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SUBADULT HUMPBACK CHUB IN THE COLORADO RIYER 271 Table I. Definitions of shoreline types Bedrock Any rock that is in its original location and has not been transported or broken up by any means. This includes shear walls and laterally or vertically emerging ledges Cobble Rocks transported by main channel activity that are characteristically well rounded and imbircated. They may show some embeddedness Debris fan Debris, predominantly boulder, transported from a tributary during a flooding event. It is characterized by boulders with some degree of embeddedness, intermit- tent sand beaches, and a small percentage of gravel. The angle of repose is generally flatter than that of talus. The boulders are more rounded as inferred by the process of transportation Sand Minimum length of 50 m of predominantly exposed sand. Beaches can have very steep banks or be very flat Talus Colluvium, predominantly boulder, deposited by rockfall or rockslide activity on the canyon walls. It is characteristically not embedded and has a steeper angle of repose than a debris fan. May have some intermittent sand. Debris is more angular as inferred by its process of transportation Vegetation This can be rooted or inundated vegetation. The vegetation along the shoreline must be in or directly over the water on the shoreline. Vegetation may have intermittent stretches of other shoreline types " quantified physical habitat conditions for six shoreline types within two reaches (reaches 1 and 2). Shoreline type designations, based on differences in structure and geomorphology, included bedrock (shelves and vertical cliffs), cobble, debris fan, sand, talus and vegetation (Table I). Second, we used stratified random sampling to estimate relative fish densities in all six shoreline types within all reaches (reaches 1, 2 and 3). Reach 3 was added to this analysis midway through the study after habitat data collection was completed, hence we were only able to obtain fish capture data from reach 3. Finally, data were collected on discharge variability and how habitat changed as a consequence of flow variation was estimated. Both physical measurements and fish sampling were conducted over the range of discharges from Glen Canyon Dam that represented interim flows. Data collection was conducted for 1-2 weeks per month from October 1990 to November 1993 (except Decembers) and in July 1994 (Valdez and Ryel, 1995). To determine geomorphic differences among reaches, we calculated total availability of shoreline types, total riffle area and width-to-depth ratios of reaches 1, 2 and 3. To quantify differences in habitat at both spatial scales (reach and shoreline), water depth, velocity and cover along shorelines were measured within reaches I and 2. Because reach 3 was added midway through the study, shoreline habitat data were collected in reaches I and 2 only. Physical habitat sample sites were stratified among reaches I and 2 to include all shoreline types but were randomly chosen within reaches. Because we were logistically limited in where, when and how often certain data could be collected, sample numbers among reaches and shoreline types were not balanced (Table II). Fish sampling was stratified among the six shoreline types and randomly chosen within all three reaches. A total of 664 electrofishing efforts conducted (Table III) were used to summarize habitat conditions, however only 173 electrofishing samples that had spatially concurrent habitat measurements were used to analyze direct associations of fish with habitat. Table II. Number of transects measured among reaches and shoreline types Reach Shoreline type Total Bedrock Cobble Debris fan Sand Talus Vegetation I 4 2 3 Combined 7 2 7 9 7 2 9 11 3 14 7 7 14 9 7 16 40 29 69 ~ 1998 John Wiley & Sons, Ltd. Regu/. Rivers: Res. Mgmt. 14: 267-284 (1998)