9560

• UCREFRP Catalog Number: 9560
• Author: Valdez, R. A.
• Title: A Generalized Interactive Model to Predict Floodplain Habitat Area Needed to Recover the Endangered Razorback Sucker in the Upper Colorado River Basin - Floodplain Model Version 5.1.
• USFW Year: 2004.
• USFW - Doc Type: Logan, UT.
• Copyright Material: NO

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(Hamman 1985, 1987), and under varying laboratory conditions (Papoulias 1988). Hamman
(1985) reported 61 % hatching success at 20-220C, and Marsh (1985) reported 19% success at
150C. Studies by Bozek et al. (1984) on razorback sucker in Lake Mohave revealed hatching
success of 22-57% at lOoC; 32--65% at 150C; 34-65% at 20oC; and 0% at 80C.
Data on larval survival are currently limited to observations in ponds at hatchery
facilities. Hamman (1985) reported 88-98% survival in outdoor ponds under variable spring
temperatures, and Hamman (1987) reported 93-96% survival at 20-220C under controlled
conditions. Hatching success and survival of larvae are highly variable in the literature and data
are not available for riverine spawning bars. Hence, these two variables are provided as user--
specified input variables in the model.
3.6 Larval Drift

There are currently no quantitative estimates of larval razorback sucker drifting
downstream from spawning bars. Estimates of drifting tlannelmouth sucker (Catostomus
latipinnis) from the Upper Colorado River near Parachute, Colorado, provide some insight into
likely drift patterns and densities of razorback sucker. Sampling of drift over a 9-week period
revealed that 71 % of the fish drifted during a 3'-week period, from July 25 to August 15, 1983,
when water temperatures were 16-200C (Valdez et al. 1985). Maximum weekly drift densities
of 1.91 fishl1,000 cubic feet of water (efw) occurred at 9,750 cfs; 1.65 fish/l,OOO cfw at 8,230
cfs; and 1.21 fish/1,000 cfw at 7,375 cfs. Approximately 36.8% of the drift was composed of
tlannelmouth sucker, and it is estimated that daily drift during these 3 weeks was 592,106;
431,763; and 283,732 tlannelmouth sucker larvae. Weekly drift is estimated at 4,144,742;
3,022,341; 1,986,124 larvae for a total of9,153,207Iarvae during the 3-week period. Assuming
that this period accounted for 71 % of the total number of drifting larvae, it is estimated that in
1983, a total of 12,891,841 tlannelmouth sucker larvae drifted past the Parachute sampling site.
These estimates provide some order of magnitude of the potential production by riverine
catostomids, such as tlannelmouth sucker and razorback sucker.
3.7 Larval Entrainment in Floodplains
There are also no quantitative'estimates of entrainment of drifting larvae in tloodplains.
Studies of drifting tlannelmouth sucker and bluehead sucker (Catostomus discobolus) near

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