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1950's (see Quarterone 1993) likely boosted mortality rates, though harvest by aborigines <br />during seasons when the fish were concentrated may also have been significant during <br />prehistoric times. Anglers today fish for the introduced channel catfish (Ictaluras punctatus), <br />but mortality from incidental catches of Colorado squawfish still occur, particularly in the <br />Grand Valley where the river is surrounded by an urban area (FWS unpublished data). <br />Trammel et al. (1996) conducted creel surveys along portions of the Colorado River in Utah <br />and concluded that angling-related mortality of Colorado squawfish there was probably <br />insignificant. While the significance of angler-related mortality in the Grand Valley is <br />unknown, it has probably been greatly reduced during the past 20 years from educational <br />efforts and the penalties associated with harming a protected species. <br />New mortality factors to which Colorado squawfish may be subjected include parasitic <br />diseases and problems encountered with ingestion of channel catfish. While some parasitic <br />diseases have been introduced, none are believed fatal (Seethaler 1978, Flagg 1982) and little <br />additional mortality would be expected. Numerous fishermen have reported finding dead <br />Colorado squawfish containing channel catfish with the spines extended and lodged in the <br />pharynx or esophagus (Vanicek and Kramer 1969, Quarterone 1994). The probability of <br />encountering any dead squawfish is very low; the fact that several have been reported with <br />catfish in their throats suggests this is not an uncommon occurrence. McAda (1983) and <br />Pimentel et al. (1985) reported extracting channel catfish from the mouths of live Colorado <br />squawfish. During our study, several large Colorado squawfish were observed with <br />perforations or slits in the gular region, suggesting past encounters with the spines of ingested <br />channel catfish. Because channel catfish are abundant and ubiquitous, the likelihood of a <br />long-lived piscivore eventually eating one is probably high; consequently, we suspect this is a <br />significant source of mortality. <br />Gilpin's (1993) population viability analysis (PVA) on the Green River population of <br />Colorado squawfish identified information gaps that if filled would strengthen future PVA or <br />other population assessments dependent on demographic analysis. Growth and survival rates <br />were important parameters for which he identified the need for more accurate estimates. This <br />work is a step toward fulfilling that need. <br />A-19