Biological Opinions - Bureau of Reclamation

the high risk depensation level, the average abundance of the past three years is slightly greater
than the high risk abundance threshold. Therefore, the Scott River Population currently has a
moderate risk of extinction.
Fish surveys of the Scott River and its tributaries have been occurring since 2001. These surveys
have documented coho salmon presence in 11 tributaries, with the six most productive of these
tributaries consistently sustaining rearing coho salmon juveniles in limited areas. The five other
tributaries do not consistently sustain juvenile coho salmon, indicating that the spatial structure
of this population is restricted by available rearing habitat. The spatial structure of this
population appears restricted. The diversity of this population has not been studied.
12.3.2.5 Salmon River
Surveys suggest that specific spawning areas are re-visited each year and that fish in certain
spawning areas may have specific life history traits, such as different run timing (Pennington
2009). Based on the low hatchery influence and small population size, the genetic structure of
this population likely retains much of its wild character, but overall the level of natural genetic
diversity has likely declined.
With limited data, Ackerman et al. (2006) estimated fewer than 50 spawners for the Salmon
River coho salmon population for 2001, 2002 and 2003. Since 2002, the Salmon River
Restoration Council along with CDFW, the Karuk Tribe, the USFS and the USFWS have
conducted spawning and juvenile surveys throughout the watershed. Annual adult coho salmon
abundance surveyed in the Salmon River has varied between 0 and 14 spawning adults since
2002 (Salmon River Restoration Council 2006, 2010). Between 2002 and 2007 only 18 adults
and 12 redds (average of 4 spawners per year) were found in the 25 km of surveyed habitat.
Without any new information to show coho salmon spawner abundance increased, NMFS
continues to estimate the total Salmon River spawner abundance as less than 50 individuals,
which is well below the depensation threshold. An adult population of 50 or less would
represent a population with limited spatial structure. Based on the estimated spawning
abundance and likely limited spatial structure, the Salmon River coho salmon population is at
high risk of extinction (Table 12.3).
12.3.3 Factors Affecting Coho Salmon in the Action Area
In addition to the habitat conditions and the factors affecting the SONCC coho salmon ESU
critical habitat in the action area that are described in the Environmental Baseline of Coho
Salmon Critical Habitat in the Action Area section, hatcheries, fish harvest, pinniped predation,
and activities that have incidental take permits or exemptions also affect the current status of
SONCC ESU coho salmon in the action area.
12.3.3.1 Hatcheries
Two fish hatcheries operate in the Klamath River basin, the Trinity River Hatchery near the town
of Lewiston and the IGH on the mainstem Klamath River near Hornbrook, California. Both
hatcheries mitigate for anadromous fish habitat lost as a result of the construction of dams on the
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