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<br />c.) <br />C") <br />...... <br />co <br />1" <br />0') <br /> <br />decline in flannehnouthsuckerpopulations from 1991 to 1997, Ryden (2000a) suggested that this species <br />was in poor condition and poor health at the start of the study. This condition resulted from low-flow <br />drought periods during the late 1980s and early 1990s, and high population levels offlannehnouth sucker. <br />As research flows and higher natural streamflow occurred in the mid-1990s, the poorer-condition fish were <br />unable to survive, thus leaving a smaller but healthier population, This hypothesis suggests that flannehnouth <br />sucker population levels may be limited to some degree by health, and that when populations become too <br />large during low-flow periods, health issues caused by contaminants may be one factor that limits the <br />population. <br /> <br />Management Implications <br />The data collected in the San Juan River suggest that no special management is required for fish health <br />because it is not a limiting factor for the endangered fish species or for other native fishes, except perhaps <br />flannehnouth sucker, Incidence of abnormalities will continue to be recorded during monitoring, and if <br />abnormalities increase, adaptive management will allow for appropriate studies to be conducted, <br /> <br />CONTAMINANTS <br /> <br />Introduction <br />The effects of contaminants were considered a potential limiting factor to the endangered and other native <br />fishes in the Colorado River Basin (Holden and Stalnaker 1975, Seethaler et al. 1979). Human-caused <br />contamination from oil and gas development along the Green and San Juan rivers; uranium mining and <br />milling along the Green, Colorado, and Dolores rivers; and intensive irrigation along sections of almost all <br />Upper Basin rivers were of concern. Recently, the effects of naturally occurring selenium raised concern <br />because both natural and human-caused factors may concentrate this potential contaminant. These <br />concerns were evident as the 7-year research period and SJRIP were initiated, and several studies were <br />proposed to investigate this issue, <br /> <br />Abell (1994) sununarized the existing water quality information for the San Juan River and found that <br />existing information was not sufficient to determine potential effects on fish species. Wilson et al. (1995) <br />conducted a synoptic survey of inorganic contaminants of plants, invertebrates, and fishes throughout the <br />San Juan River, Additional studies on contaminants were conducted through 1996. Most of these studies <br />were sununarized by Simpson and Lusk (1999), who showed elevated concentrations of aluminum, arsenic, <br />copper, selenium, and zinc in various portions of the basin in different types of biota, but no clear link to <br />effects on native or endangered fishes was made, <br /> <br />The studies that showed potential significant contaminant levels in portions of the San Juan River <br />Basin prompted additional studies relating contaminant levels to problems for native and endangered <br />fishes. Of particular concern were effects on reproduction, the primary area where contaminants <br />were shown to affect fish populations. Three studies evaluating contaminant level effects on fishes <br />were funded by the SJRIP, and they were conducted by the U.S. Geological Survey, Hamilton and <br />BuhI (l997a) studied the effect of several individual inorganics (arsenate, copper, selenate, selenite, <br />zinc) and inorganic mixtures similar to those found in some irrigation <br /> <br />3-54 <br /> <br />Program Evaluation Report <br /> <br />September 2000 <br />