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

populations in razorback sucker critical habitat (Hawkins and Nesler 1991; Maddux et al. 1993;
Lentsch et al. 1996b; Tyus and Saunders 1996; USFWS 1997; Hamilton 1998).
Remaining wild populations of razorback sucker are in serious jeopardy, The largest
extant concentration is a remnant population found above Davis Dam in Lake Mohave on the
lower main-stem Colorado River, Arizona-Nevada, but no natural recruitment to the population
has occurred in recent decades and estimated numbers of adults declined 68% (from 73,500 to
23,300) during 1980-1993 (Marsh 1994). Most riverine razorback suckers are now limited to the
upper Colorado River basin and populations are small. The largest riverine population exists in
flat-water reaches of the middle Green River, northeastern Utah and northwestern Colorado,
between and including the mouths of the Yampa and Duchesne rivers (Tyus 1987). Lanigan and
Tyus (1989) used a demographically closed model with capture-recapture data collected from
1980 to 1988 and estimated that the middle Green River population consisted of about 1,000
adults (mean, 948; 95% confidence interval, 758-1,138). Based on a demographically open
model and capture-recapture data collected from 1980 to 1992, Modde et al. (1996) estimated the
number of adults in the middle Green River population at about 500 fish (mean, 524; 95%
confidence interval, 351-696). Modde et al. (1996) characterized the population as
"precariously" small but dynamic, with at least some recruitment.
Captures of ripe fish and tracking movements of adults in spring were used to locate
razorback sucker spawning areas in the middle Green River. McAda and Wydoski (1980) found
a presumptive spawning aggregation of 14 ripe razorback suckers over a cobble bar (stones
20-50 cm in diameter) at the mouth of the Yampa River during a 2-week period in early and
mid-May 1975. Those fish were collected from water about 1 m deep with a velocity of about 1
m/s and temperatures ranging from 7 to 160C (mean, 120C). Three spawning reaches were
reported by Tyus (1987): (1) Island and Echo parks of the Green River in Dinosaur National
Monument, including the lower kilometer of the Yampa River; (2) the Jensen area of the Green
River from Ashley Creek to Split Mountain Canyon; and (3) the Ouray area of the Green River,
including the lower few kilometers of the Duchesne River. The Jensen area contributed 73% of
the 60 ripe razorback suckers caught over gravel and coarse sand substrates in those three reaches
during spring 1981, 1984, and 1986; water temperatures at capture locations ranged from 10 to

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