Biological Opinions - Bureau of Reclamation

in fewer larvae and juveniles, and therefore entrainment should be much less now than it was in
the late 1990s when it was measured.
13.2.1.3 Link River Dam Entrainment Estimates
At the Link River Dam, up to 1.34 million larvae could be entrained into the spillway gates every
year, based on an analysis we developed for the 2008 BiOp (USFWS 2008), and assuming
entrainment had likely decreased by 80 percent because of declines in adult populations in UKL,
as described above. When PacifiCorp’s Habitat Conservation Plan (HCP) is finalized later in
2013, nearly all of the Link River flow will pass through the spillway gates of the dam, and
consequently we assumed all of the take occurring there will be attributable to the Project.
Because we do not know exactly when the HCP will be in effect, for purposes of estimating take
we assume all of the take at Link River Dam over the term of the BiOp is attributable to
Reclamations actions. We further assumed that 2 percent of the larvae (26,800) passing through
the spillway of the Link River Dam will be harmed (USFWS 2007). This estimate is based on a
review of the literature on the effects of dams on fish that have documented injuries resulting
from physical strikes with objects and pressure changes associated with passing through
spillways (USFWS 2007). Additionally, some mortality could occur as a result of predators
attacking disoriented suckers following spillway passage, and infections resulting from nonlethal
wounds incurred during spillway passage. Based on this analysis, we estimate that up to 26,800
sucker larvae could be harmed every year at the Link River Dam as a result of the proposed
action.
Additionally, we estimate that up to 30,000 age-0 juveniles could be entrained at the dam every
year. Of these we assume 98 percent (29, 400) are harassed and 2 percent (600) of these are
likely harmed by passing through the spillway gates. In most years, the number of entrained
suckers will likely be much lower because high production years are infrequent, as mentioned
above.
Annual entrainment of adult suckers at the Link River Dam, once PacifiCorp’s HCP is in place,
is estimated to be approximately 40. Assuming that 2 percent of these are injured as a result of
physical strikes with objects and pressure changes associated with passing through the spill
gates, the number of adults taken by harm would be 1.
We assume all suckers passing through the Link River Dam spillway gates will be harassed
because entrainment is likely to disrupt normal behaviors such as feeding and predator
avoidance. Thus, we estimate up to 1.34 million larvae, 29,400 juveniles, and 40 adult suckers
could be harassed annually as a result of entrainment. Maximum annual lethal take at the Link
River Dam is estimated to be up to 26,800 larvae, 600 juveniles, and 1 adult, as a result of
entrainment.
13.2.1.4 Entrainment at Other Project Facilities
Entrainment is also likely occurring at other Project facilities, such as at Clear Lake and Gerber
Dams, Lost River Diversion Channel, and other diversions, as discussed in the Effects of the
Action (section 8), but we lack the data to estimate take at these facilities.
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