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. DRAFT . ice cover. Radiotagged squawfish GR3422 (Figure 11) illustrates this point; movement by this fish was to three favorite spots within a small area and restricted habitat type. The three locations used by this 570-mm long fish were 0.4, 1.2, and 0.3 feet deep; water depths that would not be expected to be used by an adult during daylight hours. . In contrast to the stable ice condition described above, two radiotagged squawfish observed under unstable ice (Figure 12) changed position frequently in response to movement of large ice masses. These fish were monitored during all six tracking trips from December, 1987 through March, 1988 in the Rainbow Park area. During the 8-hour period on January 7, 1988, in which flows increased from 1500 to 4000 cfs, local movement by these fish was extensive in an apparent effort to escape the large masses of ice moving through the entire water column. Squawfish OR3235 was positioned at the upstream edge of the path of ice flow and exhibited gross movement of only 48m and net movement of 10 m. However, squawfish OR3236 was positioned further downstream in the path of the ice flows, and exhibited gross movement of 145 m and net movement of 30 m. Nearly every movement by these fish was in direct response to the arrival of a large ice mass, visable on the surface and audible as loud popping and cracking sounds beneath the ice occupied by the two fish. In late January, squawfish OR3236 twice moved downstream about 1 mile from this location and returned, only to be found dead in mid-March in a shallow side channel, apparently from predation by a raptor, i.e. bald eagle. Simultaneous observations of razorback sucker OR3234, located 0.3 mile upstream, show the same movement response to the ice flows. . . . understanding the mechanism which created these unstable ice conditions is important to this analysis of winter habitat needs of the two endange red fishes. It is believed that thick heavy layers of ice first formed along shorelines and shallow areas during low river flows. This ice was subsequently dislodged and transported downstream by rising water levels. Movement of these large ice masses through fish habitat forced the fish to move frequently and expend unknown amounts of energy. The effect of this energy expenditure on survival, growth, and reproductive potential is unknown. Also, the frequency of this phenomenon at any point along the river is unknown, but it was observed several times from early January through early February, 1988 and probably occurred every time a low flow cycle was followed by high flow during a cold period. . . 6.1.4.2.2 Razorback Sucker . Razorback OR3234 also moved extensively in response to the movement of ice masses through the Rainbow Park area (Figure 13). Gross movement of this fish during 8 hours was 246 m and net movement was 40 m. This fish moved to a total of 20 locations, which extended across the entire river channel, during this period of rising water level and ice transport. . In contrast to the above condition, razorbacks OR3229 (Figure 14) and OR3226 (Figure 15) exhibited little movement under stable ice. Each occupied only two favori te spots in a pattern not unlike that of the fish in ice-free water. However, unlike the squawfish under stable ice, all razorbacks observed 32 .