Committee on Resources - Hornady-Marshall Auditorium College Park

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Sciondfic rvaluation of Biological Opinions on rndangercd and Threatenod T'lshcsu in the Klarnnth River Basin• lnterhn Report (2002) nrtr:me�w.nan•ce�Wq eeh��kAn�r�U�9ZN��x n via.neTi, [tryMgh� ZA2. n.0 The NwV-na1 neL1cmv V Sc�uccr, Meow rmmm EVALUATION OF THE BiOIOG CAL OPINION ON SHOIt1Tto3ig AND LOURW-M SIX 7KERS reflect seasonality that is partly inherent in the runoff reaching Upper Klamath Lake and partly a byproduct of water withdrawals. The degree of seasonality in the USFWS RPA is considerably lower, however, than the seasonality of the other two regimes depicted in Figure 2, and minimum levels are highest overall for the USFWS RPA. The USBR proposed minima are below the means for the historic operating regime in each of the two dry -year categories because the USBR used the lowest recorded monthly lake levels for each category as its proposed,minima. From the viewpoint of lake levels, water years are almost independent of each other because the lake has little capacity for interannual storage. The USBR proposal would allow more drawdown of lake level than has been characteristic in the past. Although the take levels proposed by USBR have been observed over the last 40 years, the use of these 40 -year minima as year -to -year minima indicates that drawdown to the 40 -year minima would be possible in any year of future operations if USBR's proposals were accepted. If USBR chose to operate the project by using greater average drawdown than has been observed over the past 40 years, the result would be significantly lower mean lakc levels in each of the hydrologic categories. Control of lake levels as a means of advancing the welfare of the endangered suckers raises more difficult scientific issues than the other requirements listed by the USFWS in its RPA. The recommendation for water -level control is based on concerns related to habitat (shoreline spawning areas, emergent vcgetation), and water quality (low oxygen in summer, need for deep water refugia in summer and fall, possibility of adverse conditions der ice cover). Imp a ent of water quality, primarily through eutrophication of Upper Klamath Lake, is a c use of mortality and stress for sucker populations. As indicated above, the present scientific evidence for this association is credible. An essential premise of the lake -level recommendations, however, is that the adverse water quality 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). Presumption of this connection, which is essential to the arguments for specific lake levels that are proposed in the RPA, is inconsistent with present information on Upper Klamath Lake. Control of phosphorus in Upper Klamath Lake offers the potential of suppressing population densities of algae, thus improving water quality in the lake (Welch and Burke 2001). No relationship between lake levels and population densities of algae (as shown by chlorophyll) is evident, however, in the nine -year water - quality monitoring record that has been fully analyzed (Figure 4). 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 presented by Welch and Burke 2001). For example, the most extreme pH conditions recorded for the lake over the last ten years came in 1995 and 1996, which were years of intermediate water level, and not with years 1992 and 1994, when water levels were lowest (these two years had the lowest recorded water levels since 1950). Furthermore, a substantial mass mortality occurred in 1971, the year of highest recorded water levels since 1950 (USFWS 2001) and, within the last ten years, mortality of adults was highest in 1995, 1996, and 1997, notle of which was a year of low water level, The absence of notable adult 13 966 -d BEOMO'd 96Z -1 899899BEOE snnosu 1Vanm 100 -1N0ad ZV:11 ZOOZ- 80 -83d