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. DRAFT . reading at 8:56 am, but we believe that the lowest flow of the morning ocnlrrpd about 8:00 am. The maximum RWL of 885 rom was recorded at 3:50 pm. The total observable change in RWLwas 463 rom or 18.2 inches. . The minimum and maximum observable flows at Island Park were each approximately one hour earlier than predicted by BOR hydrologists. A minimum of 1500 cfs was predicted at 9: 00 am, but the observed minimum occurred about 8: 00 am. A maximum of 3900 cfs was predicted at 5:00 am, but the maximum observed was at 3:50 pm. Arrival time of flows at Rainbow Park may have been influenced by ice conditions. The total effective increase in flow of 2400 cfs was seen as an approximately 18-inch change in water level. . All three fish responded to the increase in flow stage. The most dramatic response was by razorback sucker OR-3234. The movement by the fish is depicted in Figure 13, and that movement related to flow is shown in Figure 19. When first contacted, the fish was relatively sedentary in an ice-covered slackwater. The fish moved upstream and into the main current over the course of the 12-hour observation period. The greatest movement was seen when the sudden increase in flow stage was accompanied by movement of large masses of ice. This occurred between 1000 and 1500 hours when flows increased from about 2500 to 4000 cfs. . . The two Colorado squawfish (OR-3235 and OR-3236) responded similarly to the increase in flow (Figures 12). Both fish were located under a solid sheet of ice during the entire observation period. The majority of their movement occurred between 1000 and 1300 hours, when flows increased from about 2500 to 3500 cfs (Figures 20 and 21). In this case, both fish moved with the arrival of large ice masses that washed beneath their ice cover. Our direct observations of these fish moving from the path of an oncoming ice mass was positive evidence that these conditions result in an energy expenditure by the fi sh . . We believe that low flow during cold air temperatures (below 0 C) induces ice formation in shallows along shorelines and over sand shoals. A subsequent increase in flow dislodges and transports this ice downstream. This combination of factors imposes a physical impedence to the fish when they are forced to dodge the oncoming masses of ice. Further analyses need to be performed on these data to identify the flow scenarios that create these conditons. . 7.0 WINTER F'ID'l RECOMMENDATIOOS 7.1 INSTREAM FI& INCREMENTAL METHODOLOGY . At this time (June 15, 1988), Phase I (Development of preliminary HSI Curves by BIOjWEST) is complete. Review of these curves and an initial run with PHABSIM data from selected stations will be conducted in late June and early July. OUr findings in this winter habitat study reveal new variables and different ways of handling old variables that need further consideration before proceeding with IFIM. We believe that instream structure (i.e. sand shoals, islands, etc.) needs to be considered. Also, we feel confident that the fish are using primarily the bottom third or so of the water column, and that use of mean . 35 .