Biological Opinions - Bureau of Reclamation

Table 8.2 UKL end-of-month elevations in ft, February through June, at the 5 to 50 percent probability levels
based on KBPM modeling of the proposed action using POR data (USBR 2012, Table 7-2).
Probability
(Percent)
February March April May June
5 4,141.2
(1,262.2 m)
10 4,141.6
(1,262.4 m)
15 4,141.7
(1,262.4 m)
20 4,142.0
(1,262.5 m)
25 4,142.0
(1,262.5 m)
30 4,142.0
(1,262.5 m)
35 4,142.1
(1,262.5 m)
40 4,142.2
(1,262.5 m)
45 4,142.3
(1,262.6 m)
50 4,142.3
(1,262.6 m)
4,142.2
(1,262.5 m)
4,142.4
(1,262.6 m)
4,142.6
(1,262.7 m)
4,142.8
(1,262.7 m)
4,142.8
(1,262.7 m)
4,142.8
(1,262.7 m)
4,142.8
(1,262.7 m)
4,142.8
(1,262.7 m)
4,142.8
(1,262.7 m)
4,142.8
(1,262.7 m)
4,142.5
(1,262.6 m)
4,142.6
(1,262.7 m)
4,142.8
(1,262.7 m)
4,143.0
(1,262.8 m)
4,143.1
(1,262.8 m)
4,143.2
(1,262.8 m)
4,143.2
(1,262.8 m)
4,143.2
(1,262.8 m)
4,143.3
(1,262.9 m)
4,143.3
(1,262.9 m)
4,142.3
(1,262.6 m)
4,142.5
(1,262.6 m)
4,142.7
(1,262.7 m)
4,142.7
(1,262.7 m)
4,142.8
(1,262.7 m)
4,142.9
(1,262.8 m)
4,142.9
(1,262.8 m)
4,142.9
(1,262.8 m)
4,143.0
(1,262.8 m)
4,143.0
(1,262.8 m)
4,141.4
(1,262.3 m)
4,141.5
(1,262.3 m)
4,141.7
(1,262.4 m)
4,141.8
(1,262.4 m)
4,141.9
(1,262.5 m)
4,142.0
(1,262.5 m)
4,142.0
(1,262.5 m)
4,142.1
(1,262.5 m)
4,142.1
(1,262.5 m)
4,142.1
(1,262.5 m)
Based on the modeled proposed action, there is a 5 percent probability that the end of March
elevation will be at or below 4,142.2 ft (1,262.5 m). Because this is 1 ft (0.3 m) higher than lake
levels were during the 2010 spawning season, it is likely there would not be adverse effects to
spawning, or if there are effects they would likely be small, because at this elevation
approximately 74 percent of composite shoreline spawning habitat is inundated at the springs to
at least 1 ft (0.3 m; Table 8.2).
Data on the effects of UKL elevations to sucker spawning behavior at shoreline springs are very
limited. However, in 2010, when the surface elevation in UKL was lower than 4,141.0 ft
(1,262.2 m) throughout much of the spawning season, roughly 15 percent fewer adult LRS were
detected at the shoreline spawning areas, and individuals spent less time at the shoreline
spawning areas than in previous years when the lake was higher (S. Burdick, USGS, pers. comm.
2012). This was especially true for females, which spent on average half as much time at the
spawning grounds compared to wetter years when lake elevations were higher. These data
support a conclusion that a UKL elevation of 4,141.0 ft (1,262.2 m) or less by the end of March
will likely adversely impact LRS spawning at the springs in UKL. Although we have data on the
percent of spawning habitat available at various UKL elevations, other than the 2010 study there
is no additional information regarding how lake levels affect sucker spawning behavior.
However, it is important to note that lower UKL elevations caused by Project operations in the
past have still supported the annual production of millions of LRS and SNS eggs and larvae at
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