Biological Opinions - Bureau of Reclamation

the amount of genetic and phenotypic diversity of a species by homogenizing once disparate
traits of hatchery and natural fish. The result can be progeny with lower survival (McGinnity et
al. 2003, Kostow 2004) and ultimately, a reduction in the reproductive success of the natural
stock (Reisenbichler and McIntyre 1977, Chilcote 2003, Araki et al. 2007, Chilcote et al. 2011),
potentially compromising the viability of natural stocks via out breeding depression
(Reisenbichler and Rubin 1999, HSRG 2004). Williams et al. (2008) considers a population to
be at least at moderate risk of extinction if the proportion of naturally spawning fish that are of
hatchery origin exceeds 5 percent.
Flagg et al. (2000) found that, depending on the carrying capacity of the system, increasing
release numbers of hatchery fish often negatively impacts naturally-produced fish because these
fish can get displaced from portions of their habitat. Competition between hatchery and
naturally-produced salmonids can also lead to reduced growth of naturally produced fish
(McMichael et al. 1997). Kostow et al. (2003) and Kostow and Zhou (2006) found that over the
duration of the steelhead hatchery program on the Clackamas River, Oregon, the number of
hatchery steelhead in the upper basin regularly caused the total number of steelhead to exceed
carrying capacity, triggering density-dependent mechanisms that impacted the natural
population. Competition between hatchery and natural salmonids in the ocean can also lead to
density-dependent mechanisms that affect natural salmonid populations, especially during
periods of poor ocean conditions (Beamish et al. 1997, Levin et al. 2001, Sweeting et al. 2003).
12.2.6.4 Commercial and Recreational Fisheries
12.2.6.4.1 Tribal Fishery
Tribal harvest was not considered to be a major threat to the SONCC coho salmon ESU when the
ESU was listed under the ESA (60 FR 38011; July 25, 1995). Klamath basin tribes (Yurok,
Hoopa, and Karuk) harvest a relatively small number of coho salmon for subsistence and
ceremonial purposes (CDFG 2002b). Coho salmon harvested by Native American tribes is
primarily incidental to larger Chinook salmon subsistence fisheries in the Klamath and Trinity
rivers. Estimates of the harvest rate for the Yurok fishery are available since 1992, and averaged
4 percent between 1992 and 2005, and 5 percent between 2006 and 2009 (Williams 2010). The
average annual harvest rate by the Hoopa Tribe accounts for less than 3 percent of the total
number of adult spawners returning to the Trinity River (Naman 2012).
12.2.6.4.2 Non-tribal Commercial Fishery
Commercial fisheries have been identified as a major factor in the decline of the SONCC coho
salmon ESU (60 FR 38011; July 25, 1995 and 69 FR 33102; June 14, 2004). However, coho
salmon-directed fisheries and coho salmon retention have been prohibited off the coast of
California since 1996. Therefore, the SONCC coho salmon ESU ocean exploitation rate is low.
Incidental mortality occurs as a result of non-retention impacts in California and Oregon
Chinook-directed fisheries and in Oregon’s mark-selective coho fisheries.
The Rogue/Klamath coho salmon ocean exploitation rate forecast time series from 2000 to 2010
(Figure 12.12) is the best available measure of ocean exploitation rate for the SONCC coho
salmon ESU. This rate had been stable and averaged 6 percent over 2000 to 2007 prior to falling
to 1 percent and 3 percent in 2008 and 2009, respectively, due to closure of nearly all salmon
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