Our new Biological Assessment is out - Klamath Basin Crisis

Klamath Project Operations Biological Assessment
Coho Salmon: Coho Salmon Life History, Abundance, and Trends
In 1997, USFWS concluded that juvenile coho salmon likely rear throughout the
year in the main stem Klamath River between IGD and Seiad Creek. Consistent
with the findings of USFWS are the results of CDFG’s 2001 study that indicates
the majority of juvenile coho salmon emigrated from the Scott and Shasta Rivers
during the period of April 23 through June 24, 2001 (p. 20 NMFS 2002 BO).
Both USFWS (1997) and CDFG (1994) indicated that coho salmon fry emigrated
from some tributaries to the main stem Klamath River soon after emergence.
Further evidence of coho salmon fry emigrating from tributaries to the main stem
Klamath River has been observed by the Yurok Tribe (NMFS 2002).
In much of the main stem Klamath River, juvenile coho salmon are forced to seek
thermal refugia throughout most of the river during the hottest part of summer
(Belchik 2003; Sutton et al. 2007). Summer water temperatures in the Klamath
River below Seiad Creek far exceed the preferred range for coho salmon. Thus,
rearing capacity in much of the main stem is determined by the availability of
thermal refugia, as well as the number of juvenile coho salmon each of these
refugia can support. However, summer rearing in non-natal tributaries has the
potential to increase the summer carrying capacity of the Klamath River system
and the high food abundance in the Klamath River main stem increases the
energetic scope of activity of coho salmon that use the main stem on a seasonal
basis.
Adult and Juvenile Observation Summary
In summary, adult observations within the Klamath River Basin 10 show
considerable year-to-year variation. However, these observations indicate an
increasing trend in abundance in recent years for Trinity River populations, while
the non Trinity River Klamath River populations appear to be more stable or
slightly decreasing; although the correlations are not significant (p > 0.05). In
regards to juvenile observations, the traps have had inconsistent periods of
operation (days trapped); however the data collected do indicate a possible
increasing trend in relative abundance, at least for the Scott River.
Coho Salmon Run Size Estimates and Trends
NMFS, in its administration of the ESA, defines anadromous species by
Evolutionarily Significant Units (ESUs). An ESU is a population or group of
populations of salmon that are substantially reproductively isolated from other
populations and contribute substantially to the evolutionary legacy of the
biological species. The Southern Oregon/Northern California Coast (SONCC)
10 This is true particularly for the young of the year information at the Willow Creek and Big
Bar rotary screw traps.
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