Biological Opinions - Bureau of Reclamation

Based on surface elevations from the POR for Gerber Reservoir, the proposed action, which
maintains the current lake management of a minimum surface elevation of 4,798.1 ft (1,462.5 m)
at the end of September, will likely maintain access to spawning habitat during spring the
following year. Therefore, the proposed action in Gerber Reservoir is likely to provide adequate
access to spawning habitat and provide for the annual production of SNS larvae. Thus, annual
production of larvae is not likely to be a limiting factor for SNS in Gerber Reservoir.
8.3.7.2 Effects to Gerber Reservoir Habitat for All SNS Life Stages
The effects of low water levels in Gerber Reservoir on SNS habitat use, population size, ageclass
distribution, recruitment, or decreased body condition are not fully understood. However,
available information (Barry et al. 2007c, Leeseberg et al. 2007) indicates that the Gerber
Reservoir SNS population has remained viable (i.e., shows evidence of regular recruitment and
high abundance) under the current management regime (USFWS 2008). Because the proposed
action is unchanged from past operations, low lake elevations resulting from Project operations
are unlikely to limit the persistence of SNS in Gerber Reservoir.
8.3.7.3 Effects to SNS in Gerber Reservoir as a Result of Water Quality
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
elevations because shallower depths would likely increase mixing of bottom waters and this
increase DO concentrations.
Blooms of blue-green algae can also reach densities in the fall and winter high enough to prompt
advisories by the State of Oregon, but it is unknown if these blooms are directly or indirectly
impacting SNS in this reservoir, or if Project operations affect the blooms.
The minimum proposed elevation for the end of September of 4,798.1 ft (1,462.5 m) in Gerber
Reservoir will likely provide adequate water depths for protection against winter kill of SNS,
which has apparently not occurred in the past during cold weather events where this elevation
was maintained (USFWS 2008).
Based on the stability of the SNS population in Geber Reservoir, and the fact that proposed
Project operations will be unchanged from past operations, adverse effects from water quality are
not likely to limit the persistence of SNS in Gerber Reservoir.
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