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<br />(1992) estimated at approximately 60,000. Minckley et al. (1991) report that limited numbers <br />of razorback suckers have been found in Lake Havasu, the Central Arizona Project aqueduct <br />(near the Lake Havasu intake), and from the Colorado River downstream of Parker Dam in <br />irrigation ditches and in Senator Wash Reservoir but that an approximate 10-year reintroduction <br />program in central Arizona rivers has had little success. <br /> <br />Minckley (1983) reported that 18 razorback suckers were recorded by investigators at various <br />localities in Lake Mead from 1967 to 1980, and in 1990 Jon Sjoberg (Nevada Department of <br />Wildlife, personal communication) reported sighting and capturing small numbers of razorback <br />suckers in western Lake Mead. Using helicopters to locate aggregations, 36 razorback suckers <br />in western Lake Mead were captured and tagged in 1992 (Heinrich and Sjoberg 1992, Burke <br />1992). No razorback suckers were reported from a 1991 survey of selected locations in eastern <br />Lake Mead (Baucom 1991). <br /> <br />In the Grand Canyon area, razorback suckers rarely have been collected. Carothers and <br />Minckley (1981) collected one and observed three in or near the Paria River (1978-1979). A <br />razorback sucker was collected in and released near Rm 108 in the mainstem (1984) and, at the <br />mouth of the LCR, one was captured in 1989 and five were PIT tagged in 1990 (Dennis Kubly, <br />Arizona Game and Fish Department, personnel communication). <br /> <br />Adults <br /> <br />Because adult razorback suckers are the second largest native fish in the Colorado basin, average <br />total length in Lake Mohave was 550 mm for males and 620 mm for females (Marsh and <br />Minckley 1992), it has been feasible to implant them with radio or ultrasonic transmitters to <br />track movements and habitats utilized. Marsh and Minckley (1991) found radio-tagged <br />individuals transplanted to the Gila River above San Carlos Reservoir, Arizona' to use mid- <br />channel habitats that were wide runs with sand substrate. Quieter habitats such as backwaters, <br />eddies, and deep pools were selected by few fish. Radio-tagged razorback suckers (Tyus 1987) <br />used the mid-channel sand bars of the flat-water reaches of the upper Green River and lower <br />Duchesne River in summer rather than deep pools. Velocities of these habitats were slow (05 <br />mts) and depths were about 1.5 m. Of the over 300 razorback suckers captured in his study, <br />none used the white-water canyon reaches. <br /> <br />In contrast are the recollections of first-hand observers from the early 1900's, reported by <br />Minckley (1973) and Minckley et al, (1991), that razorback suckers were in eddies, backwaters, <br />or deep holes and were sometimes fished by snagging. Holden and Stalnaker (1975) in a basin <br />wide study from the upper Yampa and Green Rivers down to Glen, Marble, and Grand Canyons <br />on the Colorado River found razorback suckers only in "stagnant or quiet-water areas," They <br />identified one concentration site as wash confluences during high water of early summer in <br />Canyonlands National Park. Bestgen (1990) remarked on the greater, perhaps even year-round, <br />use of lentic and backwater habitats by razorback suckers compared to the other "big river" <br />fishes. Further evidence of this may be the success in raising and maintaining razorback suckers <br />in ponds and lakes that has been observed by many who work with the species. <br /> <br />13 October 1993 Draft biological opinion 2-21-93-P,167 <br /> <br />13 <br />