Last updated: November 13, 2020
Article
Summer 2020 Juvenile Coho & Steelhead Monitoring Summary
(Provided data are provisional and are subject to change*)
Thank you to all who have supported our program throughout the years. Special thanks to the Latino Heritage Internship Program and Point Reyes National Seashore Association who made the completion of our 2020 Summer Juvenile Salmonid Monitoring Surveys on Redwood and Olema Creeks possible.
Monitoring Season Notes
Results from our juvenile coho salmon basinwide surveys indicate a slight increase for the Olema Creek population and decrease for Redwood Creek when compared to the previous generation. Juvenile estimates were lower than expected for Redwood Creek and slightly higher than expected for Olema Creek given the number of redds observed during the winter. We anticipated a small juvenile population in both streams given the poor spawner returns last winter. The current juvenile coho populations in both creeks are critically low. There is concern that the continuing drought conditions will further impact the coho populations as water levels remain low and potential water quality issues arise.
We were unable to perform our typical electrofishing surveys this year due to COVID-19 mitigation measures. Instead, we increased our snorkel survey sampling efforts in Redwood and Olema Creeks and seined a subset of pools snorkeled to acquire fish biotic information and PIT (passive integrated transponder) tag juvenile coho. However, due to those increased efforts combined with reduced program funding, we were unable to survey Pine Gulch Creek for the first time since the monitoring program’s inception.
Going on Now!
The summer juvenile coho monitoring season has come to a close, and the team is now gearing up for adult coho spawner surveys. Surveys will begin in late November with the onset of winter rains and continue into February. These surveys provide a census of adult coho returning to spawn in their natal west Marin streams.
NPS / Jessica Weinberg McClosky
NPS / Michael Reichmuth
If additional funding becomes available, the Coho and Steelhead Monitoring Program will perform downstream migrant trapping in the spring of 2021. Trapping migrating smolts will allow us to evaluate the overwintering success of this summer’s populations of juvenile coho salmon in Olema and Redwood Creeks.
Olema Creek
Survey teams counted a total of 110 juvenile coho during summer basinwide surveys on Olema Creek. These totals contributed to a preliminary 2020 basinwide population estimate of approximately 500 coho (official estimate will be generated once data is verified). This estimate is only slightly higher than the estimate calculated the last time we observed this generation during the summer of 2017, but within the 95% confidence interval (CI) for the estimate of 400, 95% CI [181; 619] (Figure 1). Teams observed juvenile coho in 9.3 km of the 13.0 km of surveyed stream. During seining operations, we implanted eight juvenile coho with PIT tags to allow detailed tracking of those individuals throughout their lives. Tagging allows us to capture data on growth between life stages, timing of migration, and survival.
Redwood Creek
Teams observed a total of 25 juvenile coho during basinwide surveys on Redwood Creek. The preliminary 2020 population estimate of approximately 100 coho, (official estimate will be generated once data is verified), is lower than the 2017 estimate of 873, 95% confidence interval [606; 1,140] (Figure 2). Survey crews recorded juvenile coho primarily within a 1.2 km section of stream in Muir Woods with only a few coho observed outside of this reach. In total crews surveyed 7.8 km of the mainstem of Redwood Creek and 0.8 km of Fern Creek, one of Redwood Creek’s largest tributaries. The crew PIT tagged a total of three coho during seining surveys.
Preliminary Fish Size Summary
The average fork length of coho juveniles captured on Olema Creek during the summer of 2020 was 74 mm, slightly longer than the combined average of 71 mm from previous summers. The 2020 average fork length of coho juveniles on Redwood Creek was 71 mm, which is smaller than the combined average of 73mm from prior years.
Preliminary Steelhead Trout Summary
During the 2020 summer monitoring season, we also captured and measured juvenile steelhead trout. On Redwood Creek, 224 steelhead YOY (young of the year – less than one year in age) were captured during summer seining which is higher than the average catch of 198 from previous years. The steelhead YOY basinwide catch for Olema Creek was 113 which is much lower than the running average of 307. For both streams, the basinwide total catch of steelhead 1+ (older than one year in age) was lower than the average catch from previous years. It is likely the change in capture method from electrofishing to seining resulted in fewer captures of 1+ steelhead.The average fork length of 59 mm for steelhead YOY captured in Redwood Creek was smaller than the 2009-2019 combined average of 66 mm. The average fork length of 67 mm for steelhead YOY in Olema Creek was similar to the 2009-2019 combined average. The use of seining during 2020 summer monitoring activities likely resulted in the capture of smaller fish when compared to electrofishing. This was anticipated, as electrofishing is biased towards the capture of larger fish. Fish with a larger surface area have a higher body voltage and are easier to capture via electrofishing.
*For More Information...
...about our program or regarding how to acquire certified data:
- Email Michael Reichmuth, or call him at 415-464-5191
- Visit the San Francisco Bay Area Network's Salmonid Monitoring webpage
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.
