9523

• UCREFRP Catalog Number: 9523
• Author: Birchel, G. J. and K. Christopherson.
• Title: Survival, Growth and Recruitment of larval and Juvenile Razorback Suckers ‎(Xyrauchen texanus)‎ Introduced into Floodplain Depressions of the Green River, Utah.
• USFW Year: 2004.
• USFW - Doc Type: Vernal.
• Copyright Material: NO

INTRODUCTION
~ Since the construction of Flaming Gorge Dam, the magnitude and duration of
spring peak flows in the Green River have decreased (Muth et al. 2000). This has

reduced the frequency and duration of the river-floodplain connection. Floodplains are
presumed to be important rearing habitat for the endangered razorback sucker
(Xyrauchen texanus) (Wydoski and Wick 1998; Muth et al. 1998; Lentsch et al. 1996a).
~ Elevated temperatures, nutrients and light intensities combine to make floodplain
wetlands areas of high primary productivity (Birchell et al. 2002; Wydoski and Wick
1998; Lentsch et al. 1996a; Cooper and Severn 1994), and zooplankton density (fish
~ food items) is also high.
Wydoski and Wick (1998) summarized data collected from zooplankton studies
conducted in the Upper Colorado River Basin. Zooplankton densities (mean number of
organisms/liter) were lowest in the main channel (0 - 1.3), higher in backwaters (0 -
13.1) and highest in floodplain habitats (4.2 - 81.5). The minimum quantity of food
~ required by razorback sucker larvae to survive following swim-up is 30 - 60 shrimp
nipple per fish per day (Peepuls and Mickey 1992 in Wydoski and Wick 1998). The
highest density of zooplankton commonly occurs in floodplains along the middle Green
River, rarely in backwaters, and never in the main channel (Birchell et al. 2002;
Wydoski and Wick 1998). Reproduction by razorback sucker occurs in the spring
~ during peak flows when highly productive floodplain habitats are accessible to fish
(Muth et al. 1998). This seasonal timing of razorback sucker spawning, and drift,

indicates possible adaptation for using floodplain habitats (Muth et al. 1998).
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