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Selentifie Tva.lunthn of'}iologlcnl ppinlohs on Lndangorcd and Throatoned Tliahcs In the Klamath Riwel' Rstaln: interim Ropnrr (2002) <br />rynC• rlaaa. �e�. Caumjcnnn�Wlurolnlev�i�h�mVtu .L�ml r��vvgphi 9W2. b1M111nc Na.l.�nol Ar.NemY m ;klcncec all Npum fmvca <br />ENDANGEx4EA ANA Tit6 A t FNEDFt IiES T1i KLAMATFI J tYER BAS 1n <br />concentrations of ammonia_ Mixture of these bottom waters with the surface waters <br />under the influence of changes in weather is the likely cause of mass mortality (Vogel et <br />al. 2001, Home 2001). While crass mortality has been recorded over the entire observed <br />history of the lake, its frequency appears to have increased (Perkins et al. 2000). Major <br />incidents were recorded for years 1995, 1996, and 1997; low dissolved oxygen appears to <br />have been the direct cause of mortality in these years (Perkins et al. 2000). <br />Impairment of water quality also may stress fry through the creation of high pH in <br />surface waters as a result of high rates of photosynthesis, although exposures to the <br />highest pH probably are too brief to cause mortality (SaW et al. 1999). In addition. the <br />present trophic state of the lake potentially poses a threat of mortality in winter, when <br />anoxia can occur under ice if oxygen demand is high. Although not yet observed, winter <br />mortality could occur in the future (Welch and Burke 2001). <br />Factors of concern other than water quality include the presence of exotic species <br />capable of inducing types of predation and competition that are foreign in an evolutionary <br />sense to these endemic species. Hybridization occurs but the degree of threat associated <br />with it is unknown; the native suckers probably showed some interbreeding prior to <br />human intervention (Markle et al. 2000). In addition, access of the suckers to historically <br />significant spawning areas has in many cases been blocked or the spawning areas <br />themselves have been physically degraded to such an extent that they cannot serve their <br />former roles (USFWS 2001). Overfishing or habitat degradation may have eliminated <br />portions of the population that were using specific spawning areas and, although fishing <br />no longer occurs, these subpopulations cannot be regenerated without manipulation of <br />existing stocks in combination with habitat restoration. <br />Suckers of all sizes are entrained by water management structures (USFWS <br />2001). While screening of these structures has long been recognized as an important <br />means of reducing mortality of the endangered suckers, it has not yet been accomplished. <br />Also, interaction of multiple stresses may increase vulnerability of the endangered <br />suckers to disease, degrade their body condition, and cause them to show a high <br />incidence of anatomical abnormalities (Plunkett and Snyder -Conn 2000). <br />The USFWS biological opinion states that the Klamath Project is detrimental to <br />the endangered suckers through its direct contributions to mortality and adverse <br />environmental conditions_ On this basis, USFWS presents a reasonable and prudent <br />alternative MA) consisting, in summary, of requirements for rainimum lake levels, <br />coordination and adaptive management, screening to prevent entrainment of fish, creation <br />of improved passage facilities, steps toward improvement of habitat and water quality, <br />and additional studies. The RPA is intended to avoid jeopardizing listed species either <br />dixectly or through adverse modification of critical habitat (50 CFR 402.02). <br />With the exception of the recommendation on lake -level maintenance, there is <br />good scientific or technical support for all of the requirements listed in the RPA. <br />Coordination and adaptation of management are advisable, especially because the <br />information base is evolving rapidly and because annual optimization of strategies for <br />using water is an obvious need. Given the documented loss of suckers to entrainment and <br />the blockage of their access to spawning waters at known locations (USFWS 2001), <br />requirements of the RPA calling for mitigation of these problems also seems highly <br />defensible. Potential for improvement of habitat and water quality must be viewed as <br />incremental rather than comprehensive, but even incremental improvements offer the <br />10 <br />966 -d 880 /EZO•d 9EZ -1 899E998E0E s3oNnosm 1vNn1VN 100 -NONd IV: H ZOOZ- 80 -93d <br />