8022

• UCREFRP Catalog Number: 8022
• Author: Muth, R. T., et al.
• Title: Reproduction and Early Life History of Razorback Sucker in the Green River, Utah and Colorado, 1992-1996.
• USFW Year: 1998.
• USFW - Doc Type: 34,
• Copyright Material: NO

of nonnative adult red shiners on the mortality of larval Colorado squawfish decreased 5-40% as
growth rates of larvae increased by O,l-mm increments from 0.2 to 0.6 mm TL/d. Predation by
adult red shiners on larvae of native catostomids in flooded and backwater habitats of the Yampa,
Green, or Colorado rivers was documented by Ruppert et al. (1993) and Muth and Wick (1997).
Horn (1996) concluded that although nutritional limitations in Lake Mohave may directly
contribute to the high mortality of larval razorback suckers, a greater problem is reduced growth,
which keeps larvae at a size vulnerable to predation for longer period of time. He further stated
that apparently all razorback sucker larvae in Lake Mohave, starving or not, are consumed by
nonnative fish predators.

Management Implications

Most collections of wild adult razorback suckers in rivers of the upper Colorado River
basin have occurred in unconfined floodplain reaches (Modde et al. 1995; Muth 1995), and the
greatest expanse of floodplain habitat in the upper basin is in the Jensen and Ouray reaches of the
middle Green River (Irving and Burdick 1995), coincident with the largest extant reproducing
population. Floodplain wetlands inundated and connected to the main channel by spring-runoff
discharges appear to be important habitats for all life stages of razorback sucker (e.g.,
Osmundson and Kaeding 1989; Tyus and Karp 1989, 1990, 1991; Modde 1996, 1997; Modde et
al. 1996). Floodplain wetlands are typically warmer and more productive than the adjacent river,
have abundant vegetative cover, and the natural integrity of large-river ecosystems is dependent
on interactions between the main channel and floodplain (Welcomme 1985; Junk et al. 1989;
Ward 1989; Stanford 1994; Ward and Stanford 1995; Brookes 1996; Wetzel and Ward 1996;
Wydoski and Wick 1998).
The seasonal timing of razorback sucker reproduction suggests an adaptation for utilizing
floodplain wetlands. Tyus and Karp (1990) and Modde and Wick (1997) reported that adult
razorback suckers in the middle Green River moved into flooded habitats (e.g., wetlands and
tributary mouths) shortly before or after spawning. They suggested that this movement was
related to temperature preferences and food abundance. Razorback sucker larvae drift
downstream after swimup and are transported into nursery habitats. Enhanced growth of larval

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