Biological Opinions - Bureau of Reclamation

7.10.3.3 Competition and Predation by Nonnative Fishes
Historically, the LRS and the SNS co-occurred with at least 10 native fishes, which potentially
interacted with the suckers as predators or competitors. Now, the Upper Klamath Basin fauna
includes 20 nonnative fishes, many of which comprise a significant portion of the fish
community (Scoppettone and Vinyard 1991). The nonnative fish species most likely to
adversely affect the LRS and the SNS are the fathead minnow and yellow perch. These fishes
are believed to prey on young suckers and compete with them for food or space (Markle and
Dunsmoor 2007); although, specifics are unavailable. Given the very high abundances of
fathead minnow known to occur in UKL, Lake Ewauna, and other areas, this interaction may be
significant for early life stages of the LRS and the SNS.
7.10.3.4 Entrainment of LRS and SNS at the Outlet of UKL
Suckers of all life-stages are entrained at the Link River Dam and larval suckers are entrained at
the A canal, both located at the outlet of UKL. The effects of entrainment on LRS and SNS have
been described in previous consultations, the most recent being in 2008 (USFWS 2008, pages
72-76 and 127-135). Because that topic has been covered recently, we incorporate that
information by reference. Entrainment causes the largest quantified loss of LRS and SNS and is
estimated to involve millions of larvae and tens of thousands of juveniles (Gutermuth et al. 2000;
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 is 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, 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).
Entrainment is more likely to occur now, compared to the pre-Project condition, because when
Link River Dam was constructed, deep channels were cut through the reefs at the outlet of the
lake (USBR 2001a). The reef closest to the lake was located at Putnam’s Point. The historical
reef had a minimum elevation of approximately 4,137 ft (1,261 m), although most of the
historical reef surface was at 4,140 ft (1,262 m), thus restricting downstream flows at this
elevation (USBR, unpublished data). When the Link River Dam was built, it was determined
that raising the lake more than a few feet would not be possible because of the risk it posed to
existing dikes around the lake. Therefore, in order to maintain a sufficient water supply for
agriculture, plans were put in place to lower the lake below its normal 2 ft (less than 1 m) range.
In1921, to allow for lake levels to be drawn lower and to increase channel capacity, a cut about 8
ft (2.4 m) deep and 100 ft (30 m) wide was made through the upper reef near Putnam’s Point to
an elevation of 4,131 ft (1,259 m; Boyle 1987). Downstream, a second reef located above the
current dam had a low point at 4,137 ft (1,261 m), but most of the cross-sectional area was at an
elevation of about 4,139 ft (1,262 m). Two cuts were made in this reef near the ends of the dam
to increase flow and enable the lake to be lowered. The pre-Project water depths over both reefs
mostly would have been only 1 to 2 ft (less than 1 m) in August and September when juveniles
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