Biological Opinions - Bureau of Reclamation

A small number of coho salmon (e.g., fewer than approximately 50 each year) spawn in the
mainstem Klamath River, and thus a relatively small number of embryos and fry are expected to
be present in the mainstem each winter and spring. In addition, coho salmon fry from tributaries
emigrate into the mainstem Klamath River as a result of ecological conditions (e.g., high flow
displacement or deleterious tributary conditions [Chesney et al. 2007]) or behavioral tendencies.
However, most coho salmon fry from the tributaries (i.e., ≥ 50 percent) are assumed to rear in the
tributaries.
Juveniles likely rear in the mainstem throughout the year, and consist of parr and smolts.
Juvenile coho salmon have been observed residing within the mainstem Klamath River
downstream of Shasta River throughout the summer and early fall in thermal refugia during
periods of high water temperatures (>22 °C). Coho salmon parr may be present in the mainstem
from the time they leave the tributaries to the following winter. However, most parr from the
tributaries (i.e., ≥ 50 percent) are assumed to rear in the tributaries.
Coho salmon smolts are expected to migrate to the mainstem Klamath River beginning in late
February, with most natural origin smolts outmigrate to the mainstem during March, April and
May (Wallace 2004). Courter et al. (2008), using USFWS and CDFW migrant trapping data
from 1997 to 2006 in tributaries upstream of and including Seiad Creek (e.g., Horse Creek,
Shasta River, and Scott River), reported that 56 percent of coho smolts were trapped from April
1 through the end of June.
Once in the mainstem, smolts move downstream fairly quickly, with estimated median migration
rates of 13.5 miles/day (range -0.09 to 114 miles/day) for wild coho salmon and 14.6 miles/day
(range -2.3 to 27.8 miles/day) for hatchery coho salmon (Stutzer et al. 2006). Beeman et al.
(2012) found that wild coho salmon smolts released near IGD had a median travel time of 10.4
and 28.7 days in 2006 and 2009, respectively, to the estuary. The maximum recorded time of
wild coho salmon smolts traveling on the mainstem from IGD to the estuary was 63.8 days
(Beeman et al. 2012).
Table 12.5. A summary of the coho salmon life stage exposure period to project-related flow effects.
Life Stage Coho Salmon Population(s) General Period of exposure when
individuals are in the mainstem
Adults
Upper Klamath River
September to mid-January
Embryos to preemergent
fry
Fry
Juvenile (parr)
Juvenile
(smolts)
Upper Klamath River
Upper Klamath, Shasta River,
Scott, and Middle Klamath
rivers
Upper Klamath, Shasta River,
Scott, and Middle Klamath
rivers
November to mid-March
March to mid-June
May to February
March to June
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