Measuring the health of Mt. Tam
Maintaining a healthy, vibrant and diverse Mt. Tam begins with understanding how key ecological resources are faring, and how we can better care for this iconic and beloved place.
One Tam partners and Bay Area scientists have come together to try to answer the question: How healthy are Mt. Tam's natural resources?
Coho Salmon in Redwood Creek
Why Was This Indicator Chosen?
Endangered coho salmon (Oncorhynchus kisutch) in Redwood Creek are good indicators of riparian habitat and hydrological conditions as well as ocean health, and provide marine-derived nutrients for aquatic and riparian communities. Decades of monitoring data covering all life stages make it possible to assess the condition and trend of coho salmon on Mt. Tam with a fairly high level of confidence.
What is Healthy?
The desired conditions for Redwood Creek coho salmon populations are described in numerical targets for each life stage, as well as the critical habitat conditions that support those life stages. The National Marine Fisheries Service (NMFS) recovery plan for this species (2012) lists specific goals for the number of adult spawners and redds (nests), juveniles, and smolts (young fish migrating out to sea), and the amount of woody debris in the stream.
What Are the Biggest Threats?
- Historic hydrological changes and habitat loss that have affected anadromous fish migration, increased sedimentation, and reduced the number of pools and other critical habitats
- Current hydrological changes and habitat loss including water withdrawals, drought, channel incision, and a loss of downstream floodplain connectivity
- Ocean-related factors such as over-harvesting of salmonids as well as their prey (e.g., sardines) and changes to ocean food webs related to climate change
- Potential invasive aquatic species including exotic mollusks such as New Zealand mud snail (Potamopyrgus antipodarum) and the spread of invasive Japanese knotweed (Fallopia japonica)
- The effects of climate change such as higher water temperatures, longer droughts, more intense rainfall, and disruptions in the ocean food web
What is The Current Condition?
The overall condition of Redwood Creek’s coho salmon is Poor. Two of three year classes have been hovering near extirpation since 2008. Numbers of adults and redds are only at approximately 12% of the NMFS recovery goal, and smolts are at about 9%. The amount of woody debris is also below recovery goals.
What is the Current Trend?
Overall, this species is Declining. Over the last nine years (three generations) two of three year classes have remained at dangerously low levels in Redwood Creek, while the third year class recently declined. Wood loading is improving however, and the numbers of pools per mile has not changed.
How Sure Are We?
We have Moderate confidence in this assessment based on the amount and quality of data we have on coho life stages, but there is some uncertainty around juvenile and smolt estimates.
What is This Assessment Based On?
- NMFS Federal Register documents (NMFS 2012, 2015)
- National Park Service inventory and annual monitoring (Carlisle et al., 2016)
- Redwood Creek Watershed Assessment (Stillwater Sciences, 2011)
What Don’t We Know?
Key information gaps include:
- The timing and magnitude of salmonid migration between streams using Passive Integrated Transponder (PIT) tag technology would provide valuable information on habitat needs during multiple life stages
Carlisle, S., Reichmuth, M., & McNeill. B. (2016). Long-term monitoring of coho salmon and steelhead trout during freshwater life stages in coastal Marin County: 2014 annual report. Natural Resource Report. NPS/SFAN/NRR—2016/1142. Fort Collins, Colorado: National Park Service. Available from https://irma.nps.gov/DataStore/DownloadFile/546839.
Carlisle, S., & Reichmuth. M. (2015). Long-term monitoring of coho salmon and steelhead trout during freshwater life stages in coastal Marin County: 2013 annual report. Natural Resource Report. NPS/SFAN/NRR—2015/956. Fort Collins, Colorado: National Park Service. Available from: https://irma.nps.gov/DataStore/DownloadFile/522417.
National Marine Fisheries Service (NMFS). (2012). Final CCC Coho Salmon ESU Recovery Plan. National Marine Fisheries Service, West Coast Region, Santa Rosa, California. Available from: http://www.westcoast.fisheries.noaa.gov/publications/recovery_planning/salmon_steelhead/domains/north_central_california_coast/central_california_coast_coho/ccc_coho_salmon_esu_recovery_plan_vol_i_sept_2012.pdf.
National Marine Fisheries Service (NMFS). (2015). Recovery Plan for North Central California Coast Recovery Domain – California Coastal Chinook Salmon, Northern California Steelhead, Central California Coast Steelhead – DRAFT. Available from http://www.nmfs.noaa.gov/pr/recovery/plans.htm.
Stillwater Sciences. (2011). Redwood Creek Watershed Assessment. Berkeley, California: Stillwater Sciences. Prepared the Golden Gate National Recreation Area. https://www.nps.gov/goga/learn/management/redwood-creek-watershed-assessment.htm.