Biological Opinions - Bureau of Reclamation

8.3.7.4 Effects of Entrainment Losses of SNS at Gerber Reservoir
Past efforts to quantify entrainment or salvage-stranded suckers in Miller Creek downstream
from Gerber Dam as a result of Project operations suggest that several hundred age-0 and older
juvenile suckers are annually entrained at the dam as result of Project operations (Hamilton et al.
2003). Based on the quantities of water delivered in the past decade and the proposed action,
Reclamation assumed several hundred age-0 and older juvenile suckers will be annually
entrained under the proposed action (USBR 2012). Larval and age-0 juvenile suckers are also
likely entrained, but this has not been studied.
The proposed action includes opening of Gerber Dam frost valves at the end of the irrigation
season that, which allows for a flow of approximately 5 cfs (0.1 m 3 /sec) in Miller Creek.
Downstream accretions from seeps and storm runoff increase the actual instream flow within
Miller Creek. This flow may still not be sufficient to allow for stream pool connectivity (USBR
2012) and consequently some suckers are likely to be stranded stream pools and die at the end of
the irrigation season.
There is likely to be entrainment losses of larval, juvenile and adult suckers as a result of the
proposed action at Gerber Reservoir. However, available information (Barry et al. 2009, 2007a,
Leeseberg et al. 2007) indicates that the Gerber Reservoir SNS population has remained
moderately large and has frequent recruitment under the current management regime, and so we
anticipate this will continue under the proposed action. Thus, levels of entrainment that are
likely to occur with implementation of the proposed action and the resulting adverse effects to
SNS are unlikely to occur at a level that limits the persistence of SNS in Gerber Reservoir.
Summary of Effects to LRSs and SNSs in the Gerber Reservoir
Based on the analysis presented above, the USFWS concludes that most of the biological effects
of the proposed action to SNS in Gerber Reservoir are likely to be compatible with the
conservation needs of the SNS. Entrainment is likely to be the most significant adverse effect,
but because the SNS population has remained viable with current levels of entrainment, and
operations is not anticipated to change, adverse effects are unlikely to occur at a level that limits
the persistence of SNS in Geber Reservoir.
8.3.8 Effects to the LRS and the SNS in Tule Lake Sump 1A
Tule Lake consists of two sumps: Sump 1A (9,000 ac [3,642 ha]) and Sump 1B (4,000 ac [1,619
ha]). There is a small population of the LRS and the SNS located in Sump 1A. Only, a few
suckers have ever been documented in Sump 1B, despite the fact that there is access to Sump 1B
from 1A (Freitas et al. 2007). It is unknown why suckers do not inhabit Sump 1B, but in an
effort to better understand this situation, 18 radio-tagged suckers were experimentally put into
Sump 1B in 2011 to assess their movements and survival. All, of these suckers returned to Sump
1A when access became available in 2012, confirming that, for unknown reasons, suckers prefer
Sump 1A.
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