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<br />OfJ2528 <br /> <br />4.1 Native Fish Fauna Characteristics <br /> <br /> <br />particularly those o{state agencies ~d c6nsuIting fIrms, were contacted by telephone for information. In <br />several cases the authors of unpublished material have asked that it not be included until it has been <br />approved and published. <br />This review was compiled beginning in F ebrumy 1993 and includes studies, reviews, data sets, <br />and communications available by July 1, 1993. All information gathered for the review is archived at the <br />New Mexico Ecological Services Office of the U.S. Fish and Wildlife Service. All future inquiries <br />regarding the review should be directed to the contaminants specialist at that office. <br /> <br />4. RESULTS <br /> <br />4.1 NATIVE FISH FAUNA CHARACTERISTICS <br /> <br />The San Juan basin native fish fauna, as a result of their life histories, physiologies, and habitat <br />preferences, are in certain ways particularly vulnerable to contaminants and the snite of water quality <br />changes that have occurred in the basin. <br />The native fishes rely heavily on backwater areas and low-flow channels as habitat for larvae, <br />young-of-the-year (YOY), and juveniles, and it is in these areas that contaminants tend to concentrate, <br />especially if a contaminant enters the system as a surface water input (petty et al. 1992). In the Upper <br />Colorado River basin, Colorado squawfish occur in a variety of habitats, but YOY, juveniles, and <br />subadults prefer quiet backwaters with little or no current (Seethaler 1978, Tyus et al. 1982, Tyus 1987). <br />Tyus (1991) found that young squawfish moved in and out of backwaters as temperatures fluctuated, <br />locating the wannest water. SubaduIt and adult Colorado squawfish were also found in backwaters, <br />although they did not rely on them exclusively (Seethaler 1978, Meneely et al. 1979). During peak runoff, <br />adults have been observed to move to backwaters where there were wanner temperatures (Colorado Fishes <br />RecovCty Team 1991). Likewise, adult roundtail chub have been found in a variety of habitats and have <br />seemed to prefer deeper pools of large streams, but larvae of the species have preferred backwaters for their <br />habitat (Meneely et al. 1979, Petty et al. 1992). Razorback sucker have been found to prefer backwaters <br />of rivers or impounded waters (Holden and Stalnaker 1975). Like the Colorado squawfish and roundtail <br />chub, razorback sucker larvae depend on backwaters, with older fish showing a preference for backwaters <br />of rivers or impounded waters. Young bluehead and flannehnouth suckers have also been found in <br />backwaters associated with main channels (Meneelyet al. 1979). <br />When contaminants concentrate in backwater habitats, fish inhabiting them are exposed to the <br />contaminants through several pathways. If adult fish move into the nursery areas prior to reproduction, <br />they may ingest food items in which contaminants have already accumulated to greater than background <br />concentrations (National Fisheries Contaminant Research Center et al. 1991). Adult fish may then transfer <br />accumulated levels of contaminants to their offspring. Larval, YOY, and juvenile fish may also accumulate <br />contaminants by direct uptake from the water or through feeding. In Colorado squawfish and razorback <br />sucker, for whom critical life stages are from fertilized eggs through the first year (Miller et al. 1982), <br />increased exposure to contaminants in back-waters has the potential to reduce reproductive success <br />(National Fisheries Contaminant Research Center et al. 1991). Evidence from recent larval fish studies <br />has shown that, at least for the Colorado squawfish, recruitment of young is exceptionally low (platania <br />1991). <br />The endangered fishes of the basin are also at high risk of contamination as a result of their life <br />history strategies. Colorado squawfish and razorback sucker are long-lived, require several years to reach <br />sexual maturity, and may reproduce infrequently after reaching maturity (Seethaler et a1. 1979, Roy and <br />Hamilton 1992). The females of these species carry their eggs and precursor materials for years before <br />shedding them during spawning, allowing an extended period of time for contaminant accumulation in the <br />ovaries and eggs (Roy and Hamilton 1992). As predaceous piscivores, Colorado squawfish face the <br />additional risk ofbiomagnification of contaminants (Seethaler et al. 1979). <br /> <br /> <br />15 <br />