Our new Biological Assessment is out - Klamath Basin Crisis

Klamath Project Operations Biological Assessment
Endangered Suckers: Environmental Baseline for Suckers
voluntary closure of the tribal fisheries by the Klamath Tribes in 1986 and the
State closure of the sport fishery in 1987.
E. Summer Fish Die Off Events
Fish die-off events in the 1990s are reflected in the length frequency distributions
of suckers in UKL. In addition to the die off events of the 1990s, a small number
of dead and moribund adult suckers were recovered in 2003 (Foott 2004).
Water quality in UKL consistently reaches levels known to be stressful to suckers
and periodically reaches lethal levels in August and September, resulting in dieoffs
(USFWS 2002). Fish die-offs have been recorded at UKL since the late
1800s but may have increased in frequency in the last few decades. Small,
localized fish die-offs have been observed annually on UKL since 1992 when
extensive research and monitoring activities began (USFWS 2002). In 1995,
1996 and 1997 a series of major fish die-offs in UKL reduced adult sucker
populations of Lost River and shortnose suckers UKL by an estimated 80-90
percent (USFWS 2002). Adult sucker die-offs in the 1990s were likely caused by
stressful and lethal water quality conditions. Perkins et al. (2000 Water Quality)
reported that some adult suckers died several weeks after critically low DO
concentrations were observed during the 1990s fish die offs. For further
discussion on Upper Klamath Basin water quality see Environmental Baseline
section titled Water Quality in the UKL watershed.
The delay between dying adult suckers and critically low water quality parameters
implicates that fish health, such as infection by pathogens or parasites, is a factor
during die off events. The extent of a 2003 fish die-off in UKL is unknown,
however, only small numbers of dead adult suckers were recovered (Foott 2004).
Dead and moribund suckers recovered during the 2003 fish die-off were infected
with several pathogens and parasites (Foott 2004). Fish die-offs of the 1990s may
have also been, in part, a result of parasite and pathogen infections in fish as adult
suckers were observed dying in the weeks that followed critically low DO events
(Perkins et al. 2000 Water Quality).
Disease and parasite prevalence were not identified as threats at the time of listing
for either suckers species. However, information since 1988 indicates that
pathogens and parasites affect sucker health and survival, especially during
adverse water quality events (USFWS 2007 LRS, 2007 SNS). Fish susceptibility
to parasite and pathogen infections in the Upper Klamath Basin may, in part, be
increased by stressful water quality conditions.
Adverse water quality conditions in Clear Lake and Gerber Reservoirs is
primarily determined by shallow reservoir depths, which reduce available habitat
and cause declines in DO. Results of fish crowding into reduced habitat and
reduced available DO can stress suckers and reduce individual fitness. Available
habitat in Tule Lake is severely limited by shallow depths and further limited by
seasonal declines in water quality. All three water bodies (UKL and both Clear
87