8142

• UCREFRP Catalog Number: 8142
• Author: Horn, M. J.
• Title: Nutritional Limitation of Recruitment in the Razorback Sucker ‎(
• USFW Year: 1996.
• Copyright Material: NO

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largest numbers occurring in reservoirs, from where they moved or were carried to lotic

habitats. Unlike canyon-bound reaches or narrow, bedrock-constrained channels of

smaller low desert streams exposed to violent flooding which reduced nonnative

populations, flooding in the low-gradient, lower Colorado River may have had little affect

on non-native species (see Minckley and Meffe 1987). Minckley (1991) considered

predatory, competitive, and other biotic pressures of non-native on native fishes the most

important factors now forcing native biotas of western North America toward extinction

(see also, contributions in Minckley and Deacon 1991).

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3. Study Organism, the Razorback Sucker
I studied the razorback sucker, a large-bodied, long-lived,

iteroparous species endemic to the Colorado River system of western North America

(Minckley 1973, 1983), as a species adapted to conditions in a large, highly seasonal

river. To successfully recruit in the natural state, I assume this species depends on cues

and conditions provided by fluctuating seasonal discharge, as with other large fishes in
large-river habitat (Lowe-McConnell 1987; Junk et al. 1989; Winemiller 1989; Schlosser
1991; Gherke 1992).

Closely spaced gill-rakers and a sub-terminal mouth suggest adaptations for

feeding in a benthic environment (Hubbs and Miller 1953; Minckley et al. 1991). In

reservoirs adult diets consist largely of filtered zooplankton which they collect in mid-

water (Roden 1978; Marsh 1987). In the river, mainstem, eddy or backwater habitats,

diet consists mainly of benthic material composed of chironomids and detritus.