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

overbank flooding must be matched with the temporal distribution of razorback sucker larvae in
the river (Modde 1997). We estimated that, in most years during 1993-1996, larval razorback
suckers in the Green River were first captured 20-30 d after initiation of spawning, which
generally coincided with a relatively steep and consistent increase in discharge associated with
the beginning of spring runoff, and numbers collected had usually peaked by early or mid-June,
The present existence of razorback sucker populations in the Green River is tenuous, and
immediate conservation measures are needed if the species is to persist. Management actions of
the Colorado River Recovery Implementation Program to recover the endangered fishes include a
combination of restoration of natural habitats, nonnative fish control, augmentation of wild
populations, protection offish in refugia, and monitoring of populations and habitats. We
documented annual reproduction by razorback suckers but mortality of larvae was apparently
high. Predation on razorback sucker early life stages by nonnative fishes is considered a serious
threat to populations (Bestgen 1990; Minckley et al. 1991; USFWS 1997), and concerns exist
within the Colorado River Recovery Implementation Program about the effects of degraded
water quality (e.g" increased concentrations of selenium) on razorback sucker reproduction and
larval survival (Hamilton and Waddell 1994; Hamilton 1998; Hamilton et al. 1998). Restoring
access to warm, productive floodplain wetlands to serve as growth and conditioning habitats
holds promise for razorback sucker recovery, but much remains to be learned about fish
population and community responses to individual and collective management actions.

RECOMMENDATIONS

1. Development of an effective standardized monitoring program for razorback suckers in
the Green River is progressing and requires continued flexibility in application and
evaluation of sampling methods, data analysis, and overall scope of the program to ensure
that population indices are valid indicators of trends and responses to management
actions.
2. Light traps set overnight in quiet-water habitats are effective for capturing larval
razorback suckers to document reproduction and monitor when larvae are transported
downstream from spawning areas. However, studies are needed to directly assess the

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