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© 1990 by S.E.L & Associates Habitat Suitability Index Curves for Humpback Chub of the Upper Colorado River Basin Richard A. Valdez Paul B. Holden Thomas B. Hardy* BIO/WEST, Inc. 1063 West 1400 North Logan, Utah 84321 ABSTRACT. Habitat suitability index (SI) curves were developed for the endangered humpback chub (Gila cypha) using previously-collected mi- crohabitat data from the Upper Colorado River Basin. Data selection, par- titioning and pooling, as well as curve development were decided by consensus by a panel of species experts during two week-long workshops. The result was a total of 14 riverine SI curves associating four life stages (larvae, young-of-the-year, juvenile, and adult) with three microhabitat parameters (water depth, velocity, and substrate). The SI curves were developed to best fit actual field data, and modified by the experts ac- cording to biological judgment. The species experts classified these as "interim SI curves" and recommended application of only the adult curve set, recognizing that much information still needs to be gathered on the rare fishes of the upper basin. The process by which these SI curves were developed is recommended in dealing with large volumes of pre-existing microhabitat information scattered through many literature sources and reports. The concept of assimilating the data for evaluation by a panel of species experts was sound in that it allowed for a joint review by the experts without each investing large amounts of time to independently research the data. The idea of open workshops, in which experts and participants were given equal opportunity to express opinions, also worked well, although a third workshop was recommended to allow the experts to participate in generation of weighted usable area and evaluation of the streamflow to habitat relationships. KEY WORDS. Humpback chub, Gila cypha, habitat suitability index curves, Upper Colorado River Basin, microhabitat, Physical Habitat Sim- ulation, Instream Flow Incremental Methodology, Delphi technique, en- dangered species. T INTRODUCTION he Instream Flow Incremental Meth- odology (IFIM) is one of many meth- ods available to quantify the habitat of riv- erine fishes as a function of flow (Stalnaker * Present address: Department of Civil and En- vironmental Engineering, Utah State Univer- sity, Logan, Utah 84322-4110. 1978; Trihey 1979; Glova 1982). The process includes the development of stream hy- draulic models, stream temperature models, simulation models of physical stream hab- itat (Milhous 1979; Milhous et al. 1981), and biological models or criteria for fish microhabitat preference known as habitat suitability index (SI) curves (Bovee 1982; Rivers • Volume 1, Number 1 Pages 31-42 31 '?