Summer 2019 Juvenile Coho & Steelhead Monitoring Summary

Thank you to all of the volunteers who participated in the 2019 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 the population on both Olema Creek and Redwood Creek when compared to the previous generation. Juvenile estimates were lower than expected for both streams given the number of redds observed during the winter. One potential explanation is higher mortality during the egg incubation and early-rearing life stages. Peak spawning occurred in December of 2018, and was followed by significant rainfall and high flows in mid-late February. Though large February storms aren’t unusual, one later in the month generated a peak flow of over 2,000 cubic feet per second (cfs) in Olema Creek, which only sees flows of that magnitude approximately once every 15-20 years.

Up Next!

The summer juvenile coho monitoring and winter coho spawning seasons have come to a close, and the team is now surveying for adult steelhead. Surveys will continue through April and will generally be conducted following major storm events. These surveys provide a census of adult coho and steelhead returning to spawn in their natal west Marin streams.

When those high flows occurred, coho offspring were likely still incubating or just beginning to emerge from the gravel. At these stages, they are extremely vulnerable to being swept away by such fast-moving water. For the tenth 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 2020 to evaluate the overwintering success of this summer’s populations of juvenile coho salmon in Olema and Redwood Creeks.

Sculpin are native to our coastal watersheds. They typically live on or near the bottom of the creek and are known as ambush predators, eating mainly macroinvertebrates. However, large individuals such as this one measuring over eight inches long can easily eat unsuspecting juvenile coho.

NPS / Michael Reichmuth

Olema Creek

Survey teams counted a total of 1,402 juvenile coho during summer basinwide surveys on Olema Creek and captured another 218 during electrofishing along fixed index reaches. These totals contributed to a 2019 basinwide population estimate of 8,978 coho, 95% confidence interval [5,371; 12,585]. This estimate is lower than the 17,337, 95% confidence interval [12,527; 22,147] (Figure 1), coho juveniles estimated to be in the Olema Creek basin in 2016, the last time we observed this generation. Teams observed juvenile coho in 10.5 km of the 12.4 km of surveyed stream. Biologists implanted a total of 198 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.

Figure 1. Summer juvenile coho basinwide population estimates for Olema Creek, 2004 through 2019. Cohorts are designated by color (cohort 1 shown in yellow, cohort 2 shown in blue, cohort 3 shown in red).

Redwood Creek

Teams observed a total of 497 juvenile coho during basinwide surveys on Redwood Creek and captured an additional 110 juveniles during index reach electrofishing. The 2019 population estimate of 1,594 coho, 95% confidence interval [989; 2,199], is lower than the 2016 estimate of 2,459 but within the 95% confidence interval [1,435; 3,483] (Figure 2). Although survey crews recorded juvenile coho throughout the mainstem of Redwood Creek, the highest concentrations were downstream of Muir Woods National Monument. Crews also observed juvenile coho in pools upstream of the Bootjack Spur past 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 121 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. Fish were reared to adulthood in a conservation hatchery located at Warm Springs Dam in Sonoma County. Last winter (2018-2019) was the third and final official release of coho adults 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 release.

Figure 2. Summer juvenile coho basinwide population estimates for Redwood Creek, 2004 through 2019. Cohorts are designated by color (cohort 1 shown in yellow, cohort 2 shown in blue, cohort 3 shown in red).

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 2018-2019 winter.

Fish size summary

The average fork length of coho juveniles captured on Olema Creek during the summer of 2019 was 70 mm, slightly lower than the combined average of 71 mm from previous summers. The 2019 average fork length of coho juveniles on Redwood Creek was also 70 mm, which is smaller than the combined average of 73mm from prior years.

Steelhead trout summary

During the 2019 summer monitoring season, we also captured and measured juvenile steelhead trout. On all three creeks, the basinwide total catch of steelhead YOY (young of the year – less than one year in age) was higher than the average catch from previous years. On Redwood Creek, the steelhead YOY basinwide catch was the highest on record with 748 captured. That is significantly higher than the average catch of 198 from previous years. The steelhead YOY basinwide catch for Olema Creek was the second highest on record with 564 steelhead captured. On Pine Gulch Creek, a total of 171 steelhead YOY were captured, which is also higher than average. For all three streams, the basinwide total catch of steelhead 1+ (older than one year in age) was similar to the average catch from previous years.

The average fork length of 60 mm for YOY steelhead on Redwood Creek was smaller than the 2009-2018 combined average of 67 mm. The average fork length of 68 mm for YOY steelhead in Olema was similar to the 2009-2018 combined average. Like Redwood Creek, average fork length of YOY steelhead captured in Pine Gulch Creek (54 mm) was smaller than the 2009-2018 combined average of 60 mm. Steelhead 1+ average fork length for Redwood Creek (135 mm) and Pine Gulch Creek (138 mm) was higher than each stream’s respective combined average of 128 mm. Steelhead 1+ average fork length in Olema Creek (129 mm) was similar to the 2009-2018 combined average of 128 mm.

For More Information

• Visit the San Francisco Bay Area Network's Salmonid Monitoring webpage.
• 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.