7954 - Laserfiche WebLink

Home Browse Search

American Fisheries Society Symposium 15:102-111, 1995 An Augmentation Plan for Razorback Sucker in the Upper Colorado River Basin TIMOTHY MODDE U.S. Fish and Wildlife Service, Colorado River Fish Project 266 West 100 North, Suite 2, Vema? Utah 84078, USA ALLAN T. ScxoLz Eastern Washington University, Department of Biology Cheney, Washington 99004, USA J. HOLT WILLIAMSON U.S. Fish and Wildlife Service, Dexter National Fish Hatchery and Technology Center Post Office Box 219, Dexter, New Mexico 88230, USA G. BRUCE HmNES U.S. Fish and Wildlife Service, Colorado River Fish Project 266 West 100 North, Suite 2, Vemal Utah 84078, USA BOB D. BURDICK AND FRANK K. PFEIFER U.S. Fish and Wildlife Service, Colorado River Fish Project 764 Horizon Drive, South Annex A, Grand Junction, Colorado 81506, USA Abstract.-The Endangered razorback sucker Xyrauchen texanus historically occupied the major tributaries of the Colorado River system. Habitat loss due to water development, predation and competition from nonnative fish, and contaminants have resulted in decreases in population size such that razorback suckers in the upper Colorado River basin are consistently collected in only the middle Green River. An augmentation plan is proposed that integrates habitat improvement (viz, flooded bottomland enhancement) with reintroduction. The goal of an augmentation program for razorback sucker is the establishment of viable (i.e., persistent), locally adapted populations. The basic genetic conservation unit was defined as the local spawning population and was delineated by river tributaries. A decision-making process, based on the threats of inbreeding depression and genetic drift, to determine whether a rare population should be augmented is presented. Populations that have sufficient size to prevent the probability of inbreeding (N > 250) and to reproduce successfully should not be augmented. Rather, resources should be directed toward habitat restoration. Genetic manage- ment incorporates the establishment of a refugium stock represented by the offspring of a spawning matrix of a minimum of five wild males and five wild females. In addition to providing refugia to the genetic diversity in wild populations, these fish may serve as broodstock for future reintroduction efforts. If reintroduction is necessary, synthetic imprinting will be incorporated to influence behavior and distribution of stocked fish following stocking. The razorback sucker Xyrauchen texanus is a rel- atively large, monotypic catostomid endemic to the larger tributaries of the Colorado River drainage. Once abundant, this fish has been extirpated from most of its historical range and is now found con- sistently in only the middle Green River and Lake Mohave (Minckley et al. 1991). The widespread decline of this fish and the continuation of threats to its viability have resulted in listing it as an Endan- gered Species (USFWS 1991). The major factor associated with the decline of the razorback sucker is the interruption of natural water flow patterns via water diversions and upstream impoundments that alter both the timing and quantity of historical flows (Tyus and Karp 1989, 1990; Minckley et al. 1991). 1615'` These alterations have decreased historic habitat and created main-channel barriers that block migra- tion to historical spawning sites (Minckley 1983). Additionally, predation and competition from non- native fishes (Behnke and Benson 1980; Marsh and Brooks 1989) and toxic heavy metal contamination (Stevens et al. 1992; Ono et al. 1983) have contrib- uted to the decline of razorback sucker. The factors described above have impaired the ability of the razorback sucker to recruit throughout its range (McAda and Wydoski 1980; Tyus 1992). The remaining populations are composed of older nonrecruiting adults (Lanigan and Tyus 1989; Marsh and Minckley 1989), with most individuals 30 to 40 years old (McCarthy and Minckley 1987). In 102