Historic and recent occurrence of Coho Salmon (Oncorhynchus kisutch) in California streams within the Southern Oregon/ Northern California Evolutionary Significant Unit

SONCC ESU Coho Salmon Status and Viability Assessment
California represents the southern extent of coho salmon (Oncorhynchus kisutch) distribution in North America. Two coho salmon Evolutionarily Significant Units (ESU’s) defined by the National Oceanic and Atmospheric Administration (NOAA) occur in the northwest portion of California. Coho salmon populations occurring within The Southern Oregon/ Northern California Coastal (SONCC) ESU (Figure 1) have declined substantially leading to protections under the federal (ESA) and California (CESA) Endangered Species Acts (Federal Register 1997, CDFG 2002). Both listings have initiated the development of recovery plans defining delisting goals (CDFG 2004, NOAA in progress), determination of the population structure within the ESU (Williams et al. 2006), and defining a population monitoring framework to measure population trends and recovery progress (Williams et al. 2008, Adams et al. 2011). 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 is the tool used to minimize uncertainties around extinction risk and recovery status of the SONCC ESU as a whole. Two additional spatially explicit criteria needed to assess ESU viability include: 1) population representation, and 2) redundancy and connectivity of populations (Williams et al. 2008). These criteria help define the spatial arrangement and total number of populations needed for ESU‐level monitoring. Therefore, to determine recovery for the
SONCC ESU, numerous long‐term population monitoring programs addressing coho salmon productivity and life history attributes need to be established across the ESU.