7406

• UCREFRP Catalog Number: 7406
• Author: Bestgen, K. R.
• Title: Status Review of the Razorback Sucker,
• USFW Year: 1990.
• Copyright Material: NO

vary widely. In the northern portion of its range, razorback
suckers may overwinter in ice-covered riverine environments, and
in summer, water temperatures often exceed 25 C. In downstream
reaches of the mainstream Colorado River near Yuma, Arizona, where
razorback suckers were formerly abundant, winter water
temperatures were rarely below 10 C, but summer temperatures often
approached 32 C (Dill 1944). Bulkley and Pimentel (1983) reported
that optimal summer water temperatures for razorback suckers were
22-25 C, based on temperature preference and avoidance
experiments. Estimated upper temperature range avoidance (27.4-
31.6 C) depended upon acclimation temperature, but lower avoidance
temperatures (8.0-14.7 C) were independent of acclimation
temperature.
Little is known of the habitat associations of larval
razorback suckers in riverine habitats. Sigler and Miller (1963)
and Tyus (1987, identification tentative, pers. comm., D. E.
Snyder, Colorado State University) collected larval razorback
suckers in shallow, quiet shoreline areas in the lower Colorado
River, Arizona, and upper Green River, Utah, respectively.
Razorback sucker larvae in the lower Colorado River were
concentrated on the stream margin in water that was substantially
warmer (21.1-24.4 C vs. 15.5 C) than mainstream temperatures
(Sigler and Miller 1963). Presumably, these life stages also
inhabited backwaters and other off-channel habitats that offered
refuge from high water velocities.
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