WSP02186

• File Number: 8220.101.09
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 11/1/1995
• Author: USDOI-BOR
• Title: Biological Assesment of a One Time Test of Beach/Habitat-Building Flow from Glen Canyon Dam-Spring 1996
• Water Supply Pro - Doc Type: Biological Opinion

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RAZORBACK SUCKER SPECIES ACCOUNT

Distribution and Abundance

Razorback sucker (RBS; Catostomidae: Xvrauchen t:exanus) is a widely
distributed, endemic, warm water Colorado River fish. RaS formerly occurred
throughout the Colorado River, but has declined since ~930 with the regulation
of the Colorado River (Dill ~944, Minckley ~991). The decline of RaS has been
attributed to thermal regime changes, altered spawning habitat and
introduction of non-native fish species, which have cumulatively resulted in
wide-scale recruitment failure (Bestgen 1990, Minckley 1991). This species
was listed as an endangered species by the U.S. Fish and Wildlife Service in
~991 (U.S. Fish and Wildlife Service 1991).

The largest RBS population in the Lower Colorado River Basin exists in Lake
Mohave, where it was estimated to be approximately 60,000 fish in 1989 (Marsh
and Minckley 1989). Other, smaller lower basin RaS populations occur in Lake
Mead, downstream from Hoover Dam, and in Senator Wash Reservoir. In the Upper
Colorado River Basin, RaS occur regularly in the upper Green and lower Yampa
rivers, and individual RaS have been collected at rare intervals in the
Colorado River near Grand Junction, Colorado, and in the major tributary arms
of Lake Powell. RaS are long-lived (20 to 50 yr), but most wild-caught RaS
are old individuals, and recruitment failure may lead to the rapid demise of
this species (McCarthy and Minckley ~987, Minckley ~991). Experimental
releases in the Upper Basin, and attempts to propagate RaS in Lower Basin
reservoirs are encouraging, but the mainstream Colorado River populations
continue to decline.

RBS are extremely rare in Grand Canyon. Recent observations are those of
Carothers and Minckley (~981) who reported four RaS from the paria River in
1978-1979; Maddux et al. (1988) reported one blind female RaS at Upper Bass
(Colorado River Mile 107.5) in 1984; and Minckley (1991) reported records of 5
additional RaS captured in the lower Little Colorado River from 1989-~990.
Putative hybrids between flannelmouth sucker (Catostomus 1at:;ninnis) and RaS
have been reported from the Little Colorado River (Suttkus and Clemmer 1979,
Carothers and Minckley 1981) .

Life Requisites

RaS are generally associated with calm river reaches, particularly man-made
lakes (Tyus 1987); however, river spawning typically occurs in riffle habitats
over gravel and cobble substrata (Mueller 1989). Larval RaS drift downstream
from the spawning habitat, and concentrate in warm, low-velocity areas (e.g.
flooded bottoms). These areas also support post-larval RaS, and channel and
mid-stream river habitats floored by fine-grained alluvium are important to
subsequent RaS life stages (MinCkley 1983, Tyus and Karp 1989, Minckley 1991) .
Springtime concentrations of adult RaS have been noted in side-channels, off-
channel impoundments, and in tributaries (Bestgen 1990, Minckley 1991) .
The optimal thermal range for RaS is 72 to 770F (Bulkley and Pimentel 1983) ;
however, RaS occur in widely varying temperatures. RBS habitats in the Upper
Colorado River Basin are ice-covered during winter, while the temperatures of

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