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24 COPEIA, ] 996, NO.1 DOUGLAS AI' TABLE 5. POPULATION EsT[MATES FOR ADULT Gila CYPha [N THE LITTLE COLORADO RIVER, BASED UPON PREVIOUS AND CURRENT RESEARCH (Conf!. = conf!uence area; All = entire LCR). period and was diffuse. Movements between LCR reaches during a given sampling period were negligible (Table 4), suggesting temporal closure during periods of sampling. No evi- dence of explosive or extensive reproductive movements was noted (Table 3; Fig. 3B). Table 3 primarily reflects population stasis within reaches, particularly summer through winter. These data suggest G. c)'pha is more of a resident component of the LCR than previ- ous]y imagined. Our observations of stasis by G. cypha within the LCR support similar data col- lected by Karp and Tyus (1990) in the Yampa River. There, G. c)pha remained in or near spe- cific eddies for extended periods and even re- turned to the same eddy during the spawning season in different years. It could not be ascer- tained whether individual chub deposited eggs in the eddies or simply used them for staging, resting, or feeding. cypha in the Yampa Riv< eddies and runs were sil tant in the B]ack Rocks ar tion, CO) (R. A. Valdez a Am. Fish. Soc., Bonnevil pub!.). Adult G. c)'pha ar (fig. 5 of Valdez and Clt daylight hours in the LCI waters along cut banks 1 etation (primarily reeds). crops, or in deeper pools are active during crepus. evening (C. O. Minckle: Douglas and P. C. Marsl Greater numbers of G the Salt Canyon reach (T: to Powell Canyon reach. least two alternative hyp< itat complexity in the S, greater numbers of large run interfaces, and dee residency of G. c)'pha w natively, those G. c)'pha 1 may literally stack withi[ either to a physical barr a chemica] one produCt other chemical content. Year Month Area Method Estimate Researcher(s) 1982 May All Multiple Census 7-8000 Kaeding and Zimmerman' 1987 May Conf!. 5783 C. O. Minckler" 1987 May Conf!. Multiple Census 1800 Kubly< 1988 May Conf!. 7060 C. O. Minckleyb 1988 May Conf!. Multiple Census 2900 Kubly< 1989 May All Multiple Census 25000 Kubly< 1992 May Conf!. Multiple Census 1320 Douglas and Marsh" 1992 May All Multiple Census 4346 Douglas and Marsh" 1992 May All Multiple Census 4602 Douglas and Marsh' . L. R. Kaeding and M. A. Zimmerman. USFWS Final Report. [982. unpub!. (Special Collections. Hayden Library. Arizona State University. Tempe). . C. O. Minckley, AZ/NM Chapter, Amer. Fish. Soc. Proc., [989. unpubl. (Special Collections. Hayden Library. Arizona State University. Tempe). , D. M. Kubly. Bureau of Reclamation Draft Report, 1990, unpub!. (Special Collections, Hayden Library. Arizona State University. Tempe). d Appendix I. . Appendix 2. (monthly for LCR)]. Although results from a model utilizing 19 months of data should be superior to an average of those data, any such long-term estimate must be viewed skeptically, given the violations of demographic and tem- poral closure mentioned earlier. Movements b)' G. c)pha within the LCR.-Results in Table I contrast with those of Kaeding and Zimmerman (1983), who found no consistent relationship between catch rate and river reach within the LCR [where river reaches were 5-km increments, beginning at RKM 2 and ending at Blue Springs (RKM 2]; Fig. 2B)]. In our anal- yses, river reaches were more extensive and only encompassed those RKM within which G. c)pha was active (i.e., 0-14.9). The confluence has often been considered a staging area for G. 0pha (R. R. Miller, GCNP report, 1975, unpub!.; R. D. Suttkus, G. H. Clemmer, C. Jones, and C. R. Shoop, GCNP report, 1976, unpub!.; C. O. Minckley, unpub!. field notes, 1977). Extent of its movement with- in the LCR was not clarified until Sept. 1977 when three large individuals (278-295 mm TL) were captured 12.8 RKM above the confluence (C. O. Minckley, field notes, 1977, unpub!.). From these data, and from AZGF monitoring efforts in spring 1987-1990 (C. O. Minckley, unpubl.), it was believed that G. c)pha actively moved into the LCR in spring (i.e., April/May) to reproduce then quickly returned to the main- stem. The fact that greater numbers of G. c)pha were found at the confluence during spring of ] 992 (Table 1; Fig. 3B) supports an hypothesis of staging prior to upstream movement. Down- stream (i.e" postreproductive) movement also clearly occurred (Table 3) but spanned a long Glen Can)'on Dam and Gih term residency by G. C)pJ ticularly summer throu~ fact, many adults appan the LCR, effectively usi refugium. Two hypothe commodate these data. 1 is a pre-dam componen tory. The other proposl alteration. It is unclear both are untestable in tl Long-term residency ways been an aspect of We know, for example, the pre-dam LCR durin~ 19] 4: 127; Carothers < However, its duration 0 residency has always be c)'pha's natural history, ture data simply define evolutionary time. An alternative hypotl thermal regime of the cypha to adjust its life modates lower mains marily through avoi residency within the anecdotally suppor movements into/fr accomplished by I Habitat use.-Data on habitat use by G. c)'pha are primarily anecdotal and observational. Adults characterize whitewater reaches, where they occupy deep, swirling eddies along canyon walls or concentrate in zones of turbulence near boulders and submerged rocks (Minckley ] 991: 150). Similarly, Kaeding et a!. (1990) noted that commonality among G. c)pha habitats is not great depth but is instead the dynamic flow vectors that result from water moving rapidly among large, angular boulders and shoreline rock out- crops. Within other areas of the Colorado Riv- er, G. c)pha often associates with large-scale rip- rap material from riverside railroad and high- way construction (Kaeding et aI., 1990). Karp and Tyus (] 990) argued that eddy hab- itat was crucial to breeding requirements of G.