Laserfiche WebLink
Seicntlfle Pvaluatlon of Biological apinlons on Endangered and Th=trr1W T'IahCS In the Klamath Rivcr R&cin: Tntorim Rcport (2002) <br />hrt�mrwtu. nGp• UlWlrperN�nelrnrYNq,,] q7/ jIIMIN. 11u11I. cotyrl6hrZ1 11LZlral -JIM Narlr +pal&LWCraVnrSdCKMC.p11tltluar NLd <br />2. Evaluation of the Biological Opinion on <br />Shortnose and Lost River Suckers <br />Populations of the shortniose and Lost River suckers currently are present within <br />Upper Klamath Lake on the north side of the Klamath River drainage and within Clear <br />Lake (which operates as a reservoir) and Gerber Reservoir on the Lost River, to the <br />southeast (Figure 1). Small groups of individuals, some or all of which may be <br />nonreproducing. are found elsewhere in the Klamath River drainage, including Tule Lake <br />sump (USFWS 2001). Conditions in the lakes are relevant to the USFWS biological <br />opinion largely through proposals for minimum lake levels that are intended to reduce <br />mortality and improve spawning success, recruitment (addition of new individuals to the <br />population), growth, and condition of the suckers. <br />The population sizes of endangered suckers in Upper Klamath Lake and <br />elsewhere within the Klamath Basin are uncertain, but the abundances of these <br />populations, which orice were large enough to support commercial fisheries, are much <br />lower than they were when agricultural development and water management began. <br />Unfortunately, quantitative estimates of population sizes are not available. During the <br />1980s, qualitative evidence indicated that declines might have taken the sucker <br />populations in Upper Klamath Lake to just a few thousand old (> 10 years) individuals <br />(USFWS 1988). More recent estimates made possible incidentally by episodes of mass <br />mortality suggest, however, that the populations are considerably larger than they <br />appeared to be in the 1980s, and that some recruitment to the adult age classes has <br />occurred in most or all years of the last decade (see below). Population sizes may range <br />from a few tens of thousands to the low hundreds of thousands of individuals (USFWS <br />2001), but still are much lower than they were originally. Aside from decline in <br />abundance over the long term, other indications of problems within the sucker <br />populations include absence of spawning at a number of sites historically used for <br />spawning, apparent increase in mass mortality of adults ( "fish kills "), and weak <br />recruitment in most years (USFWS 2001). <br />The water quality of Upper Klamath Lake has changed substantially over the last <br />several decades. The lake appears to have been eutrophic (rich in nutrients and <br />supporting high abundances of suspended algae) prior to any anthropogenic influence <br />(Karm 1998). Mobilization of phosphorus from agriculture and other non -point sources <br />(Walker 2001), however, appears to have pushed the lake into an exaggerated state of <br />eutrophication that involves algal blooms reaching or approaching the theoretical <br />maximum abundances. >Tn addition, algal populations now are strongly dominated by the <br />single bluegreen algal species Aphanizomenon flos -aquae (Cyanobacteria) rather than <br />the diatom taxa that apparently dominated blooms prior to nutrient enrichment (Kann <br />1998, Eilers et al. 2001)_ <br />Evidence indicates that changes in the water quality of Upper Klatnath Lake have <br />increased mass mortality among adult suckers. Under certain conditions, the bottom <br />portion of the water column in the lake develops oxygen depletion and accumulates high <br />E <br />9136 -d 680MO'd 982 -1 8998998808 s dnosm lvdn1VN 100 -INOU ov:11 ZOOZ- 80 -93� <br />