Razorback sucker studies on Lake Mead, Nevada and Arizona: 2008-2009 final annual report

Keggerries, Ron; Albrecht, Brandon; Holden, Paul

This Annual Report presents the results of the 13th study year (February 2009 through early May 2009 monitoring data) and sonic-tagged razorback sucker data from July 2008 through June 2009, in accordance with the results reported by Albrecht et al. (2008a) and other past annual reports. Other information and data from previous years and reports are included as applicable.... INTRODUCTION The razorback sucker (Xyrauchen texanus [Abbott]) is an endemic fish species of the Colorado River Basin. It was historically widespread and common throughout the larger rivers of the Colorado River Basin (Minckley et al. 1991). The distribution and abundance of the razorback sucker are greatly reduced from historic levels, and it is one of four endemic, large-river fish species (i.e., Colorado pikeminnow [Ptychocheilus lucius], bonytail [Gila elegans], humpback chub [Gila cypha]) presently considered endangered by the U.S. Department of the Interior (USFWS 1991). One of the major factors causing the decline of razorback sucker and other large-river fishes has been the construction of mainstem dams and the resultant cool tailwaters and reservoir habitats that replaced a warm, riverine environment (Holden and Stalnaker 1975, Joseph et al. 1977, Wick et al. 1982, Minckley et al. 1991). Competition and predation from nonnative fishes that are successfully established in the Colorado River and its reservoirs have also contributed to the decline of these endemic species (Minckley et al. 1991). Razorback sucker persisted in several of the reservoirs that were constructed in the lower Colorado River Basin; however, these populations were comprised primarily of adult fish that apparently recruited during the first few years of reservoir formation. The population of long-lived adults then disappeared 40–50 years following reservoir creation and the initial recruitment period (Minckley 1983). The largest reservoir population, estimated at 75,000 in the 1980s, occurred in Lake Mohave, Arizona and Nevada, but it had declined to less than 3,000 by 2001 (Marsh et al. 2003). Mueller (2005, 2006) reports the wild Lake Mohave razorback sucker population to be approaching 500 individuals, while the most recent 2009 estimate of Lake Mohave razorback sucker determined there are approximately 30 wild fish remaining (Pacey 2009). Adult razorback sucker are most evident in Lake Mohave from January through April when they congregate in shallow shoreline areas to spawn, and larvae can be numerous soon after hatching. Today, the Lake Mohave population is largely supported by periodic stocking of captive-reared fish (Marsh et al. 2003, Marsh et al. 2005). Predation by bass (Micropterus spp.), common carp (Cyprinus carpio), channel catfish (Ictalurus punctatus), sunfish (Lepomis spp.), and other nonnative species appears to be the primary reason for lack of razorback sucker recruitment (e.g., Minckley et al. 1991, Marsh et al. 2003, Carpenter and Mueller 2008, Schooley et al. 2008).

Razorback sucker studies on Lake Mead, Nevada and Arizona: 2008-2009 final annual report

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