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916 COPEIA, 1998, NO.4 adults congregate at upstream ends of cobble bars to spawn (McAda and Wydowski, 1985). Postreproductive adults remain in flatwater or eddies near margins of strong currents, gener- ally in water at least 1 m deep. Young often con- gregate downstream or on riffles and along shoreline of flatwater reaches. Chart and Ber- gersen (1992) suggested adult movements are size-related, with larger individuals more sed- entary than those 300-400 mm TL. They also suggested that adult C. latipinnis occupy a defin- able home range. Individuals are considered adult at 300-400 mm TL (Minckley and Hol- den, 1980); maximum size recorded in this study was 661 mm TL. Xyrauchen texanus was also historically distrib- uted throughout the Colorado basin. It was common in the lower basin (Kimsey, 1957) and in reservoirs created by main-channel dams. It was uncommon and declining in the upper ba- sin by 1950 [Hubbs and Miller, 1953; Vanicek, 1967 (citing early 1960s agency reports)]. Hol- den (1973) collected X. texanus only from mid- dle and lower sections of the upper basin and again noted its scarcity. It was also recorded as sparse within Grand Canyon and areas imme- diately north. Smith (1959) called X. texanus ". . . rare, or possibly just difficult to collect in Glen Canyon, since extensive collecting turned up only two immature (i.e., YOY) specimens" (Glen Canyon, immediately upriver from Grand Canyon, is now inundated by Lake Powell). Many researchers (Minckley et aI., 1991:310; this study) contend X. texanus was never abun- dant in Grand Canyon, regardless of its current conservation status. Genetic variability within remnant Colorado River populations of X. texanus is distributed in a north-south cline (Dowling et al., 1996a) sim- ilar to that recorded for abundance. More northern populations (i.e., upper Green and Yampa Rivers, upper Colorado River) exhibited reduced variability, whereas the most extant southern population (i.e., Lake Mohave, AZ) was highest. Geographically intermediate pop- ulations (Le., Lakes Mead and Powell) were themselves intermediate in haplotype diversities (with Powell populations greater than Mead). Over evolutionary time, this species was pan- mictic throughout its range. Hybrids between C. latiPinnis and X. texanus occur in small numbers and have long been rec- ognized. Jordan's (1891) description of X. un- compahgre was based on a C. latipinnis X X. tex- anus hybrid. Hubbs and Miller (1953) exam- ined eight putative hybrids (two from upper Colorado and six from upper Green Rivers) and noted morphological intermediacy in lateral- line scale count, and a much abbreviated but distinct nuchal keel. Hybrid intermediacy was also reported by Vanicek (1967:45), who subse- quently collected 16 putative hybrids from the Green River following closure of Flaming Gorge Dam (Vanicek et aI., 1970). Holden (1973) col- lected 40 putative hybrids and 53 X. texanus throughout the upper basin, usually associated with one another in quiet backwater areas. Hy- brids in upper Green and lower Yampa Rivers were attributed by Tyus and Karp (1990) to an abundance of C. latipinnis, a paucity of X. tex- anus, and a temporal! spatial overlap in their spawning. Smith (1992b) listed hybrids of these two species as occurring broadly across drain- ages. The present study was a four-year, localized study with three goals: to estimate population numbers and survival probabilities of C. latipin- nis and X. texanuswithin the Little Colorado Riv- er (LCR) area of Grand Canyon; to evaluate their seasonal and yearly movement patterns within that area; and to determine relative abundance and distribution of potential hy- brids. MATERIALS AND METHODS Study area and data collection.-Our study was confined to the LCR and its confluence with the mains tern Colorado River, 99 river km (RKM) below Glen Canyon Dam. The study area, in both Grand Canyon National Park (GCNP) and the Navajo Nation (Coconino County, AZ), is described and mapped in Douglas and Marsh (1996). Base camps were established in the LCR gorge at 0.6,3.1, and 10.8 RKM upstream from the confluence. Biologists worked at each camp during 49 six- to 14-day trips at approximately monthly intervals from July 1991 to June 1995 (Appendix). Fishes were captured with hoop and trammel nets (the latter primarily at con- fluence; net dimensions provided in Douglas and Marsh, 1996). Effort was recorded as num- ber of net-hours fished. All captured fishes were identified, measured (TL to nearest mm), weighed (nearest g), and sex determined. Big- river endemics greater than 150 mm TL (= adults) were injected with passive integrated transponder (PIT) tags (Prentice et aI., 1990) and released near points of capture. Capture matrices.-Adults were classified as newly tagged fish, recaptured fish, or those with old tags. The first group represented fish PIT- tagged by Arizona State University (ASU) per- sonnel at time of capture. The second group ~ '\