Biological Opinions - Bureau of Reclamation

in UKL in late August and early September and in 1997 over 2,000 adult suckers were found
dead from late July to late September (Perkins et al. 2000b). In both years, ammonia levels were
high and DO levels low for several weeks prior to the die-offs. For short periods, usually less
than 1 day, DO concentrations ranged from 0 to 2.2 mg/L, which is within the lethal range for
suckers (Perkins et al. 2000b). Additionally, at the lowest lake levels during late summer months
there is an increased risk of concentrating suckers in limited areas of deeper water where disease
could be more readily spread among individuals. Given that the new bathymetric data has not
undergone, QA/QC review, and given the status of adult suckers, it is prudent to assume that
depths at the entrance to Pelican Bay could be shallower than indicated by the new data. At the
minimum proposed elevation of 4,137.7 ft (1,261.2 m), depths are likely under 4 ft (1.1 m) and
pose a rare, but potentially high, risk to adult suckers. Furthermore, these low water levels make
it more likely that the lake would not provide adequate spawning and rearing habitat the next
spring if inflows were inadequate.
Under the proposed action, a surface elevation of 4,138.5 ft (1,261.4 m) provides approximately
13,000 ac (5,260 ha; about 46 percent) of available habitat in the portion of UKL north of Bare
Island (USBR 2012, Tables 7-7 and 7-8) at depths of 6.5 ft (1.9 m) or greater without the
inclusion of the reconnected Williamson River Delta. Assuming that conditions similar to those
at the 5 percent probability level are experienced, such as during 1992 and 1994, it is anticipated
the proposed action will result in lake elevations below 4,138.2 ft (1,261.3 m) that could provide
only about 20 percent of available habitat in the northern end of UKL at depths between 6 and 9
ft (2 and 3 m) through the end of September (USBR 2012, Tables 7-6 and 7-8). Elevations
below 4,138.2 ft (1,261.3 m) occurred three out of 31 years in the modeled POR.
Under proposed Project operations, there appear to be thousands of acres of potential habitat
during the late summer for adult suckers, even at the lowest lake levels. However, this considers
only one variable, depth, whereas radio-tracking shows that adult suckers occur seasonally in
limited areas of the lake and those areas are sometimes species-specific. Areas of high seasonal
use by adult suckers include Ball Bay, and the areas north of Ball Point, between Ball Bay and
Fish Banks, and between Eagle Ridge and Bare Island (Reiser et al. 2001, Banish et al. 2009).
SNSs, especially, show a preference for Ball Bay, whereas LRSs were frequently located off of
Ball Point (Banish et al. 2009, Figure 2). Additionally, both species used the area of the lake
north of Ball Bay to the mouth of Pelican Bay (Banish et al. 2009). We presume this distribution
is due to selection of habitats beneficial to the LRS and the SNS for some reason(s), such as
abundant food, fewer predators, and/or better water quality, in addition to adequate depth.
It is unclear how seasonal changes in lake levels affect the distribution of adult suckers, but low
lake levels in very dry years could reduce use of shallow areas such as in Ball Bay. Thus, low
lake levels (i.e., those below 4,138.2 ft [1,261.3 m]) in September potentially could adversely
affect adult suckers by limiting their access to some preferred habitats. Recent information
shows that older juvenile suckers use nearshore shallow habitats with some frequency along the
western lake shore and near the Williamson River Delta (Burdick and VanderKooi 2010;
Burdick 2012a, b). This suggests that low lake levels could also affect older juvenile sucker
distribution if they show habitat preferences.
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