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believed that the preliminary flow recommendations that we propose will also benefit <br />the recovery of this rare species. Comments received on drafts of this document, and <br />our subsequent responses, have been incorporated into the text. Appendix E provides a <br />list of persons who commented on drafts of this report. <br />A Strategy for Determining the Flow-habitat <br />Requirements of the Endangered Fishes <br />The fundamental and obvious component of the aquatic ecosystem and of the <br />habitats of fishes is water. However, quantifying the amount of water needed to sustain <br />a fish population of a particular size is not an easy task. In an effort to understand the <br />important factors that control the size of fish populations, numerous studies have <br />attempted to relate population size to river discharge and other variables of the aquatic <br />environment. Results of these studies have most often been less than definitive, with <br />few important correlations being found between presumed important environmental <br />variables and the size of the populations themselves (see for example Orth 1987). These <br />and other studies have clearly shown that a complex array of interacting variables affects <br />the size of fish populations, and that the relative importance of these variables may <br />change over time and space. Thus, there can be no simple, universal formula to <br />describe the. relation between discharge or any other environmental variable and fish <br />population size (also see Orth 1987). But the general lack of correlation with discharge <br />should not be taken to mean that discharge has no important effect on the size of fish <br />populations. In many instances, the carrying capacity of a river for a particular fish <br />species may be less than that allowed by the volume of water alone--the actual physical <br />2