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` REPORT OF THE HIOTECHNICAL StJBCaMMITTEE Introduction and Overview The Hiotechnical Subcommittee, and interagency working group, was organized in May 1984. Its task was to determine the habitat requirements of the endangered Colorado River fishes--those habitat characteristics that are essential to the survival of these species. During the past several months, the subcommittee has been cooperating with the Fish and Wildlife Service in the development of a complex computer model of the habitat of the Upper Colorado River Hasin endangered fishes. The model consists of several components--actually individual models that are interfaced with one another and thereby function to predict the availability of habitat for endangered Colorado River fishes under past, present, and possible future conditions of water development in the basin. Component models include a hydraulic model tHYDROSS) that predicts discharge conditions under various potential water-development scenarios, a temperature model that predicts river temperatures under these scenarios+ and a physical habitat simulation model (PHAHSIM) that uses outputs from the previous models to predict the availability of habitat for endangered fishes. The predictive ability of the habitat simulation model is therefore directly related to the predictive ability taccuraty) of the hydrology and temperature models. In January 1985 the Hiotechnical Committee was given the responsibility of critically analyzing the PHAHSIM model relative to the model's ability to predict flow-related changes in habitat for the endangered Colorado River fishes. The specific objectives of this analysis as established by the committee, were as follows: i) to identify the "data gaps" (major deficiencies) evident in the modeling effort; 2) to identify approaches to testing/validating the model; 3) to identify data/research needs; 4) short-term implementation of ESA Section F; 5) luny-term implementation of ESA Section F; 6) Conservation funding; and 7) future Biological Sub-committee activities. This document describes the results of that analysis. Major Deficiencies ADDITIONAL CONCERN 5. The interagency effort has resulted in the development of a flaw/habitat model; however, there are other important environmental parameters that--although not flow-related (e. g.+ cantaminants+ competitive spp,, movement barriers)--might have important effects on endangered fishes. These factors must be included or assessed if they are found to be important to the maintenance and development of populations of endangered fishes. RECOMMENDATION: Testing/validation of the modelfrequires testing of the following hypothesis: Nanflaw-related characteristics of the environment have important effects on the populations of endangered Cnlorado River fishes. RECOMMENDATION: Data/research needed to test the above hypothesis include the following: i