Scientific Evaluation of Biological Opinions on Endangered and Threatened Fishes in the Klamath River Basin Interim Report (2002) / Chapter Skim
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2 Evaluation of the Biological Opinion on Shortnose and Lost River Suckers
2 Evaluation of the Biological Opinion on Shortnose and Lost River Suckers
Pages 11-20
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From page 11... ...
The population sizes of endangered suckers in Upper Klamath Lake and elsewhere within the Klamath Basin are uncertain, but the abundances ofthese populations, which once were large enough to support commercial fisheries, are much lower than they were when agricultural development and water management began. Unfortunately, quantitative estimates of population sizes are not available.
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From page 12... ...
12 Endangered and Threatened Fishes in the Klamath River Basin
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From page 13... ...
consisting, in summary, of requirements for minimum lake levels, interagency coordination and adaptive management, screening to prevent entrainment of fish, creation of improved passage facilities, steps toward improvement of habitat and water quality, and additional studies. The RPA is intended to avoid jeopardizing listed species either directly or through adverse modification of critical habitat (50 CFR 402.021.
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From page 14... ...
_ _ :. ~ ~~ cot 0 c, no :: ~ ~~ ~:'ct- | Nova · Dry Water Years' USBR proposed o Critical Dry Water Years, USBR proposed Mean, 5 Dry Water Years, 1960~1998 ——Mean, 2 Critical Dry Water Years, 1960~1998 ~ USFWS Biological Opinion FIGURE 2 Overview of monthlylevels for Upper Klamath Lake proposed byUSBR through its biological assessment of 2001, USFWS through its biological opinion of 2001, and observed conditions for the years 1960-1998.
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From page 15... ...
The USBR proposed minimums are below the mean lake levels for the historical operating regime in each of the two dry-year categories, because the USBR used the lowest recorded monthly lake levels as its proposed minimums for each category. The USBR proposal would allow more drawdown of lake level than has been characteristic in the past.
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From page 16... ...
As indicated above, the present scientific evidence for this association is credible. An essential premise of the lake-level recommendations is that the adverse water-quaTity conditions known to stress or kill the endangered suckers are associated with the lowest water levels within the recent historical range of levels (since 1990, when consistent documentation first began)
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From page 17... ...
Thus, the idea of relieving eutrophication through phosphorus dilution caused by higher lake levels is not consistent with the irregular relationship between chlorophyll and lake level. Also, lake level fails to show any quantifiable association with extremes of dissolved oxygen or pH (see data presentedby Welch and Burke 2001~.
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From page 18... ...
casts doubt on the importance ofthis factor, at least within the operating range of the ~ 990s. Overall, the presumed causal connections between lake levels and recruitment ofthe sucker populations in Upper Klamath Lake do not have strong scientific support at present.
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From page 19... ...
Despite a monitoring record of substantial length, there is no clear evidence of a connection between the lake levels and the welfare of the two sucker species in Upper Klamath Lake. Lake levels cannot be reduced, how
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From page 20... ...
The potential benefits of higher lake levels in Clear Lake, Gerber Reservoir, and Tule Lake sump are more difficult to evaluate, because the record of analysis and observation for these water bodies is not as extensive as that for Upper Klamath Lake. These lakes have not suffered notable mass mortality in association with low lake levels, but Clear Lake populations showed poor body condition following severe drawdown in the early ~ 990s.
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