followed by nearly two years in the ocean before returning to 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 that was monitored by NPS in 1997-1998 as one generation returned to spawn in the winter and the next hatched and emerged in spring and were surveyed as juveniles during the summer. These fish were surveyed again when they left the creeks as smolts in 1999 and for a third time as spawning adults in the winter of 2000-2001. Succeeding generations of cohort 1 hatched in 2001, 2004, and 2007. Cohort 2 are those fish that hatched in 1999, 2002, 2005, and 2008, 2 and cohort 3 fish hatched in 2000, 2003, 2006, and 2009. This report presents a summary of monitoring results for the 2008-2009 spawner season, 2009 smolt trapping season, and 2009 summer juvenile surveys. Adult coho escapement surveys for 2008-2009 revealed a sharp decline in the number of cohort 3 adults returning to spawn compared to the previous return of cohort 3 in 2005-2006. During the winter of 2008-2009, a major decline of cohort 3 was observed on Olema Creek with no coho spawning detected. This is the first non-detection on record for the Olema Creek coho population. Redwood Creek mainstem had an 83% decline in total coho redd production from the previous generation of cohort 3. No coho spawning activity was observed on Pine Gulch Creek. Based on juvenile coho population estimates made during the summer of 2006 and coho smolt production estimates calculated during the spring of 2007, the adult coho escapement of cohort 3 was lower than expected on Pine Gulch Creek. On both Pine Gulch and Olema Creeks, adult steelhead observations were also low with no steelhead redds observed on Pine Gulch Creek and five redds observed on Olema Creek. A total of nine steelhead redds were observed on Redwood Creek which is comparable to observations in past years.

Long-term monitoring of coho salmon and steelhead trout during freshwater life stages in coastal Marin County: 2009 annual report

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