Summer 2018 Juvenile Coho & Steelhead Monitoring Summary

Thank you to all of the volunteers who participated in the 2018 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 an increase in population on both Olema Creek and Redwood Creek when compared to the previous generation. However, both Olema and Redwood Creek juvenile estimates are lower than expected given the number of redds observed during the winter. One potential explanation is higher mortality during the early-rearing life stage. Peak spawning occurred a little late, in mid-January of 2018. The offspring from this spawning period likely emerged in mid-March. Following their emergence, coho fry need very slow moving water to feed and thrive.

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.

In early April, however, Olema and Redwood Creeks experienced the largest spring storm event on record for the area. The storm increased water velocities in both creeks and probably made it difficult for the newly emerged coho fry to survive. For the ninth consecutive year, our surveys found no coho juveniles in Pine Gulch Creek.

The Coho and Steelhead Monitoring Program will perform downstream migrant trapping in the spring of 2019 to evaluate the overwintering success of this summer’s populations of juvenile coho salmon in Olema and Redwood Creeks.

Volunteers assist with netting fish in Olema Creek as they are temporarily stunned by a backpack electrofisher. Electrofishing is used by the Coho and Steelhead Monitoring Program as a way to determine the size and relative health of the the salmonid population during the summer months.

NPS / Brentley McNeill

Olema Creek

Survey teams counted a total of 345 juvenile coho during summer basinwide surveys on Olema Creek, and captured another 57 during electrofishing along fixed index reaches. These totals contributed to a preliminary 2018 basinwide population estimate of over 1,700 coho. This estimate is higher than the 1,006 fish estimated to be in the Olema Creek basin in 2015, the last time we observed this generation, but within the 2015 95% confidence interval [226; 2,069]. Teams observed juvenile coho throughout the 13 km stretch surveyed. Biologists implanted a total of 52 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 1,153 juvenile coho during basinwide surveys on Redwood Creek, and captured an additional 178 juveniles during index reach electrofishing. The 2018 preliminary population estimate of over 4,500 coho, is higher than the 2015 estimate of 1,852 coho, 95% confidence interval [457; 3,448]. Although survey crews saw juvenile coho throughout the mainstem of Redwood Creek, the highest concentration occurred between Pacific Way Bridge and the confluence with Kent Creek. Crews also observed juvenile coho in pools upstream of the Bootjack Spur above Bridge 4. This suggests that adult coho had full access to available spawning habitat within the Redwood Creek watershed and fully utilized the watershed. Biologists PIT tagged a total of 149 fish during electrofishing surveys.

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 (2017-2018) was the second 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 2017-2018 winter.

Fish Size

Based on preliminary calculations, the average fork length of coho juveniles captured on Olema Creek during the summer of 2018 was 72 mm, slightly higher than the combined average of 71 mm from previous summers. The 2018 average fork length of coho juveniles on Redwood Creek was 68 mm, which is smaller than the combined average of 73mm from prior years.

Steelhead Trout

During 2018 summer monitoring, we also captured and measured juvenile steelhead trout. On Olema Creek, the basinwide total catch of both steelhead YOY (young of the year – less than one year in age) and 1+ (older than one year in age) were similar to the average catch from previous years. On Redwood Creek, the steelhead 1+ basinwide catch was the second highest on record with 127 captured. The steelhead YOY season total of 98 was average. The steelhead YOY basinwide catch for Pine Gulch Creek was lower than average for 1+ steelhead while the catch total for YOY steelhead was the lowest on record.

Average fork length for YOY steelhead on Redwood Creek was larger than the 2009-2017 combined average. Average fork length for YOY steelhead in Olema and Pine Gulch Creeks was similar to the 2009-2017 combined average. Steelhead 1+ average fork length for Redwood Creek was lower than average. Steelhead 1+ average fork length was similar to the 2009-2017 combined average in both Pine Gulch and Olema Creeks.

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.