1113 - Laserfiche WebLink

Home Browse Search

Electrofishing data were primarily taken in shoreline runs; radiotelemetry observations included more fish located in deep eddies and fewer from shoreline runs (Figure 3). The difference between the two methods apparently is due to bias in habitat types recorded for fish collected by electrofishing, caused by fish moving into the electrical field or being "herded" (Hynes 1970). The distributions of habitats recorded for both sources were tested by a Chi-square analysis, which indicated they were significantly different (P < 0.001). There was also a significant difference (P < 0.005) between corresponding substrates recorded for these fish (Figure 3). Analysis of variance (ANOVA) indicated that average depths recorded at capture locations of 91 Colorado squawfish (mean = 1.23, SD = 0.55) were significantly different (P < 0.04) than depths recorded for 244 observations of radiotagged fish (mean = 1.40, SD = 0.79), but corresponding velocities were not significantly different (P > 0.5). Habitat data obtained by fish radiotelemetry is assumed more accurate than that obtained by electrofishing because gear selectivity and lack of efficiency can be avoided. In addition, diet and seasonal habitat preferences can be obtained for the same fish. In large, turbid river systems where conventional fish collecting techniques cannot effectively sample all habitats (and fish cannot be visually observed), radiotelemetry may be the only tool available to obtain such information. HABITAT USE Colorado squawfish undertook spawning migrations each year, and exhibited homing (Tyus 1985) to two major spawning areas in the Green River P~sin (Figure 4). Their movement patter-s were useful in partitioning the habitat data into three seasons: migration, spawning, and "adult" (rer^ai^der of the year). No habitat use data were collected during the migration periods before and after spawning, when the fish were moving. During the July-August spawning period, radiotelemetry contacts indicated the fish were selecting deep pools or eddies, and riffles. The fish would remain in deep pools or eddies, abruptly move to cobble bars, then return. This behavior, similar to visual observations made for spawring northern squawfish (Beamsderfer and Congleton 1982), warranted the division of selected habitats into two apparent types: (1) a resting-staging habitat in pools or large shoreline eddies where the fish may find suitable resting and feeding habitat b:tween spawning forays or where males may gather around females until they are ready to deposit eggs, and; (2) a deposition-fertilization habitat in riffles, where males and females congregate, females deposit eggs, and the mils fertilize them. A comparison of spawning habitats between the Green River and its Yampa River tributary (Table 3) indicated that fish in both rivers utilized similar microhabitats, and the close agree~ent between years (Table 3) s~ygested that the division of spawning habitat relative to the behavior of the fish was proper. 149