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95 , a few pages. However, it is clear that current methodologies do not take investigators have shown that territoriality is not exhibited, or at least into account the wide range of environmental factors on which information is reduced, in pool environments, demonstrating that water velocity is will be needed to ensure sound decisions on streamflow recommendations, tmportant in determining the distribution and carrying capacity of stream- In fact, several of the literature reviews have uncovered large gaps in dwelling sa~onids. Fish size also influences habitat selection and, in existing knowledge of the basic ecology of fish (e.g.. the Pacific North- general, large fish have large territories and occupy areas with a greater west River Basins Commission (1972) suggested research on requirements water velocity than those occupied by small fish, In addition. there are for rearing young salmonids, and Hooper (1973) suggested research on the differences in habitat selection by species; for example, rainbow trout effects of water flows on the drift rates of invertebrate organisms). usually are found in faster water than cutthroat trout, and brown trout Giger (1973) concluded that "improved understanding of the stream ecology generally require more cover than cutthroat trout. of juvenile salmonids is seen as a more important immediate goal, however, than efforts to develop procedures for making streamflow recommendations," The importance of overhanging cover and pools as habitat for trout has been reported by Weber (1959) and others. He reported that stream- Salmon ids flows below Grandby Dam on the Colorado River are only about 11 percent Although literature reviews have shown important gaps in available of average annual historical flows and that overhanging cover is lacking information on stream-dwelling salmonids, the behavior, ecologys and life during low streamflows. Weber reported that trout could be captured by electro-fishing in shallow pools (6 inches deep) at low flows if these r . ~ p < history of this group of fish has been intensively studied (Allen, 1969) and is now fairly well understood. Stream-dwelling salmonids are known to pools were near the water line with brush cover. He also was able to ~ L be territorial in their behavior (Allen, 1969; Edmundson. Everest, and Chapman, 1968; Giger, 1973; Hooper, 1973). The locations of the terri- demonstrate that trout would occupy reaches of the stream if cover was ~ ~ ~ tories are influenced by the availability of drifting food (Chapman, 1966; collected and, in approximately one month, all of these piles contained , , ~ ~ 1 , , . provided. He placed five brush piles where fish had not been previously Waters, 1969), with the more dominant fish occupying the area with the trout. Numerous papers in the literature support the importance of cover greatest drift, Coupled with the availability of food is the spatial re- quirement of salmonids (Allen, 1969; Chapman, 1966). Giger (1973) re- for trout populations even more strongly than this example from the Colo- rado River. However, it is quite clear that cover is directly related to ported that his review of the literature demonstrated a positive, fairly linear relationship between fish size and average area of streambed per fish. These food and spatial requirements are influenced by water veloc- streamflows because. at the extremes, streambank cover can be eroded by excessive flows and the water may recede from cover at low flows. Lewis (1969) demonstrated that water velocity accounted for 66 per- ity and cover (Chapman, 1966). Furthermore. Chapman and other . cent of the variation in numbers of brown trout and that total cover accounted for 59 percent of the variation in numbers of rainbow trout. ~ ~