9720

• UCREFRP Catalog Number: 9720
• Author: U.S. Fish and Wildlife Service.
• Title: Razorback sucker ‎(Xyrauchen texanus)‎ genetics management and captive propagation plan, Dexter National Fish Hatchery and Technology Center.
• USFW Year: 2004.
• USFW - Doc Type: Dexter National Fish Hatchery and Technology Center
• Copyright Material: NO

reservoirs linked by cold, clear, high velocity waters. The lower basin recovery unit exists as a
series of discrete reservoirs that present management opportunities markedly different than waters
in the upper basin. Razorback sucker management in the lower basin is dependant on
augmentation stocking in an attempt to enhance remaining RBS populations, and to conserve
extant genetic material of the largest remaining stock of RBS in the Colorado River system.
Recruitment failure is the most critical challenge in the lower basin reservoirs. Inundation
of nursery areas and predation by non-native fish on eggs, larvae, and early juvenile stages are
major causes of recruitment failure (Minckley et al. 1991). Without natural habitat, captive
rearing of early life history stages and advanced juveniles is required to maintain current
populations status. Wild caught and hatchery spawned RBS fry are reared in hatcheries and
ponds to a minimum length of 300 mm, PIT (passive integrated transponder) tagged, and stocked
to restore extirpated or augment remnant populations of RBS.
All lower basin reservoirs (Mead, Mohave, Havasu, and Imperial) have documented
historical populations of RBS (Minckley 1991). The resident RBS populations in Lake Havasu
and Imperial Reservoir are considered extirpated, and management efforts to reestablish a
population through augmentation in Lake Havasu began in the early 1990s. Since 1993, Lake
Havasu Fisheries Improvement Program, Bureau of Land Management, U. S. Fish and Wildlife
Service, and the Arizona Department of Game & Fish have cooperated to release over 30,000
subadult RBS into the reservoir. Visual observations by U. S. Fish and Wildlife Service sampling
crews indicate the fish are surviving and adult fish are utilizing numerous spawning sites
throughout the lake (C.O. Minckley, FWS, Pers comm. 2002).
The Lake Mead population, abundant in the 1960s, is estimated at less than 150 adults
inhabiting two distinct areas (Las Vegas Bay and Echo Bay) Holden et al. 1999; Abate et al.
2002). The Nevada Division of Wildlife released 26 subadult RBS fish into Las Vegas Bay in
1994, and 14 into Echo Bay in 1995. All the fish were PIT tagged and had originated from the
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