7984

• UCREFRP Catalog Number: 7984
• Author: Maddux, H. R., L. A. Fitzpatrick and W. R. Noonan.
• Title: Colorado River Endangered Fishes Critical Habitat - Draft, Biological Support Document.
• USFW Year: 1993.
• USFW - Doc Type: Salt Lake City, Utah.
• Copyright Material: NO

Recent research in Davis and Yuma coves on Lake Mohave sponsored by the Bureau of
Reclamation (Reclamation) has shown that razorback sucker larvae can survive and grow
successfully if the predator load is reduced (Burke 1992).
HABITAT REQUIREMENTS
Although habitat use of razorback suckers has been studied for years, the habitat preferences
and factors limiting their abundance in native riverine habitats are not well known because of
the scarcity of extant populations (Minckley 1983; Lanigan and Tyus 1989) and the absence
of younger life history stages (Minckley et al. 1991). However, based on available data
taken from the Green River, Tyus and Karp (1989) considered the lack of low winter flows,
high spring flows, seasonal changes in river temperatures, and inundated shorelines and
bottomlands as factors that potentially limit the survival, successful reproduction, and
recruitment of this species.
Spawning Habitat
Reproduction and habitat use of razorback suckers has been studied in lower basin reservoirs,
especially in Lake Mohave. Fish reproduction has been visually observed near reservoir
shorelines for many years, and spawning in the reservoir usually lasts from January or
February to April or May. The fish spawn over mixed substrates that range from silt to
cobble, and at water temperatures ranging from 51 ° to 70°F (reviewed by Minckley et al.
1991).
Habitat use and spawning behavior of 307 adult razorback suckers in riverine habitats were
studied by fish captures and radiotelemetry in the Green River Basin (Tyus and Karp 1990).
The fish there spawned in the spring with rising water levels and increasing temperatures.
The fish moved into flooded areas in early spring, and they made spawning migrations to
specific locations as they became reproductively active. Spawning occurred over rocky runs
and gravel bars. It has been observed that several males accompany a single female (Jonez
and Sumner 1954; Ulmer 1980).
In the Upper Basin, spawning occurs from April through June 14 (Tyus 1987; Osmundson
and Kaeding 1989; Tyus and Karp 1990). Water temperatures recorded in the upper Green
River during spawning ranged from 48° to 63°F (Tyus and Karp 1990). McAda and
Wydoski (1980) reported spawning fish in May over cobble substrates, about 3.2 feet/sec.
water velocity and 3.2 feet water depth. Tyus (1987) collected ripe adults over coarse sand
substrates and in the vicinity of gravel or cobble bars, but direct observation of spawning
was not possible because of high turbidities prevalent during that time of year. Osmundson
and Kaeding (1989) suggested that flooded bottomlands in the Grand Valley were historically
the primary spawning habitats. McAda and Wydoski (1980) collected running ripe females
from a gravel pit where they were probably spawning. Tyus and Karp (1990) found the
average water depth of the gravel and cobble bars to be 2 feet with an average water velocity
of 2.4 feeds.
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