Coho Salmon Crisis in the Central California Coast ESU

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A watershed-related issue examined by the ENVS 560/L Watershed Systems class at CSUMB.


Current Issue

Marin County's Lagunitas Creek Watershed, once held out as a statewide model for fisheries restoration, is now hanging in the balance with an unprecedented 90% decline in coho salmon returning to spawn so far this year[1]. The primary reason for the decline of coho salmon in Lagunitas Creek appears to be due to the construction of the Kent and Nicasio Reservoirs, which restricted the fish to the lowermost portion of the creek. Construction of the reservoirs has prevented recruitment of new gravel into most of the system resulting in a streambed dominated by relatively large and angular particles. Most spawning now takes place in San Geronimo Creek, an unregulated tributary, and the region immediately downstream of its confluence with Lagunitas Creek.[2] In addition, fisheries and watershed biologists say that several years of exceptionally reduced winter rainfall have contributed to the worst coho salmon return in recorded history. The decreased rainfall translates as reduced creek flow which prevents salmon from effectively swimming upstream and being more vulnerable to predation in the open ocean.


Lagunitas Creek Watershed offers unique spawning grounds in that it is in the midst of a developed area. While historic Coho salmon runs numbered in the thousands a hundred years ago, subsequent redwood logging operations followed by road and housing construction reduced the original salmon habitat to 40% of its original size. The seven dams spread throughout the area also significantly blocked off historic salmon habitat while also reducing gravel needed for spawning while also increasing creek sediment. In the early 1980s, restoration efforts started with the lobbying of a Trout Unlimited to the county make efforts to halt the salmon fishery decline.


This unprecedented decline is particularly troublesome because the Lagunitas Creek Watershed is considered one of California's most critical ecosystems for endangered coho salmon[4]. Historically the Lagunitas Creek Watershed has supported California's largest wild salmon run, regularly supporting 10% of the state's Coho Salmon population[5]. The Lagunitas Creek watershed salmon population is also considered considered critical for the coho salmon population of the entire central California coast [3]. Salmon have been regularly taken from this watershed to supplement populations in regional watersheds There are now probably less than 5,000 native coho salmon (with no known hatchery ancestry) spawning in California each year, many of them in populations of less than 100 individuals. Coho populations today are probably less than 6% of what they were in the 1940s, and there has been at least a 70% decline since the 1960s. There is every reason to believe that California coho populations, including hatchery stocks, will continue to decline. The reasons for the decline of coho salmon in California include: stream alterations brought about by poor land-use practices (especially those related to logging and urbanization) and by the effects of periodic floods and drought, the breakdown of genetic integrity of native stocks, introduced diseases, over harvest, and climatic change. This local scale salmon decline is consistent with the recent plummeting of statewide salmon populations that prompted the chinook salmon fishery collapse and subsequent closure along the west coast.


Lagunitas Creek Watershed winds through San Geronimo Valley on the northwest side of Mount Tamalpais in Marin County, California[6]. The Lagunitas Creek Watershed coho salmon are part of the Central California Coast Evolutionarily Significant Unit (ESU) that extends from Punta Gorda in northern California south to and including the San Lorenzo River in central California[7]. This ESU status was designated 1999[4].

Resource/s at stake

Fishery biologists fear that the severe decline in returning Coho Salmon may result in a spawning failure and possible extinction for the year. Biologically speaking, diminished population size can negatively effect the genetic diversity of the population and reduce fitness or viability for the future. Genetic diversity is a significant concern with with most native spawning coho salmon populations consisting of less than 100 individuals[1]. Economically, reduced salmon numbers can negatively impact human communities that have relied on salmon fishing for income and tourism.


  • SPAWN (Salmon Protection and Watershed Network)
    • Created in 1996, SPAWN sponsors salmon-watching creek walks during spawning season and has saved more than 15,000 salmonids from diminishing summer pools.
  • Trout Unlimited
    • Trout Unlimited- lobbyists
  • The Marin Municipal Water District
    • Required by the state to help coho salmon to mitigate any negative impacts of Peter's Dam, started counting coho redds (salmon spawning 'nests')in the early 1990s and now works with SPAWN to monitor releases from the dam, install woody debris in the creeks and replant vegetation.
  • National Marine Fisheries biologists
    • Are interested in monitoring and studying salmon populations.
  • National Oceanic and Atmospheric Administration (NOAA)
    • Study and monitor endangered species.
  • Area Residents
    • Community members and schools organize programs to inform students and other community members about the historic coho migration.
  • Regional Fishers & Fish-related industry
    • Many communities rely on the fish as a source of income.

Laws, policies, & regulations

  • In 2005 coho salmon were listed as endangered under the United States Federal Endangered Species Act[8]


  • Climate change may be contributing to warmer and drier winters with less rainfall. The resulting creek flow limits salmon ability to navigate to the spawning grounds.
  • The salmon form part of the food web that with their disappearance may become deranged
  • The Coho salmon habitat and watershed integrity were negatively impacted by logging and development which reduced available habitat, stream connectivity and flow[3]. The resulting decreased creek gravel and increased sediment contribute to reducing critical spawning habitat [2].

Scientific questions

  • Examining whether restoration efforts actually improved the watershed conditions?
  • Examining whether reduced creek water flow is more due to changes in weather patterns alone or a combination of weather patterns in conjunction with development in the watershed reducing its capacity or decreasing flow.

Relevant scientific tools

  • Fish could be tagged and tracked, but that might be difficult considering life span and size.
  • Fish that are assisted out of drying ponds could be monitored for survival rate with GPS tracking information.
  • Weather models could be implemented to predict required rainfall patterns.
  • Genetic tools to investigate genetic diversity of coho salmon population and what percentage is "pure wild type" versus those with stock ancestry.

Future research

  • Given unlimited money the remaining population's genotype could be assessed to deem if there is sufficient diversity remaining for re-population. If so, a breeding program that tracks and pairs individuals could be started to increase genetic diversity. Especially important if this population was used to restock other locations. Also genetic analyses could be done to test whether distinct morphotypes reflect genotype diversity.

Notes and References

  1. 1.0 1.1 Fimrite, P. 2009. Crisis Situation for Marin's coho salmon. San Francisco Chronicle. 01092009 Section B1
  2. 2.0 2.1 Brown, L.R., Moyle, P.B. 1991. Historical Decline and Current Status of Coho Salmon in California. North American Journal of Fisheries Management
  3. 3.0 3.1 3.2 Brown, L.R., Moyle, P.B. & Yoshiyama, R.M. 1994. Historical Decline and Current Status of Coho Salmon in California. North American Journal of Fisheries Management 14.2:237–261
  4. 4.0 4.1 NOAA Fisheries Office of Protected Resources



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