Our new Biological Assessment is out - Klamath Basin Crisis

Klamath Project Operations Biological Assessment
Endangered Suckers: Sucker Description, Life History, Habitat, Distribution, and
Abundance
investigations of juvenile suckers in UKL have each indicated a different
dominant substrate where juvenile suckers have been observed in unvegetated
nearshore areas: mud and sand (Buettner and Scoppettone 1990), gravel and
cobble (Simon et al. 2000, Terwilliger et al. 2004, Terwilliger 2006), and sand,
fines, gravel, intermixed substrates and cobble (Hendrixson et al. 2007a, 2007b).
In late summer and early fall, YOY juveniles continue to occupy shoreline areas
of UKL with evidence of a habitat transition into offshore areas during autumn
(Terwilliger 2006). There is also substantial evidence that suggests emergent
vegetation may also provide important habitat for juvenile suckers (Reiser et al.
2001, VanderKooi and Beulow 2003, VanderKooi et al. 2006, Hendrixson et al.
2007a, 2007b).
In mid-summer, juveniles are concentrated in the northern and eastern sections of
UKL, near the mouth of the Williamson River and along the eastern shoreline. In
late summer and fall most juveniles are concentrated in the south end of UKL and
along the eastern shoreline (Simon et al. 2000, Simon and Markle 2001,
Terwilliger et al. 2004, Hendrixson et al. 2007a, 2007b). Rocky bottoms occur
along the shoreline primarily in the southern portion of UKL while emergent
shoreline vegetation occurs primarily in the northern half of the lake, and soft,
mucky bottoms occupy the vast majority of the deeper offshore areas.
Juvenile sucker abundance drops dramatically from August to October in UKL
(Simon and Markle 2001, Terwilliger et al. 2004, Terwilliger 2006). Catches of
juveniles in emergent vegetation also declined significantly near the end of
August in both 2000 and 2001 (VanderKooi and Beulow 2003, VanderKooi et al.
2006). However, the cause for declining juvenile sucker abundance in late
summer and early autumn is undetermined. Possible hypotheses explaining the
apparent reduced abundance of juvenile suckers include reduction of emergent
vegetation habitat with reducing lake elevation (VanderKooi and Beulow 2003,
Markle and Dunsmoor 2007), a shift to offshore habitat use (Terwilliger 2006),
and emigration from UKL (Markle et al. 2007 Juvenile).
There is evidence that sucker emigration from UKL into the Link River, including
the east and west power canals that parallel the Link River, increases during the
period between July and October at the south end of the lake (Gutermuth et al.
1999, 2000, Foster and Bennetts 2006, Tyler 2007). The cause of emigration by
juvenile suckers is not currently understood. Plausible hypotheses include natural
emigration, avoidance of poor water quality events, and diminished habitat in the
north end of UKL which concentrates suckers in the southern end of UKL near
the outlet (USFWS 2002). The fate of emigrant suckers is not fully understood
but it has been hypothesized that UKL is a better environment for suckers due to
its food rich environment, the loss of connectivity between habitats below the
Link River, and frequent poor water quality events in the Link to Keno reach of
the Klamath River (Reithel 2006).
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