7970 - Laserfiche WebLink

Home Browse Search

Introduction Many freshwater fishes native to the North American West are threatened with extinction, largely due to human influences (reviewed in Minckley and Deacon, 1991). Water management practices have reduced and extensively modified aquatic habitats and their surrounding landscapes, and non-native species, usually introduced as sport- or baitfish have seriously affected indigenous species through competition, predation, and hybridization. More than 20 native taxa have become extinct in the past century (Minckley and Douglas, 1991). The plight of the razorback sucker (Xyrauchen texanus) typifies that of many western, "big-river" fishes (reviewed by Minckley et al., 1991). Historically, this large catostomid was widespread and abundant throughout the Colorado River basin, to which it is endemic. Various impacts of human intervention have combined to extirpate the species from most of its former range and reduce population sizes elsewhere. The largest rem<,tiiiing populations are in the upper Green River, Colorado-Utah (estimated by Lanigan and Tyus [ 1989] at fewer than 1000 adult individuals), and Lake Mohave, Arizona-Nevada (approximately 55,000 adults [Marsh, 1993]). Natural populations elsewhere, including the vast Gila River basin of Axizona, are either extirpated or too small to obtain reliable estimates of size (McAda and Wydoski, 1980; Minckley, 1983; Lanigan and Tyus, 1989; Marsh and Minckley, 1989). Despite more than a decade of active management, its status remained precarious, and the razorback sucker was federally listed as endangered (U. S. Fish and Wildlife Service [USFWS), 1991). Although razorback suckers continue to spawn and produce larvae in both large rivers and reservoirs (Marsh and Langhorst, 1988; Marsh and Papoulias, 1989; Marsh and Minckley, 1989; Marsh, 1993), all populations are otherwise comprised only of adults, thought to average 2~ to more than 40 years of age. Juveniles are virtually unknown and retzruitment to