EPA's Vessel General Permit and Small Vessel General

other specified estuarine waters. These areas are important for the species’ overall conservation
by protecting quality growth, reproduction, and feeding. Factors contributing to the downward
trends in this ESU include reduced access to spawning/rearing habitat, possible loss of genetic
integrity through population bottlenecks, inadequately screened diversions, predation at artificial
structures and by nonnative species, pollution from Iron Mountain Mine and other sources,
adverse flow conditions, high summer water temperatures, unsustainable harvest rates, passage
problems at various structures, and vulnerability to drought (Good et al. 2005).
Final Protective Regulations
On June 28, 2005, as part of the final listing determinations for 16 ESUs of West Coast salmon,
NMFS amended and streamlined the 4(d) protective regulations for threatened salmon and
steelhead (70 FR 37160) as described in the Protective Regulations for Threatened Salmonid
Species section of this document. Under this change, the section 4(d) protections apply to
natural and hatchery fish with an intact adipose fin, but not to listed hatchery fish that have had
their adipose fin removed prior to release into the wild. The amended June 2005 4(d) rule
applies to the Snake River fall-run Chinook salmon ESU.
Snake River Fall-Run Chinook Salmon
Distribution and Description of the Listed Species
The Snake River fall-run Chinook salmon ESU includes all naturally spawned populations of
fall-run Chinook salmon in the mainstem Snake River below Hells Canyon Dam, and in the
Tucannon River, Grande Ronde River, Imnaha River, Salmon River and Clearwater River
subbasins. Four artificial propagation programs are part of this ESU.
Historically, the primary fall-run Chinook salmon spawning areas occurred on the upper
mainstem Snake River (Connor et al. 2005). A series of Snake River dams blocked access to the
upper reaches, which significantly reduced spawning and rearing habitat. Consequently, salmon
now reside in waters that are generally cooler than pre-dam habitats. Currently, natural
spawning occurs at the upper end of Lower Granite Reservoir to Hells Canyon Dam, the lower
reaches of the Imnaha, Grande Ronde, Clearwater and Tucannon rivers and small mainstem
sections in the tailraces of the lower Snake River hydroelectric dams.
Adult Snake River fall-run Chinook salmon enter the Columbia River in July and August, and
spawning occurs from October through November. Juveniles emerge from the gravels in March
and April of the following year, moving downstream from natal spawning and early rearing areas
from June through early autumn. Prior to dam construction, fall Chinook salmon were primarily
ocean-type (migrated downstream and reared in the mainstem Snake River during their first
year). However, today both an ocean-type and reservoir-type occur (Connor et al. 2005). The
reservoir-type juveniles overwinter in pools created by dams before migrating to sea; this
response is likely due to early development in cooler temperatures which prevents rapid growth.
Phenotypic characteristics have shifted in apparent response to environmental changes from
hydroelectric dams (Connor et al. 2005). Migration downstream appears to be influenced by
flow velocity within both river and reservoir systems (Tiffan et al. 2009).
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