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

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razorback suckers in warmer, more productive wetlands may increase overall survival by
shortening the period of vulnerability to predation by small, gape-limited fishes (Lentsch et al.
1996a). Early juvenile razorback suckers were recently found during late summer or autumn
draining of the Old Charlie Wash managed wetland adjacent to the middle Green River (Modde
1996, 1997). Despite the predominance of nonnative fishes (including several known fish
predators), 28 razorback sucker juveniles (74-125 mm TL; mean, 94 mm TL) were collected
from the wetland in October 1995, and 45 (44-83 mm TL; mean, 66 mm TL) were collected in
August 1996. It is unknown whether these fish originated from riverine spawning and drifted
into Old Charlie Wash as larvae or were spawned in the wetland. Modde (1997) reported that
favorable nursery conditions for young fish existed in Old Charlie Wash during spring and
summer each year, 1995 and 1996; e.g., abundant zooplankton (peak mean density of organisms
was 54.3/1 in 1995 and 42,8/1 in 1996), warm water (about 16-280C; 2-80C higher than the
adjacent river), and abundant vegetative cover. Modde et al. (1996) associated years of high
spring discharge and floodplain inundation in the middle Green River (1983, 1984, and 1986)
with subsequent suspected recruitment of young adult razorback suckers.
Most floodplain wetlands adjacent to the Green River are now isolated from the main
channel by levees, and the historic frequency, magnitude, and duration of seasonal overbank .
flooding in the Green River have been substantially reduced since closure of Flaming Gorge Dam
in 1962 (Lentsch et al. 1996a; Modde 1997; USFWS 1997). Restoring access to these habitats
appears crucial for recovery of self-sustaining razorback sucker populations. The Colorado River
Recovery Implementation Program recently instituted efforts to reestablish river-wetland
connections at selected sites along the middle Green River by breeching levees (Lentsch et al.
1996a). However, substantial increases in the spatial extent of floodplain inundation and
duration of river-wetland connectivity will require management of spring-peak releases from
Flaming Gorge Dam in wet years when discharge from the Yampa River (and other tributaries) is
high to provide the magnitude and duration of flows necessary for overbank flooding (e.g., FLO
Engineering, Inc. 1996, 1997; Bell et al. 1998). Wick (1997) recommended that peak releases
from Flaming Gorge Dam be closely coordinated with forecasts of spring-runoff for the Yampa
River in order to support and build on Yampa River peak flows, Further, the seasonal timing of

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