Indications of continued Lake Mead razorback sucker recruitment and management progression

Authors: Brandon Albrecht, Paul Holden, Ronald B. Kegerries

Year: 2009 (xli)

Abstract

An ongoing razorback sucker (Xyrauchen texanus) research project on Lake Mead, Arizona and Nevada, has been funded by the Southern Nevada Water Authority and the U.S. Bureau of Reclamation for 13 years. This study continues to document the presence of actual, wild razorback sucker recruitment in the form of young, sexually immature individuals. Continued recruitment denotes that the Lake Mead razorback sucker population is an anomaly in terms of razorback sucker persistence throughout the Colorado River drainage, despite similar non-native fish composition and densities as other locations. Fin ray aging data and back-calculation techniques have indicated that recruitment of razorback sucker on Lake Mead has occurred nearly every year. Furthermore, data collected indicate that high lake elevations - those typically associated with maximum amounts of inundated terrestrial vegetation- appear to be responsible for pulses in recruitment. However, beginning with the 2007 spawning period, we captured large numbers of juvenile/subadult and adult razorback suckers that, based on back-calculation techniques, were spawned under low and declining lake elevations. In fact, the largest number of recruits observed to date coincides with 2005, a low-water year, which alone produced 29 recruits thus far. We believe that cover - both vegetative and in the form of turbidity - provides protection and food resources for larval and juvenile razorback sucker, thereby enabling them to avoid predation by nonnative sportfish present in the system. As monitoring efforts continue, we expect to capture individuals spawned during 2007, 2008, 2009, and beyond. Continued monitoring efforts on Lake Mead should help ascertain if recruitment events continue, and to help understand more fully how to enable this unique trend in other locations. This year a Lake Mead Razorback Sucker Work Group consisting of various state and federal agencies was formalized. In addition, a management plan was developed to present goals, tools, and infrastructure currently available for the conservation of Lake Mead razorback sucker. It is our hope that this management plan will facilitate adaptive management, help in further understanding this unique population, and benefit other researchers focused on razorback sucker recovery efforts.