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' Winter 1, gravel (MM) was often used in backwater habitat, even though this was a zero-velocity area. In Winter 2, this substrate type was used very little, probably because the backwater area used in winter 1 was not 1 accessible. Substrate use was evenly distributed in the other habitat types. Sand was the predoninant substrate used by fish during the fall (Table 9). ' Habitat use over time Habitat use patterns over time were examined by recording the number of observations in each study area according to habitat type used on each trip. This was dome to determine if habitat use differed by study area or charred in response to season, discharge or weather conditions. During Winter 1 in the Gaverrnment Bridge study area, the majority of ' habitat use was in the backwater habitat at F441 95.7. No shifts in habitat use were noted in fish using this backwater. However, the one fish not using this backwater alternated habitat use from embayment to run between January 5- 10 and January 19-24 (Table 10). Use of run habitat coincided with lowest flaws (250-300 cfs) and coldest winter temperatures during Winter 1 (Figure 16). In the Maybell study area, habitat use during Winter 1 was evenly divided between embayments and runs. Again, use of run habitat' coincided with low flows and cold air temperatures. Run habitat was used exclusively on January 19-24, 1987. This shift to run habitat did not appear to be related to I changes in availability of habitat, since embayment areas were still accessible. Use of run habitat could be related to the presence of frazil ice. During this cold period, several squawfish were located under stationary frazil ice (0.1-4.7 feet thick), which was packed up beneath solid ice cover. Squawfish may have been attracted to habitats containing newly formed frazil ice (anchor ice broken free) because it contained or attracted food. Squawfish could feed directly on invertebrates but more likely would feed on small fish attracted to the small food items delivered by frazil ice. Turbid frazil ice often contained silt, pebbles, and aquatic invertebrates (mainly staneflies).' In the second year of the study, biweekly habitat use patterns of squawfish were analyzed from mid September to the end of June. In early September, squawfish in the Gwerrment Bridge study area used eddy, eubayment and shoreline habitat. In October through mid Novetnber run habitat was used predominantly. From late November through early December, backwater and erobeyn habitats were used most frequently. During this period, ice was beginning to form on these lows-velocity habitats,. From mid-December through ice-out squawfish were observed in run habitat almost exclusively, although other habitats were nearby and accessible. High use of run habitat in Winter 2 could be related to the generally lower flows and colder temperatures. During the spring (April-June) habitat use shifted to eddy and backwater habitat (Table 11). During the fall, from mid-September through November, 1987, habitat use in the Maybell stbdy area (FM 85-80) was distributed between eddy, eMbayment, pool, rum, and shoreline. During the remainder of Winter 2 until ice-cut, habitat use alternated between embayment and run much as it had during Winter 1 (Table 11). Again, the exclusive use of rum habitat appeared related to the ' coldest t?eoperatures in early January and February (Figure 17). During the spring, habitat use shifted to eddy, backwater, and shoreline. 1 35 1