Long-term monitoring of coho salmon and steelhead during freshwater life stages in coastal Marin County: 2018 annual report (revised with costs)

McNeill, Brentley; Reichmuth, Michael; Iwaki, Alex

doi:10.36967/nrr-2279705

The San Francisco Bay Area Network (SFAN) monitors populations of coho salmon (Oncorhynchus kisutch) and steelhead (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 (CDFW) 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 the number of 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. Multiple life-stage monitoring allows for a more accurate representation of the coho population, 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 to be 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, 2007, 2010, 2013, and 2016. Cohort 2 are those fish that hatched in 1999, 2002, 2005, 2008, 2011, 2014, and 2017 and cohort 3 fish hatched in 2000, 2003, 2006, 2009, 2012, 2015, and 2018. This report presents a summary of monitoring results for the 2017-2018 spawner season, 2018 smolt trapping season, and 2018 summer juvenile surveys. The adults and juveniles monitored belong to different generations of cohort 3, while the year-old outmigrating smolts belong to cohort 2. Adult coho escapement surveys on Olema Creek for 2017-2018 showed a slight increase in cohort 2 adults returning to spawn (8 redds in 2017-2018 compared to 6 redds in 2014-2015). Redwood Creek adult escapement increased significantly from 4 redds in 2014-2015 to 54 redds in 2017-2018. This substantial increase can mostly be attributed to the release of 188 adult coho on January 12, 2018 as part of the Rescue and Captive Rearing Project led by CDFW. Pine Gulch Creek had no adult coho observed for the eighth year in a row. On Olema Creek, a basinwide juvenile coho population estimate of 1,301, 95% CI [960, 1,642] was calculated. The basinwide juvenile coho population estimate for Redwood Creek was 4,475, 95% CI [3,613, 5,337]. The Olema Creek juvenile population estimate for 2018 was slightly higher than the estimate for 2015 which is the last time this cohort was observed as juveniles. Redwood Creek’s 2018 juvenile coho population estimate was almost double the 2015 estimate which, again, was mostly due to the adult coho release. No juvenile coho were observed...................

Long-term monitoring of coho salmon and steelhead during freshwater life stages in coastal Marin County: 2018 annual report (revised with costs)

Series

Other versions

Collections