Summer 2017 Juvenile Coho & Steelhead Monitoring Summary

Thank you to all of the volunteers who participated in the 2017 Summer Juvenile Salmonid Monitoring Surveys on Pine Gulch, Redwood, and Olema Creeks. Through your dedication and flexibility, all of this year’s juvenile coho and steelhead monitoring was completed successfully.

Monitoring Season Notes

Preliminary results from our juvenile coho salmon basinwide surveys indicate a decrease in numbers on Olema Creek and an increase on Redwood Creek when compared to the previous generation. One potential explanation for Olema Creek’s low success rate is that late winter storms may have scoured coho redds thereby increasing mortality of recently emerged fry. Another possibility is that spawning increased in tributary habitat which then dried up or became disconnected during the summer. In contrast, the juvenile population increase observed in Redwood Creek is likely due to the release of adult coho into the stream during the winter of 2016-2017. For an eight consecutive year, our surveys found no coho juveniles in Pine Gulch Creek.

Up Next!

The juvenile coho monitoring season has come to a close and the monitoring team is now gearing up for adult coho spawner surveys. Surveys will begin in late November and will generally be conducted following major storm events through the middle of February. Spawner surveys conducted by the National Park Service will provide a census of adult coho spawning in West Marin.

The Coho and Steelhead Monitoring Program will perform downstream migrant trapping in the spring of 2018 to evaluate the overwintering success of the juvenile coho salmon seen in Olema and Redwood Creeks over the summer.

Olema Creek

Survey teams counted a total of 69 juvenile coho during summer basinwide surveys on Olema Creek, and captured another 19 during electrofishing along fixed index reaches. These totals contributed to a preliminary 2017 basinwide population estimate of 404 coho, with a 95% confidence interval ranging from 217 to 591. That estimate is lower than the 1,034 fish estimated to be in the Olema Creek basin in 2014, the last time we observed this generation, but within the 2014 95% confidence interval [185; 1,883]. Teams observed juvenile coho throughout the 13 km stretch surveyed. Biologists implanted a total of 25 juvenile coho with PIT (passive integrated transponder) tags to allow detailed tracking of those individuals throughout their lives. This allows us to capture data on growth between life stages, timing of migration, and survival.

Redwood Creek

Teams observed a total of 272 juvenile coho during basinwide surveys on Redwood Creek, and captured an additional 58 juveniles during index reach electrofishing. The 2017 preliminary population estimate of 850 coho, 95% confidence interval [567; 1,133], is higher than the 2014 estimate of 51 coho, 95% confidence interval [9; 93]. Although survey crews saw juvenile coho throughout the mainstem of Redwood Creek, the highest concentration occurred between the confluence with Kent Creek and Bridge 1 in Muir Woods. Crews also observed higher concentrations of juvenile coho in pools near Bootjack Spur above Bridge 4. These higher concentration this high in the watershed are likely due to the above-average rainfall during the winter. Juvenile coho were observed in the Fern Creek tributary for the first time since 2013. Biologists PIT tagged a total of 64 fish during electrofishing surveys.

This year, biologists collected tissue samples from juvenile coho on Redwood Creek to determine genetic diversity and fish parentage, which help us understand adult breeding success. Small samples are clipped from the caudal fin, placed on filter paper, and sent to a NOAA laboratory for analysis.

© Martha Ture

Due to the low number of juvenile coho remaining in Redwood Creek, the California Department of Fish and Wildlife and several partner organizations collected juvenile coho during the summer months of 2014 through 2016. They reared these fish to adulthood in a conservation hatchery located at Warm Springs Dam in Sonoma County. Last winter (2016-2017) was the first official release of fish back into Redwood Creek. This summer, biologists collected tissue samples from juvenile coho and sent them to the NOAA Fisheries laboratory on UC-Santa Cruz’s Coastal Science Campus for genetic analysis to determine parentage. Such data will inform coho recovery efforts and help us evaluate the success of the adult coho release.

Pine Gulch Creek

Summer survey teams observed no coho during basinwide or index reach surveys on Pine Gulch. This corresponds with the lack of coho spawning observed during the 2016-2017 winter.

Fish Size

Based on preliminary calculations, the average fork length of coho juveniles captured on Olema Creek during the summer of 2017 was 78 mm, higher than the combined average of 71 mm from previous summers. The 2017 average fork length of coho juveniles on Redwood Creek was 70 mm, which is slightly smaller than the combined average of 73mm from prior years.

Steelhead Trout

During 2017 summer monitoring, we also captured and measured juvenile steelhead trout. On Olema Creek, the basinwide total catch of steelhead YOY (young of the year – less than one year in age) was two times the average catch, while the number of steelhead 1+ (older than one year in age) was half of the average total catch from previous years. On Redwood Creek, both the steelhead YOY and 1+ basinwide catch was the highest on record (470 and 243 respectively). The steelhead YOY basinwide catch for Pine Gulch Creek was higher than average, while the 1+ steelhead catch total was the second lowest on record.

Average fork length for YOY steelhead on Olema and Redwood Creeks was similar to the 2009-2016 combined average. Average fork length for YOY on Pine Gulch Creek was smaller than the combined historical average. Steelhead 1+ average fork length for Olema and Pine Gulch Creeks was higher than the combined average for previous years, while the average 1+ fork length on Redwood Creek was lower.

For More Information

Email Michael Reichmuth or call him at 415-464-5191.

The National Park Service shall not be held liable for improper or incorrect use of the data described and/or contained herein. These data and related graphics (if available) are not legal documents and are not intended to be used as such. The information contained in these data is dynamic and may change over time. The National Park Service gives no warranty, expressed or implied, as to the accuracy, reliability, or completeness of these data.