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<br />mixture of species in the Gunnison River at Delta. A few trout were observed <br />in the Gunnison River at Delta and at the wildlife area. The fish species <br />most frequently observed in the Uncompahgre River at Colona were trout, <br />suckers, and mottled sculpin. Carp, suckers, and roundtail chub were the most <br />frequently observed species in the Uncompahgre River at Delta. <br /> <br />Two river otters (a mother with her young) were observed along the <br />Gunnison River near the Escalante State Wildlife Area. Historically, otters <br />were native to the study area, and the Colorado Division of Wildlife considers <br />the otters a threatened species and is attempting to reintroduce otters in the <br />Gunnison River basin. River otters have been reintroduced in the Black Canyon <br />of the Gunnison River, which is the reach immediately downstream from the <br />Gunnison Tunnel diversion (near gaging station 09128000 in fig. 1 or site 2 in <br />fig. 2). It is not known where the otters at the Escalante State Wildlife <br />Area originated. <br /> <br />Data Interpretation <br /> <br />Many chemical, physical, biological, and physiological factors affect <br />the toxicity of environmental contaminants to biological organisms. Chemical <br />and physical factors include contaminant type, chemical species or form, water <br />temperature, hardness, pH, dissolved oxygen, salinity, and multiple-chemical <br />exposure (antagonism and synergism). Also affecting toxicity are duration of <br />exposure, quantity of contaminant, and pathways of the contaminant from the <br />environment into the organism. Depending on concentration, the effects can <br />be beneficial to the organism, have subtle biochemical changes, or be lethal. <br />Biological and physiological factors affecting toxicity include species, age, <br />sex, and physiological state of the organism. Interpretation of contaminant <br />concentrations in biota is difficult, complex, and in many instances, may not <br />be possible using data collected from field studies. One of the best methods <br />for interpretating contaminant data is by comparison with data collected from <br />other field studies and laboratory studies. <br /> <br />Concentrations of inorganic trace elements in biological samples are <br />extremely variable. Such data can be interpreted by comparison to available <br />literature to determine if concentrations exceed background concentrations <br />or exceed concentrations that may be harmful to fish and wildlife. One of <br />the most frequently used literature sources is the National Contaminant <br />Biomonitoring Program (NCBP) of the U.S. Fish and Wildlife Service. Lowe and <br />others (1985) reported the 85th-percentile concentration for arsenic, cadmium, <br />copper, lead, mercury, selenium, and zinc for fish samples collected in <br />1980-81 throughout the United States. The 85th percentile has been estab- <br />lished by NCBP as an arbitrary concentration for distinguishing whole-body <br />fish samples that have large concentrations of the seven trace elements. The <br />85th percentile has no meaning with respect to potential hazards to fishery <br />resources or to regulatory statutes. The 85th-percentile concentrations in <br />Lowe and others (1985) were reported as wet-weight concentrations. For ease <br />of comparison with the biota data listed in tables 20 through 23, which are <br />dry-weight concentrations, the wet-weight concentrations reported by Lowe <br />and others (1985) were converted to dry-weight concentrations by assuming an <br />average moisture content of 75 percent. Fish samples collected for this <br />reconnaissance had moisture contents ranging from 61 to 84 percent; therefore, <br /> <br />50 <br />