Our new Biological Assessment is out - Klamath Basin Crisis

Klamath Project Operations Biological Assessment
Endangered Suckers: Review of Proposed Action
lake elevation was at or greater than 4142.5 ft between 1995 and 2002, larval
production for size 15 mm total length was relatively low (1995, 1997, 1998,
2000, and 2005; Figure 2-23, Markle 2007).
In the other two years where June 15 lake elevation was above 4142.5 ft, larval
sucker abundances were the highest observed larval abundances in the 10-year
record presented. In years when mid-June lake elevation were below 4142.5 ft,
larval sucker production was low, but similar to larval abundances in 8 of the 10
study years, including years when mid-June elevation was higher than 4142.5 ft.
Markle (2007) indicates that larval sucker production, or year class formation,
appeared to respond to largescale climate indices and that the lake management
regime from 1995 to 2005 may have resulted in better year class formations under
different climate regimes.
Figure 2-23. UKL relationship between June 15 lake elevation (red x) and larval sucker
abundance for larvae of 15 mm total length (LPE15; blue square) from 1995 through
2005.
The relationship between larval year class formation and larval survival from
1995 to 2005 is also discussed in Markle and Dunsmoor (2007). A direct
relationship between larval abundance and lake elevation from the 1995 through
2005 data is difficult to ascertain since several years with high lake elevation also
had low larval sucker abundance (Figure 2-24). The authors indicate that larval
sucker survival may be related inversely to fathead minnow abundance (Markle
and Dunsmoor 2007). Lower lake elevations may favor fathead minnow
abundance and negatively influence larval sucker survival (Figure 2-24; Markle
and Dunsmoor 2007).
Also confounding the relationship between larval sucker abundance and lake level
management is the prevailing current in UKL that generally flows southerly along
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