Biological Opinions - Bureau of Reclamation

Although entrainment of LRS and SNS is likely to occur at other Project diversions under the
proposed action, the only facility where entrainment has been measured is at Gerber Dam, where
Reclamation estimates that 250 juvenile SNS could be entrained annually (USBR 2012).
Although no entrainment estimates are available for Clear Lake Dam, we assume entrainment of
larval suckers is occurring there because the dam is downstream of the Willow Creek mouth
where larval suckers enter the lake. However, suckers larger than approximately 35 mm total
length are not likely entrained because of the small size of the openings in the fish screen.
Entrainment rates at these facilities are likely much lower than at the Link River Dam because
there are fewer reproducing adults present in these areas when compared to UKL. Therefore at
these other facilities, we assumed that entrainment take would be 10 percent of that which is
estimated to be occurring at the Link River Dam where entrainment was measured. The basis for
that assumption is the following: (1) the combined total adult sucker populations in Clear Lake,
Gerber Reservoir, Tule Lake, Keno Reservoir, and Lost River is approximately half of those in
UKL; (2) larvae would be present earlier in the season and for a shorter period in Gerber
Reservoir and Clear Lake in comparison to UKL because of the earlier run-off of snow-melt in
the Lost River sub-basin; (3) flows from Clear Lake and Gerber Reservoir Dams are much less
than at the Link River Dam when larvae are present because of the small demand for irrigation
on the east side of the Project at that time; (4) flows at the Link River Dam in the spring are high
due to the downstream needs of coho salmon; and (5) water quality is better in Clear Lake and
Gerber Reservoir in comparison to UKL, so there would be less of an effect of water quality on
entrainment rates at Clear Lake and Gerber Reservoir, as explained in the Effects of the Action
(section 8).
Based on this, we estimate that total annual entrainment take as harm as a result of the
implementation of the proposed action by all Project water-management facilities other than at
the A Canal and Link River Dam equals up to 2,700 larvae, 60 juveniles, and 10 adults. The
numbers of LRS and SNS annually harassed by these facilities is estimated to be up to 134,000
larvae, 3,000 juveniles, and 10 adults (Table 13.2). Note that we estimated that the numbers of
adults harassed and harmed per year would be up to 10, which is the smallest number that likely
could be detected.
13.2.1.5 Entrainment Estimates for the Entire Project
Based on the analysis presented above, we estimate that the total annual entrainment take of LRS
and SNS at all Project diversions, as a result of implementing the proposed action, could be up to
350,672 harmed and 1.88 million harassed; most of these will be larvae (Table 13.2).
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