Razorback sucker studies on Lake Mead, Nevada: 1998-1999 annual report

Holden, Paul; Abate, Paul; Ruppert, Jack

This is a report on the studies done on the razorback sucker (Xyrauchen texanus) in Lake Mead from 1998-1999, including study areas, spawning areas, fish distribution numbers, and tagged fish locations.... 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 eta!. 1991). The distribution and abundance of the razorback sucker is greatly reduced from historic levels, and it is one of four large-river fishes endemic to the basin that is presently considered endangered by the U.S. Department of the Interior (USFWS 1991). One of the major factors causing the decline of the razorback sucker and the 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 eta!. 1977, Wicket a!. 1982, Minckley et a!. 1991). Competition and predation from nonnative fishes which have successfully established in the river have also contributed to their decline. Razorback suckers have persisted in many of the reservoirs that were constructed in the lower Colorado River Basin, with the largest population occurring in Lake Mohave, Arizona and Nevada (Minckley eta!. 1991). However, these populations are comprised primarily of adult fish with little natural recruitment. Adult razorback sucker are most evident in these reservoirs from January through April when they congregate in shallow shoreline areas to spawn, and larvae can be very numerous soon after hatching. Predation by bass, carp, catfish, sunfish, and other nonnative species appears to be the major reason for the lack of razorback sucker recruitment (Minckley eta!. 1991).

Razorback sucker studies on Lake Mead, Nevada: 1998-1999 annual report

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