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148 <br />The Southwestern Naturalist <br />UTAH <br />Lake Powell <br />0 <br />C3 <br />;4PI#UTE <br />FARMS' <br />BLUFF <br />COLORADO <br />vol. 36, no. 1 <br />N <br />I <br />f <br />I <br />too - * 200 1 Navajo Reservoir 7 - - - - t- -7 -A!r <br />SHIPROCK <br />13 <br />0 <br />50 kilometers 300 FARMINGTON <br />I <br />STUDY AREA <br />A <br />ARIZONA NEW MEXICO <br />FIG. 1-Captures of Colorado squawfish and razorback sucker in the San Juan River, 1987 to 1989. Numerals <br />denote river kilometers. Dots indicate capture locations of adult and sub-adult Colorado squawfish, and stippling <br />indicates regions of capture of young-of-year Colorado squawfish. Solid arrows indicate capture sites of razorback <br />suckers, and hollow squares represent cities. <br />and Utah. The study area was the mainstream <br />San Juan River from Farmington, New Mexico, <br />downstream to Lake Powell, Utah, a reach of <br />approximately 320 river km. A total of 37 sam- <br />pling trips was conducted. Raft electrofishing of <br />main channel habitats occurred in spring, sum- <br />mer, and autumn and backwaters were seined in <br />late-summer and fall. Trammel nets, the main <br />gear used at the inflow area to Lake Powell col- <br />lections, were used on a limited basis in riverine <br />collections. <br />Ten adult Colorado squawfish were collected <br />or observed during this period. The eight adult <br />specimens collected ranged in size from 539 to <br />780 mm total length (TL), weighed from 1.1 to <br />5.5 kg, and were distributed from 4.4 km down- <br />stream of Shiprock, New Mexico, to Lake Powell, <br />Utah (Fig. 1). An individual captured in the San <br />Juan River arm of Lake Powell on 7 April 1987 <br />(615 mm TL) was subsequently recaptured on 8 <br />September 1987 (632 mm TL) during a night- <br />time electrofishing operation approximately 145 <br />river km upstream from the initial point of cap- <br />ture. During our study adult Colorado squawfish <br />were captured or sighted in the San Juan River <br />at least once in each month from April to October, <br />except July. <br />A total of 18 young-of-year (YOY) Colorado <br />squawfish, ranging in size from 17.2 to 39 mm <br />TL, was collected in low velocity habitats in the <br /> <br />March 1991 <br />San Juan River during 198 <br />were collected in the San Jua <br />near Lake Powell (river kilorr <br />one at RK 38.0, six close t( <br />Montezuma Creek and the S: <br />152.4 to 164.0), and two nea <br />the San Juan and Mancos r <br />230.6). One YOY Colorado <br />TL), was collected in 1988 <br />were taken in 1989. These w <br />of YOY Colorado squawfis <br />River drainage. <br />Between 20 March and 5 <br />corded 18 adult razorback ; <br />individuals; six were recaptt <br />south shore of Lake Powell n <br />ramp at Piute Farms Marini <br />were ripe; had well-tubercul <br />fins, and expressed milt whet <br />sure was applied. Abdomen <br />were distended and they ap <br />In 1988 (20 to 30 March), <br />suckers, half of which were <br />ture (expressed milt or api <br />collected at the Piute Farm., <br />Six of the 10 specimens were <br />1987 sample. This concentrr <br />a spawning aggregation (M <br />1987) or staging prior to ., <br />spawning site. <br />On 25 April 1988, a ri <br />razorback sucker (571 mm <br />RK 146.7 near Bluff, Uta <br />record of this species from I <br />San Juan River. No larval I <br />found in the 292 collection: <br />our survey. <br />The rediscovery of adult <br />presence of several age cla <br />tion of its successful spawl <br />River reconfirmed the spe <br />ponent of the ichthyofauna <br />The presence of razorback, <br />of the San Juan River 147 <br />Lake Powell verified its s <br />the fish fauna of the San <br />lection of a reproductively <br />Bested that the species m2 <br />riverine portion of the & <br />findings reinforced the imp <br />River drainage to the cont <br />rare species. Additional si <br />locate spawning sites and