7422 - Laserfiche WebLink

Home Browse Search

. DRAFT. . frequently subjected to large masses of moving ice through the ice-covered area often used by the fish. 6.1.1.2 Razorba~k Sucker . Significantly greater movement was also seen for razorback suckers in 1987-88 (16.91 m,lhr) than in 1986-87 (28.72 m,lhr) (Table 3). However, unlike the movement by squawfish, movement by razorbacks was greatest when the fish had no overhead ice cover (32.25 vs 12.38 m,lhr). This is the case because the majori ty of razorbacks radiotagged for 1987-88 occupied regions that were subject, to either freezing and thawing (Rainbow Park) or to ice jams at the edge of the ice pack (Split Mountain to Dinosaur National Momunent Visi tor Center). Thus, although the fish had no immediate overhead ice cover, their proximity to the ice pack and to moving ice masses caused greater movement. . . To test this hypothesis, only observations during periods with river ice were used. When movement was compared for fish under ice cover (12.59 m,lhr) with fish in the absence of ice cover (35.77 m,lhr), movement by razorbacks in the absence of ice was signficantly greater. This is opposite to the movement response by Colorado squawfish to ice cover, and is perceived as a function of primarily two factors: (a) lack of behavioral response to ice as cover, and (b) movement of fish at the edge of the ice pack to avoid ice masses. The former factor 'a' explains the similarity in movement by razorbacks in the absence of ice cover in 1986-87 (15.36 m,lhr) and under ice cover in 1987-88 (12.59 mjhr). This suggests that the razorback does not significantly alter its behavior following ice formation. However, the lesser degree of movement in 1987-88 may also be partly attributed to the confining effect of frazil ice on the majority of radiotagged razorbacks between RMI 308.8-318.8. Conversely, movement of fish at the edge of the ice pack (fish in the absence of direct ice cover) near Razor Island and at the partially frozen region at Rainbow Park exhibited a high degree of movement (35.77 m,lhr) in response to large masses of floating ice. This was similar to the response seen by Colorado squawfish to avoid these ice masses moving through their habitat. . . 6.1.2 Long-Range Movement . Long-range movement was associated with fish that changed position in the river significantly. This movement was considered transitory, between habitats located some distance apart. Although long-range movement was generally documented as occurring between tracking trips, it was also observed during 2- hour and 24-hour monitoring. All long-range movement by adult Colorado squawfish and razorback suckers during both years of the study were confined to the study area. The sites of release and relocation of each radiotagged fish are presented in Table 4. Net and total movement figures do not include the distance from the release site to the first radio contact site because most of the fish made substantial movements from the point of release before settling into a localized area. . 6.1.2.1 Colorado Squawfish . The mean distance moved by Colorado squawfish between the release site and the location of first radio contact during year 1 was 6.2 miles with a range of 0.1 25 .