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17 <br />DISCUSSION <br />Although more than two thousand razorback suckers have been taken in <br />Lake Mohave in the past decade, none (exclusive of larvae) has been <br />smaller than ca. 400 mm TL (Bozek et al. 1984, Minckley 1983, unpubl. <br />data). McCarthy (1986) showed that even the smallest individuals among <br />these specimens were are greater than 20 years of age. Frequency <br />distributions based on available lengths are unimodal for both sexes <br />(separated because of known dimorphism [Hinckley 1983]). There is no <br />evidence of recruitment to the adult population. The last juveniles <br />taken in the Lake Mohave area were collected in 1950 when 6,100 <br />specimens (12-42 mm) were seined near Cottonwood Landing (present site <br />of Cottonwood Cove [Fig. 1]) just before Lake Mohave filled (Minckley <br />1983). <br />We know of no recent reports of razorback sucker spawning aggre- <br />gations in the lower Colorado River other than in Lake Mohave and <br />Senator Wash Reservoir, California. The last habitat, an off-stream <br />pump-storage reservoir, supports a small (ca. 50 adults), remnant <br />population which, like that in Lake Mohave, shows no evidence of <br />recruitment (Ulmer 1985). Yet, since the mid-1970s at least a dozen <br />razorback sucker smaller than ca. 400 mm TL have been collected in <br />canals fed by the Colorado River downstream from Davis Dam (Ulmer 1985, <br />unpubl. data). We propose an hypothesis in attempt to explain this <br />phenomonon, and to help elucidate fate of larval razorback sucker in <br />Lake Mohave. <br />Adult razorback sucker appear to reproduce prolifically in Lake <br />Hohave, especially in the Arizona Bay area. Larval suckers become <br />available annually from February through April, attain average lengths