Coho and steelhead populations in the Lagunitas Creek watershed are threatened by low returns in certain years. Stillwater Sciences examined potential limiting factors and restoration actions using a combination of existing data synthesis and focused field research. We hypothesized that sediment infiltration into redds may be causing this, and implemented a pilot study to assess possible mechanisms. Stillwater Sciences has been conducting investigations on behalf of several agencies and stakeholders in the Lagunitas Creek watershed since 2004.
A conceptual model was first developed for each salmonid species using existing information, tailored fish population modeling, and input from local experts and technical advisors. An iterative approach of hypothesis generation and testing using this available information was then used to identify data gaps for further study. To test whether redd scour and/or redd entombment was responsible for low juvenile estimates in some years, we deployed and monitored coho redds throughout the fall breeding season, assessed over-wintering habitat, and trapped smolts in the spring. Because there is a high level of public support and interest within the watershed, Stillwater Sciences trained and helped organize various stakeholder and volunteer organizations to help with daily trap monitoring. While results were not definitive, the habitat assessments did provide an understanding of in-channel physical attributes and processes on endangered salmonid populations, with direct implications for watershed-wide fisheries management and restoration priorities.
We are currently quantifying sediment production from hillslope and channel sediment sources to the mainstem channel and constructing an average-annual sediment budget for the Lagunitas Creek watershed for the recent past (25 years). Results from this study will provide the data necessary to develop recommendations to reduce sediment inputs and will ultimately help in the formulation of a watershed-wide TMDL aimed, in part, at addressing fine sediment-related factors limiting the abundance of coho salmon and steelhead within the Lagunitas Creek watershed. For more information, download the full Sediment Delivery Assessment.
Lagunitas Creek, Marin County, California
Marin County Resource Conservation District
San Francisco Regional Water Quality Control Board
Marin Municipal Water District
Marin County Department of Public Works
Association of Bay Area Governments
Lagunitas Creek, a small watershed in Marin County, CA supports one of the largest and most stable coho salmon populations south of the Noyo River within the Central California Coast ESU.View the gallery