Biological Opinions - Bureau of Reclamation

were present; now depths are 7 to 9 ft (less than 3 m) in the cuts. The shallow depths over much
of the reefs likely reduced downstream movement of juvenile and adult suckers from UKL, but
may have had no effect on larvae, which are weaker swimmers and surface oriented.
Hydraulic surveys made during July and September 1998 measured current velocities of up to 2
cfs (0.06 m 3 /sec) in the area of the Link River upstream from the A Canal (Wahl and Vermeyen
1998; USFWS 2008, Figure 4-6). These flows are about twice the 1 ft/s (0.3 m/s) critical
swimming speed (or approximately five body lengths per second) for age-0 juvenile suckers
about 2.4 in (6 cm) in length (Delonay and Little 1997, Sechrist and Sutphin 2011), thus once
small suckers get into the upper Link River above the dam, many, if not most, are likely swept
downstream to the dam and then into the Keno Reservoir. We have no data regarding the current
velocities prior to construction of the deep channels through the natural reef at the outlet of UKL.
However, as noted above, the natural structure and elevation of this reef likely limited natural
downstream migration of juvenile and adult suckers.
Based on studies at the outlet of UKL, most age-0 juvenile sucker losses from the lake that result
from emigration and entrainment at the UKL outlet occur in July through October, with a peak in
August and September (Gutermuth et al. 2000a, b; Foster and Bennetts 2006; Tyler 2007;
Korson et al. 2011; Korson and Kyger 2012).
As a natural part of sucker life history in UKL, young suckers likely dispersed downstream from
UKL to rear in Lower Klamath Lake and then returned to UKL as adults. That cycle was broken
when access to Lower Klamath Lake was blocked by the construction of the railroad
embankment in the early 1900s (Weddell 2000, Foster 2002). Further disruption of the dispersal
patter from UKL to Lower Klamath occurred with the construction of the Link River Dam in the
early 1920s. Now, most suckers that are entrained at the Link River Dam are considered lost to
the breeding populations in UKL (USFWS 2007c, 2008); although, small numbers of adults
annually return to UKL via the new fish ladder (Kyger and Wilkens 2010a).
Larval and juvenile survival in Keno Reservoir is low, probably due to the poor water quality
and degradation, as described above, and loss of lake and wetland habitat due to agriculture
conversion, railway construction, and near constant water level management (USFWS 2007c,
2008). Adult suckers in Keno Reservoir appear to avoid adverse water quality in the reservoir by
moving into the Link River (Piaskowski 2003); they can re-enter UKL via the new fish ladder,
but it is unknown to what extent smaller suckers are able to avoid adverse conditions in the Keno
Reservoir so that they can survive and recruit into the adult population. Juvenile suckers are
known to use marshes in Keno Reservoir; in 2010, Reclamation biologists captured 70 age-0
juvenile suckers in the largest remaining marsh, Tule Smoke (Phillips et al. 2011). However,
because DO levels reached potentially lethal concentrations below 2 mg/L numerous times
during the study, it is doubtful that this habitat consistently provides conditions necessary for
sucker survival under current conditions.
7.10.4 Synergistic Effects of Water Quality, Parasites, Predation, Disease, and
Entrainment on Juvenile Suckers in UKL
The available information discussed above suggest that a mid-to-late summer cascading series of
events are likely responsible, in part, for the disappearance of age-0 juvenile suckers in UKL.
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