Biological Opinions - Bureau of Reclamation

which will likely result in a relatively smaller increase in C. shasta actinospore concentrations, a
smaller reduction to habitat availability for coho salmon fry, a smaller reduction to migration rate
and survival of smolts, and a smaller reduction to water quality impairment than when the upper
Klamath Basin is experiencing relatively drier hydrologic conditions in the spring. Therefore,
flow variability under the proposed action is likely to minimize the proposed action’s adverse
effects from reductions to mainstem Klamath River flows when wet hydrological conditions
occur in the upper Klamath Basin (e.g., precipitation and snow melt).
12.4.1.2.3.5 Ramp-down Rates
Rapid ramp-down of flows can strand coho salmon fry and juveniles if mainstem flow reductions
accelerate the dewatering of lateral habitats. Stranded coho salmon fry disconnected from the
main channel are more likely to experience fitness risks, becoming more susceptible to predators
and poor water quality. Death from desiccation may also occur as a result of excessive rampdown
rates that dry up disconnected habitats. While stranding of coho salmon fry and juveniles
can occur under a natural flow regime, artificially excessive ramp-down rates exacerbate
stranding risks. Salmonid fry and juveniles are generally at the most risk from stranding than
any salmonid life stage due to their swimming limitations and their propensity to use margins of
the channel.
NMFS expects the proposed ramp-down rates when flows at IGD are greater than 3,000 cfs will
generally reflect natural flow variation since the ramp-down rates follow the rate of decline of
inflows into UKL and combine with accretions between Keno Dam and IGD. NMFS expects
any stranding that may occur at these higher flows to be consistent with rates that would be
observed under natural conditions. NMFS concluded in the 2002 and 2010 BiOps (NMFS 2002,
2010a) that the proposed ramp-down rates below 3,000 cfs adequately reduce the risk of
stranding coho salmon fry. Therefore, NMFS continues to conclude that Reclamation’s
proposed ramp-down rates are not likely to adversely affect coho salmon fry and juveniles and
thus does not analyze this part of the proposed action further in this BiOp.
12.4.1.2.4 Juvenile
Hydrologic and habitat changes can strongly affect juvenile fish survival in riverine systems
(Schlosser 1985, Nehring and Anderson 1993, Mion et al. 1998, Freeman et al. 2001, Nislow et
al. 2004). Of all the coho salmon life stages, juveniles are the most exposed to the hydrologic
effects of the proposed action. Up to 50 percent of the total parr (i.e., from mainstem redds or
tributaries) population will be affected in the mainstem Klamath River, while all smolts will use
the mainstem Klamath River to outmigrate to the ocean.
The proposed action will likely adversely affect coho salmon juveniles by decreasing water
quality (e.g., increasing water temperature, decreasing dissolved oxygen concentration),
increasing susceptibility to diseases, delaying outmigration times, and reducing habitat
availability. The amount and extent of these potential adverse effects are expected to vary
spatially and temporally, and result primarily from proposed action effects on flow. These
effects are discussed separately below for simplicity. However, note that they are interrelated
and can affect coho salmon juveniles simultaneously, sequentially, or synergistically. Also, note
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