EPA's Vessel General Permit and Small Vessel General

presently or historically accessible to Snake River fall-run Chinook salmon. Limiting factors
identified for Snake River fall-run Chinook salmon include: mainstem lower Snake and
Columbia hydrosystem mortality, degraded water quality, reduced spawning and rearing habitat
due to mainstem lower Snake River hydropower system, harvest impacts, impaired stream flows,
barriers to fish passage in tributaries, excessive sediment, and altered floodplain and channel
morphology (NMFS 2005b).
Snake River Spring/Summer-Run Chinook Salmon
Distribution and Description of the Listed Species
The Snake River spring/summer-run Chinook salmon ESU includes all naturally spawned
populations of spring/summer-run Chinook salmon in the mainstem Snake River and the
Tucannon River, Grande Ronde River, Imnaha River and Salmon River subbasins. Fifteen
artificial propagation programs are part of the ESU. The Interior Columbia Basin Technical
Recovery Team has identified 32 populations in five major population groups (Upper Salmon
River, South Fork Salmon River, Middle Fork Salmon River, Grande Ronde/Imnaha, Lower
Snake Mainstem Tributaries) for this species. Historic populations above Hells Canyon Dam are
considered extinct (ICBTRT 2003).
Snake River spring/summer-run Chinook salmon have a stream-type life history. Spawning
occurs in late summer and early fall and eggs incubate over the following winter and hatch in
late winter and early spring of the following year. Juveniles mature in the river for one year
before migrating to the ocean in the spring of their second year. Larger outmigrants have a
higher survival rate during outmigration (Zabel and Williams 2002, Zabel and Achord 2004).
Depending on tributary and the specific habitat conditions, juveniles may migrate widely from
natal reaches into alternative summer-rearing or overwintering areas. Spawners return to spawn
primarily as 4- and 5-year-olds after 2 to 3 years in the ocean.
Status and Trends
NMFS originally listed Snake River spring/summer-run Chinook salmon as threatened on April
22, 1992 (57 FR 14653), and reaffirmed their status as threatened on June 28, 2005 (70 FR
37160). Although direct estimates of historical annual Snake River spring/summer Chinook
salmon returns are not available, returns may have declined by as much as 97% between the late
1800s and 2000. According to Matthews and Waples (1991), total annual Snake River
spring/summer Chinook salmon production may have exceeded 1.5 million adult fish in the late
1800s. Total (natural plus hatchery origin) returns fell to roughly 100,000 spawners by the late
1960s (Fulton 1968). The 1997 to 2001 geometric mean total return for the summer run
component at Lower Granite Dam was slightly more than 6,000 fish, compared to the geometric
mean of 3,076 fish for the years 1987 to 1996 (Good et al. 2005). Good et al., (2005) reported
that risks to individual populations within the ESU may be greater than the extinction risk for the
entire ESU due to low levels of annual abundance and the extensive production areas within the
Snake River basin. Although the average abundance in the most recent decade is more abundant
than the previous decade, there is no obvious long-term trend.
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