Laserfiche WebLink
<br />GJ2<t83 <br /> <br />centrarchid fishes was not appreciated. Langhorst and Marsh (1986) found that <br />razorback sucker larvae were only distinguishable in stomachs of green sunfish <br />(Lepomis cyanellus) for about 30 minutes. After that time the larva essentially were <br />dissolved. <br /> <br />Negative interactions with introduced fishes also have been well documented for <br />some Colorado River basin fish species that occupy smaller habitats. Meffe (1985) <br />demonstrated that direct predation on juvenile topminnows (Poeciliopsis occidentalis) <br />by an introduced mosquitofish (Gambusia affinis) was the primary means for species <br />replacement. Another introduced mosquitofish (G. holbrookl) exerted significant <br />negative effects on the abundance of the least killifish (Heterandria formosa), and only <br />complete removal of the predator reversed the effect (Lydeard and Belk 1993). In <br />another investigation, Deacon (1978) documented competitive interactions between <br />introduced goldfish and Pahrump killifish (Empetrichthys latos latos). <br /> <br />There are less obvious, but nonetheless potentially important adverse <br />interactions that do not involve predation by non natives. Colorado squawfish are <br />known to prey on channel catfish, but may choke on the catfish's spines (Vanicek 1967, <br />MeAda 1983, Pimental et al. 1985, Quaterone 1993). Hybridization of white suckers <br />with other native Colorado River suckers has been reported and could compromise the <br />genetic integrity of the native fishes (Burdick 1995). <br /> <br />The body of evidence documenting the deleterious effect of nonnatives on the <br />native fishes of the Colorado River system is sufficiently compelling to have convinced <br />most experts in the region. Hawkins and Nesler (1991) polled regional fisheries <br />experts and found that 81 % believed nonnative fishes were responsible for significant <br />problems in the UCRB. Maddux et al. (1993) reviewed issues related to the recovery of <br />the four endangered big river fishes and found that interactions with non natives were <br />the primary factor limiting recovery in some areas. Lentsch et al. (1995) identified the <br />nature of negative interactions of many non natives with the endangered species. The <br />nonnative fish issue has been studied thoroughly and we believe the conclusion is <br />inescapable that introduced species have played a significant role in the decline of the <br />native big river fishes, and continue to adversely effect the native fishes and their <br />habitats. <br /> <br />The adverse effects that nonnatives have on the native species makes the <br />natives "more susceptible to extinction by chance, catastrophe, and habitat alteration" <br />(Frankel and Soule 1981). Whereas competition and predation would not be regarded <br />as major forces for extinction of continental biota, they could be significant factors for <br />small populations of an insular fauna (Frankel and Soule 1981, Raup 1991). The <br />endangered fishes of the UCRB have already been described as part of an insular <br />fauna, and the extant populations are small and isolated. It is therefore an appropriate <br />and necessary that the UCRB fauna be viewed in the context of present theories <br /> <br />11 <br />