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268 <br />of the year (from June through September), when access, streamflow, and water <br />quality are optimum for aquatic observation. Aquatic conditions thus are <br />seldom measured during periods of floods, annual high flows, extreme low flows, <br />channel icing, ice flow scouring, and debris jam breakups. Because many lim- <br />iting factors, whether imposed within the system or by the surroundings, will <br />usually exist during periods of no observations, the true (changing) state of <br />the system over time has not been determined. A valid understanding of the <br />environmental mix usually escapes us. Thus, the value of observed physical, <br />biological, and chemical variation that should predict fishery conditions is <br />low. <br />Past studies do demonstrate correlations and interadjustment between parts <br />of the aquatic system and also with the surroundings, but not the correlation <br />between the environmental variables, the environmental mixes, and fish <br />populations. <br />Structural Correlations <br />Leopold and Maddock (1953), in quantitative studies, showed a correlation <br />and interadjustment between stream discharge, sediment transport load, gradient, <br />width, and depth. Leopold and Miller (1954), Morisawa (1962), and Lubowe (1964) <br />compared inter-aquatic structural variables with the surroundings and stated <br />that stream gradient, stream width, length of stream, area of stream drainage, <br />water discharge, shape of drainage basin, and relief have consistent relation- <br />ships among themselves and with stream order within the same drainage complex. <br />Von Vertalanffy (1950) expressed the idea that systems in their responses <br />to the surroundings may be dominated by one type of external variable. The <br />trend, however, has been toward recognition of multivariable control in geo- <br />morphic systems (Weber 1958). The literature amply demonstrates that the <br />structural environmental components of a stream are influenced by the <br />surroundings. <br /> <br />r <br />Biological-Structural Correlations <br />Researchers differ in their findings as to what variables are the most <br />important in controlling fish populations, and the differences appear to depend <br />partly on the condition of the environments they studied. Cummins' (1966) ex- <br />tensive literature review found that no single factor has greater biological <br />significance in the stream than the physical nature of the channel substrate. <br />Schuck (1945), Inger and Chin (1962), and Ruggles (1966) found that stream <br />depth significantly affected trout populations. Saunders (1965), McNeil and