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production in water temperatures that average 14 ° C. Studies by Inslee (1982) and Hamman (1985) indicated that optimum temperatures for reproduction were 20-22°C. Marsh (1985) experimentally controlled temperature to determine effects on hatching success of razorback sucker eggs: of six temperatures, 20°C resulted in highest hatching success, followed by 25'C. There was a significantly lower hatching success at 15'C, and complete egg mortality at 5, 10, and 30°C. Haines (1995) performed similar experiments at temperatures of 12, 16 and 20 ° C, and found that hatching success increased with increasing temperatures and ranged from 48% (12 ° C) to 67% (20'C). The availability of water temperatures near 20°C immediately following spawning is therefore an important variable influencing the reproductive success of this species. Main channel temperatures in the Colorado River during spring runoff, when razorback suckers are generally found in spawning condition, are well below the optimum for egg incubation and hatching success (20°C) averaging 13 °C at Cameo (USGS gauge). Osmundson and Kaeding (1991) suggested that razorback suckers in the upper Colorado River may spawn in warm, flooded, off-channel habitats as a means to sidestep the cool waters of the main channel thereby allowing them to extend the limits of their range far upstream. Timing reproduction to coincide with spring runoff allows access to these flooded off-channel habitats. One benefit of off-channel spawning is the assurance that all larvae produced will be placed directly within, productive, rearing habitats (see below). Alternatively, mid-channel spawning of razorback suckers observed in the Green River system is believed to coincide with runoff to ensure that emerging larvae will have access to productive, flooded, off-channel habitats as they drift downstream (Tyus and Karp 1990, Muth et al. 1998). Survival of young razorback suckers has been documented in two off-channel habitats in recent years: Old Charley Wash, beside the Green River in Utah, and Etter Pond, beside the Colorado River near De Beque, Colorado. Modde (1996) found 28 young-op- the-year (YOY) razorback suckers in Old Charley Wash in 1995 and Elmblad (CDOW, personal communication) captured 165 adults from Etter Pond. A Lincoln-Peterson mark- recapture effort provided an estimate of 575 adults in the pond (95% CI = 320-830). Genetic analyses of the Etter Pond fish indicated that almost all were siblings and otilith 10