Biological Opinions - Bureau of Reclamation

consulted on. Current monitoring data for SNS shows evidence of frequent recruitment (i.e.,
multiple size classes are present; Hewitt and Janney 2011). Therefore, it appears that droughts
and resulting low lake levels, although are likely to have adverse effects at the time they occur,
has not resulted in population-level effects that we have detected and thus, varying lake levels do
not appear to be limiting the persistence of SNS in Clear Lake.
Current data for LRS indicates that there has been little recent recruitment in Clear Lake (Hewitt
and Janney 2011), as described in the section 7, Status of the Species. The cause of this problem
is unknown. However, so called “recruitment droughts” are common among western lake
suckers (Scoppettone and Vinyard 1991); although, the causes are unknown and all western lake
suckers are affected to some degree by water management. We do not know exactly what is
limiting LRS recruitment but Project operations cannot be ruled out because there are several
potential ways that lake level management resulting in low lake levels could affect recruitment,
including drought stress and increased vulnerability to pelican predation. However, low lake
elevations below 4523 ft are likely to be uncommon events based upon the POR and therefore
not likely to be limiting the persistence of LRS in Clear Lake. Therefore, adverse effects to
rearing habitat from proposed Project operations are not likely limiting the conservation role of
critical habitat for LRS.
9.3.2.1.3 Effects to PCE 3—Food
No specific data concerning the availability of food in Clear Lake exists; however, for the
following reasons the USFWS believes this is probably not a limiting factor for the LRS and
SNS that occur there. The reservoir contains a very large amount of habitat and is productive
enough to maintain dense populations of zooplankton. Also, although juveniles weigh slightly
less at a given size in Clear Lake than do their counterparts in UKL (Burdick and Rasmussen
2012), captured individuals do not appear to be unhealthy or of low condition. Therefore, food
availability is not adversely affected by the proposed action and this PCE supports the recoverysupport
function of critical habitat for the LRS and the SNS in Clear Lake.
9.3.2.2 Effects to LRS and SNS Critical Habitat in Gerber Reservoir and Its Tributaries
9.3.2.2.1 Effects to PCE 1—Water
The proposed action does not affect PCE1 in the tributaries of Gerber Reservoir because Project
operations do not extend to the tributaries.
Water quality monitoring in Gerber Reservoir over a wide range of lake levels and years has
documented conditions that are periodically stressful, but typically adequate, for sucker survival.
Stressful water quality conditions were limited to hot weather conditions that created high water
temperatures (USBR 2001a, 2007, 2009; Piaskowski and Buettner 2003; Phillips and Ross
2012). Periodic stratification during summer and fall in the deepest portion of Gerber Reservoir
can result in DO concentrations that are stressful to suckers (Piaskowski and Buettner 2003).
However, stratification in Gerber Reservoir has been observed persisting for less than a month,
and is confined to the deepest water in a small portion of the reservoir nearest the dam
(Piaskowski and Buettner 2003). This low DO condition is likely more the result of
climatological conditions, such as high air temperatures and low wind speeds, than lake surface
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