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<br />, Table 8. Numbers of Bottom Organisms per Square Foot Collected at
<br />Different Water Velocities in Stream Riffles
<br />
<br />various reaches of the same stream. Part of this variation is due to the
<br />
<br />diversity of species, their life histories, and their habitat require-
<br />
<br />ments, In addition, ecological factors such as water temperature or
<br />
<br /> Source
<br />Water velocitva Pearson
<br />(em/see) (feet/see) and coauthors Surber Kennedy
<br />15-31 0.5-1.0 53 99 ~
<br />34-46 1.1-1.5 90 l48b 88lb
<br />49-61 1.6-2.0 120b 115 484
<br />64-76 2.1-2,5 89 l5~ 289
<br />79-91 2.6-3.0 105 125 171
<br />95-107 3.1-3.5 65 3390
<br />110-122 3.6-4,0 62
<br />
<br />chemical components that affect productivity of the stream vary and af-
<br />
<br />feet abundance (Knight, 1965). Riffle habitats are important in producing
<br />
<br />bottom organisms (Hill, 1965; table 9). However, different groups of or-
<br />
<br />ganisms are found in slower water. The substrate composition can also be
<br />
<br />important in the distribution of bottom organisms (Sprules, 1947; table 10).
<br />
<br />It is not possible to review fully the literature on the ecological re-
<br />
<br />quirements of bottom organisms. However, the preceding examples were used
<br />
<br />to provide some insight into the factors affecting distribution and abun-
<br />
<br />dance of macroinvertebrates.
<br />
<br />Drift of bottom organisms has been shown to be important to the ecol-
<br />
<br />Source: H, D. Kennedy, Seasonal Abundance of Aquatic Invertebrates
<br />and Their Utilization by Hatchery-Reared Rainbow Trout, Bureau of Sport
<br />Fisheries and Wildlife, Technical Paper 12 (Washington, D.C., U.S. Depart-
<br />ment of the Interior, 1967); L, S. Pearson, K, R. Conover, and R. E. Ssms,
<br />"Factors Affecting the Natural Rearing of Juvenile Coho Salmon During the
<br />Summer Low Flow Season," Unpublished manuscript (Portland, Oreg., Fish
<br />Commission of Oregon, 1970); E. W. Surber, '~ottom Fauna and Temperature
<br />Conditions in Relation to Trout Management in St. Mary's River, Augusta
<br />County, Virginia," VirRinia Journal of Science vol. 2 (1951) pp. 190-202;
<br />as reported in R. D. Giger, Streamflow Requirements of Salmonids, Final
<br />Report, Anadromous Fish Project AFS-62-1 (Portland, Oreg., Oregon Wildlife
<br />Commission, 1973).
<br />
<br />aSurber recorded surface velocity; depth of measurement not specified
<br />in other studies.
<br />
<br />ogy of stream-dwelling fish (Waters, 1969). This drift is another complex
<br />
<br />ecological phenomenon about which generalizations are difficult to make.
<br />
<br />However, bottom organisms may exhibit different patterns in diel and sea-
<br />
<br />sonal periodicity in natural drift that varies by species, streamflow,
<br />
<br />water temperature, and perhaps other ecological variables. The numbers
<br />
<br />of organisms in the drift and on the bottom may differ by species in the
<br />
<br />same location at the same time (Pearson, 1967; Pearson and Franklin, 1968;
<br />
<br />figure 1). In addition, comparisons of the same groups of bottom organ-
<br />
<br />b
<br />Underlined data indicate the mode in distribution of bottom organisms
<br />as related to water velocity.
<br />
<br />c
<br />Inadequate sample size.
<br />
<br />isms between locations demonstrate that generalizations about the rela-
<br />
<br />tionship between organisms on the bottom and organisms in the drift are
<br />
<br />risky (figures 1 and 2).
<br />
<br />Changes in the flow and water temperature in the Green River after
<br />
<br />the closure of Flaming Gorge Dam also changed the distribution and species
<br />
<br />composition of macroinvertebrates. Pearson, Kramer, and Franklin (1968)
<br />
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