Biological Opinions - Bureau of Reclamation

Figure 7.4 Modeled April through November deliveries to Project from UKL.
7.7.3 Effects of Historical Project Entrainment on the LRS and the SNS
The effects of entrainment on the LRS and the SNS caused by the Project have been described in
BiOps on proposed Project operations, the most recent BiOp being in 2008 (USFWS 2008, pages
72–76 and 127–135); that discussion is herein incorporated by reference. Entrainment causes the
largest quantified Project-caused loss of the LRS and the SNS, and is estimated to annually
involve millions of larvae and tens of thousands of juveniles (Gutermuth et al. 2000a, b, USFWS
2008). Entrainment of planktonic sucker larvae in UKL is thought to be related to drift and
wind-driven circulation patterns (USFWS 2008), but entrainment of juvenile suckers that are
more bottom-oriented is likely more complex and probably affected by multiple factors.
Juvenile suckers that are entrained at the A Canal and Link River Dam could be dispersing,
showing an avoidance response to poor habitat conditions, weakened by inhospitable conditions,
or a combination of these and other factors. Gutermuth et al. (2000a, b) found that entrainment
of suckers at the Link River was higher during poor water quality events, and thus leaving the
lake could be an avoidance response because fish tend to avoid unfavorable conditions such as
low DO or high water temperatures (Sullivan et al. 2003).
Prior to construction of the Link River Dam, sucker dispersal downstream into Lower Klamath
Lake was likely a natural part of the LRS’s and the SNS’s life cycle. However, now with the
higher summer flows at the outlet of UKL to meet irrigation deliveries and downstream riverflow
requirements, entrainment of age-0 juvenile suckers is likely greater than it was prior to
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