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kAb <br />Transactions of the American Fisheries Society 120:339-345, 1991 <br />Movements of Adult Colorado Squawfish during the <br />Spawning Season in the Upper Colorado River <br />CHARLES W. MCADA AND LYNN R. KAEDINGI <br />U.S. Fish and Wildlife Service, Colorado River Fishery Project <br />529 25th Road, Suite B-110, Grand Junction, Colorado 81505, USA <br />Abstract. -Colorado squawfish Ptychocheilus Lucius spawned in widely separated areas through- <br />out the 350-km section of the upper Colorado River upstream from Lake Powell, Utah, as evi- <br />denced by the movement of radio-tagged adults during the spawning season and the later capture <br />of larvae. With one exception, tagged fish remained separated from each other during the spawning <br />season. Distances moved by tagged fish were not related to fish size or location of initial capture <br />along the river. Movements were generally shorter (mean, 23.2 km) than those reported for this <br />species in the Green River basin, in part because of important habitat differences between the two <br />rivers. Most tagged. Colorado River fish were found near their initial point of capture after the <br />spawning season. <br />The Colorado squawfish Ptychocheilus lucius, a <br />large piscivorous cyprinid endemic to the Colo- <br />rado River basin, has been presumed to make sea- <br />sonal, often long-distance migrations to discrete, <br />widely separated river reaches to spawn; its larvae <br />are believed to drift to nursery areas far down- <br />stream (Tyus 1986). Such life-history character- <br />istics have implications for management to pro- <br />tect and enhance the habitats and populations of <br />this endangered species. Blockages of fish move- <br />ment, for example, can decimate populations of <br />obligate migratory fishes, as demonstrated by Co- <br />lumbia River dams and Pacific salmons Onco- <br />rhynchus spp. (Netboy 1974). For this reason, it <br />was important to determine whether the life his- <br />tory proposed by Tyus (1986) for Colorado <br />squawfish in the Green River basin is generally <br />applicable to this species. The objective of our <br />study was to describe the movements of adult Col- <br />orado squawfish during the spawning season in the <br />upper Colorado River. <br />Study Area <br />The study was conducted in the 350-km reach <br />of the Colorado River between Lake Powell, Utah, <br />and Palisade, Colorado (Figure 1). Locations along <br />the river were demarcated as river kilometers (RK) <br />upstream or downstream from the confluence with <br />the Green River (RK 0). The study area was di- <br />vided into eight reaches (Figure 1) defined largely <br />by the occurrence of major tributaries, barriers to <br />upstream movement, or prominent changes in <br />'Present address: U.S. Fish and Wildlife Service, Yel- <br />lowstone Fishery Assistance, Post Office Box 184, Yel- <br />lowstone National Park, Wyoming 82190, USA. <br />river morphometry. Cataract and Westwater can- <br />yons were not sampled because of logistic diffi- <br />culties. Reach 8 is a short (4-km) segment of the <br />Gunnison River downstream from the Redlands <br />Diversion, a barrier to the upstream movement <br />of fish. <br />Methods <br />Larval fish. -Larval Colorado squawfish were <br />used to estimate the spawning period. We sampled <br />larval Colorado squawfish (6-24 mm total length, <br />TL; Snyder 1981) in reaches 2 through 7 during <br />July and August 1982 and from July to September <br />1983, 1984, and 1985. Colorado squawfish spawn <br />during these months in the upper Colorado River <br />(Haynes et al. 1984). Each of reaches 2-7 was sam- <br />pled at about 2-week intervals; reaches 1 and 8 <br />were sampled less frequently. We used 0.5-mm- <br />mesh seines (0.9 x 0.9 m) to collect larval fish <br />from low-velocity shoreline areas (e.g., backwa- <br />ters, eddies, pools) at about 8-km intervals along <br />the river. Collection of each sample required 5- <br />15 min. All larval fish collected were fixed and <br />preserved in 5% formalin and later identified and <br />counted at the Larval Fish Laboratory, Colorado <br />State University, Fort Collins. Colorado squaw- <br />fish larvae were measured to the nearest milli- <br />meter (TL). <br />We estimated hatching dates for individual Col- <br />orado squawfish larvae by back-calculation with <br />an equation developed by Haynes et al. (1985) for <br />the growth of age-0 Colorado squawfish in a <br />hatchery at about 20°C (Hamman 1981): <br />339 <br />AGE = -76.7105 + 17.4949 TL <br />-1.0555 TL2 + 0.0221 TV