9404 - Laserfiche WebLink

Home Browse Search

Movements by G. cypha within the LCR.---Our results 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 21; Fig. 1--2b)). In our analyses, river reaches were more extensive, and only encompassed those RKM within which G. cypha was active (i.e., 0--14.9). The confluence has often been considered a staging area for G. cypha (R. R. Miller, GCNP report, 1975, unpubl.; R. D. Suttkus, G. H. Clemmer, C. Jones, and C. R. Shoop, GCNP report, 1976, unpubl.; C. 0. Minckley, unpubl. field notes, 1977). Extent of G. cypha's movement within the LCR was not clarified until September 1977, when three large individuals (278--295 mm TL) were captured 12.8 RKM above the confluence (C. 0. Minckley, unpubl. field notes, 1977). From these data, and from AZGF monitoring efforts in spring 1987--1990 (C. 0. Minckley, unpubl.), it was believed that G. cypha actively moved into the LCR in spring (i.e., April/May) to reproduce, then quickly returned to the mainstem. Greater numbers of G. cypha at the confluence during spring of 1992 support an hypothesis of staging prior to upstream movement. Downstream (i.e „ postreproductive) movement also clearly occurred, but spanned a long period and was diffuse. Movements between LCR reaches during a given sampling period were negligible, suggesting temporal closure during periods of sampling. There was no evidence of explosive or extensive reproductive movements. Our results indicate population stasis within reaches, particularly summer through winter, suggesting that G. cypha is more of a resident component of the LCR than previously imagined. These observations support similar data collected by Karp and Tyus (1990) in the Yampa River. There, G. cypha remained in or near specific eddies for extended periods, and even returned to the same eddy during the spawning season in different years. It could not be ascertained whether individual chub deposited eggs in the eddies or simply used them for staging, resting, or feeding. Habitat use.-- rata on habitat use by G. cypha are primarily anecdotal and --,servational. 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 1991:150). Similarly, Kaeding et al. (1990) noted that commonality among G. cypha habitats is not great depth, but dynamic flow vectors that result from water moving rapidly among large, angular boulders and shoreline rock outcrops. Within other areas of the Colorado River, G. cypha often associates with large-scale riprap material from riverside railroad and highway construction (Kaeding et al., 1990). Karp and Tyus (1990) argued that eddy habitat was crucial to 10