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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />i <br />~. <br />I' <br />J" <br /> <br />~, <br />ft. <br />'''; <br /> <br />Ii <br /> <br />.~_.- <br /> <br />-.............. <br /> <br />16 <br /> <br />(Nessler et al. 1988). Large flow events only occur every few years, thus recruitment <br /> <br /> <br />would be expected to be variable from year to year (Walker et al. 1995), perhaps because <br /> <br /> <br />young require backwaters as nurseries. Recruitment mayor may not be due to availability <br /> <br /> <br />of backwaters, however, but simply a result of the large influx of nutrients and detrital <br /> <br /> <br />material associated with high flows and scouring and resetting of the channel habitat. <br /> <br /> <br />Native suckers (Catostomus spp.) often show good recruitment following scouring floods <br /> <br /> <br />of relatively short duration in small streams (W.L. Minckley , Arizona State University, <br /> <br /> <br />personal communication). Spawning of razor backs in the lower basin, however, occurs <br /> <br /> <br />prior to peak flows (typically in late April-July) in the Colorado River, although <br /> <br /> <br />coincident with peak flow in the smaller drainages, such as the Salt and Gila Rivers <br /> <br /> <br />(Rinne 1973). It is not understood why the apparent uncoupling of spawning with flows <br /> <br /> <br />in the lower river occurs, although with the more alluvial nature of habitat in the lower <br /> <br /> <br />river it may allow survival of young. Timing of spawning may further be an artifact of <br /> <br /> <br />the current reservoir environment which may lack or provide misleading environmental <br /> <br />cues. <br /> <br />Razorbacks exhibit protracted spawning across the entire spawning season, with <br /> <br /> <br />females releasing only a portion of their gametes with each event. Individual fish may <br /> <br /> <br />release up to 100,000 eggs over the course of the season, and appear to be able to spawn <br /> <br /> <br />over their entire life-span which approaches 50 years (Minckley 1983; McCarthy and <br /> <br /> <br />Minckley 1987). Females potentially produce several million eggs during their lifetimes. <br /> <br />High fecundity suggests low chances of survival for larvae and a life-history strategy for <br /> <br /> <br />an unpredictable environment. Larvae hatch in 5-10 days depending on water <br />