Biological Opinions - Bureau of Reclamation

Stratum
Independent Extinction
Population Viability Metric
Populations
Risk
(Williams et al. 2008)
Bear River
High
Mattole River
High
Population below depensation threshold 1
Interior Eel Mainstem Eel River High
Middle Mainstem Eel
Population likely below depensation threshold 1
High
River
Upper Mainstem Eel
River
High
Population below depensation threshold 1
Middle Fork Eel River High
South Fork Eel River Moderate Population likely above depensation threshold 1
1 Based on average spawner abundance over the past three years or best professional judgment of NMFS staff.
Based on the above discussion of the population viability parameters, and qualitative viability
criteria presented in Williams et al. (2008), NMFS concludes that the SONCC coho salmon ESU
is currently not viable and is at a high risk of extinction.
The precipitous decline in abundance from historical levels and the poor status of population
viability metrics in general are the main factors behind the extinction risk faced by SONCC coho
salmon. NMFS believes the main cause of the recent decline is likely poor ocean conditions and
the widespread degradation of habitat, particularly those habitat attributes that support the
freshwater rearing life-stages of the species.
12.2.6 Factors Responsible for the Current Status of SONCC Coho Salmon ESU
When the SONCC ESU was listed, the major factors identified as responsible for the decline of
coho salmon in Oregon and California and/or degradation of their habitat included logging, road
building, grazing, mining, urbanization, stream channelization, dams, wetland loss, beaver
trapping, artificial propagation, over-fishing, water withdrawals, and unscreened diversions for
irrigation (62 FR 24588; May 6, 1997). The lack, or inadequacy, of protective measures in
existing regulatory mechanisms, including land management plans (e.g., State Forest Practice
Rules), Clean Water Act section 404 regulatory activities, urban growth management, and
harvest and hatchery management, contributed by varying degrees to the decline of coho salmon.
Below, some of these major activities are covered in more detail.
In addition to the factors responsible for the current status of the SONCC coho salmon ESU
critical habitat, ocean conditions, reduction in marine derived nutrients, artificial propagation,
commercial fisheries and small population size also affect the current status of SONCC coho
salmon ESU.
12.2.6.1 Ocean Conditions
Variability in ocean productivity has been shown to affect fisheries production both positively
and negatively (Chavez et al. 2003). Beamish and Bouillion (1993) showed a strong correlation
between North Pacific salmon production and marine environmental factors from 1925 to 1989.
Coho salmon marine survival corresponds with periods of alternating cold and warm ocean
conditions. Cold conditions are generally good for coho salmon, while warm conditions are not
(Peterson et al. 2010). Unusually warm ocean surface temperatures and associated changes in
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