Coho Distribution

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This report summarizes five years of data collection on salmonid populations in the Smith River basin based on the California Coastal Monitoring Program (CMP). We conducted this effort for five years from 2011-2016 based on funding through the Fisheries Restoration Grant Program.

We continually investigated two population viability metrics of salmonids in the Smith River basin (California and Oregon), with ESA listed coho salmon (Oncorhynchus kisutch) as the focal species. First, we monitored we monitored adult salmonid escapement and distribution from 2011 to 2016 using live fish, carcass, and redd counts as defined in California’s Coastal Salmonid Monitoring Plan. The spawner survey sample frame includes 161.8 kilometers of potential spawning habitat divided into 68 reaches and 30 sub-reaches. Over the five years we completed 1896 spawning ground surveys across 87 survey reaches. During this time we made 1380 observations of live adult coho salmon ranging from 125 in 2015-2016 to 494 in 2013-2014, and recovered 196 coho salmon carcasses ranging from 15 in 2014-2015 to 82 in 2011-2012. Across all five years most coho salmon observations and carcass recoveries occurred in Mill Creek, the exceptions were eight live individuals and 4 carcasses in Rowdy Creek, one carcass in Morrison Creek, and one live individual in Hurdygurdy Creek. Last, we were able to verify 293 individual coho salmon redds throughout the five years of sampling.

Second, we estimated the summer spatial structure of juvenile salmonids and adult coastal cutthroat trout annually from 2012 to 2016 using multiple-pass snorkel surveys in an occupancy modeling framework. The spatial structure sample frame includes 167 reaches totaling 298.1 kilometers of summer rearing habitat in the Smith River basin. Over the five years we completed surveys of 323 reaches totaling 608 cumulative stream kilometers and a total of 7254 pools. We documented coho salmon occupying 64 of the 157 reaches individually surveyed at least once over the five years. Coho salmon maintained patchy distributions relative to the sampling frame over the five years. Based on the summer distribution data collected throughout the basin, we describe five extant juvenile coho salmon patches. Four of the five patches are maintained by independent spawning sub-populations and we consider the lower mainstem Smith River and tributaries to be the only significant non-natal coho salmon rearing patch.

More Information

The Smith River Alliance and the California Department of Fish and Wildlife launched a partnership in 2011 to assess and monitor coho salmon in the Smith River basin. Under a grant from the Fisheries Restoration Grant Program, SRA assembled a crew of experienced fish biologists to implement the survey plan designed by Justin Garwood, CDFW.

Over five years we implemented a project designed to further develop and implement a strategic, long-term population assessment and monitoring program for coho salmon using standardized methods defined in the Coastal Salmonid Monitoring plan (CMP), (Adams et al. 2011).

The primary objectives were: (1) to monitor the annual abundance of adult Coho Salmon in the Smith River population unit using spawning ground surveys; (2) to monitor the occupancy and spatial distribution of juvenile coho salmon via snorkel surveys in the Smith River population unit; and (3) to incorporate spawning ground surveys occurring in Mill Creek into meeting the goals of a Life Cycle Monitoring Station (LCS).

Project Background

Marked population declines of coho salmon populations in all freshwater habitats in California have led to both federal and state listings under the federal (ESA) and California (CESA) Endangered Species Acts (Federal Register 1997, CDFG 2002). Both listings have initiated the development of recovery plans which include delisting goals (CDFG 2004, NOAA (SONCC recovery document in review) for the Southern Oregon Northern California Coho (SONCC) ESU. This unit has been defined as the scale used to assess population viability (Williams et al. 2006).

NOAA established four viable salmon population (VSP) parameters to determine a population’s risk of extinction. These parameters include: abundance, productivity (population growth rate), spatial structure, and diversity in life history (McElhany et al. 2000). Trend monitoring for these VSP parameters within specific functionally independent populations is the tool used to minimize uncertainties around extinction risk and recovery status of the SONCC ESU as a whole. For a coho salmon population to meet or exceed a viable threshold, it must show a low risk of extinction over 100 years (McElhany et al. 2000). Therefore, to determine recovery for the SONCC ESU, numerous long-term population monitoring programs need to be established across the ESU. The Smith River basin has been identified as a functionally independent coho salmon population in the central diversity strata for the SONCC ESU by NOAA (McElhany et al. 2000, Williams et al. 2006, Williams et al. 2008) and is proposed to represent a “Core population” (NOAA SONCC recovery document in review).

Furthermore, the Smith River basin is recognized as a recovery unit by CDFG (CDFG 2004) in the SONCC ESU. With the exception of one long-term monitoring program in Mill Creek (McLeod and Howard 2010), sparse information exists regarding the distribution and abundance of coho salmon in the Smith River. All previous studies appear to be juvenile focused; with repeated adult counts having occurred only in index sections of Mill Creek (McLeod and Howard 2010). A review of coho salmon distribution by Garwood (in review) identified 34 streams as having historic occurrence in the Smith River.