7332

• UCREFRP Catalog Number: 7332
• Author: Valdez, R. A., et al.
• Title: Final Report Habitat Suitability Index Curves for Endangered Fishes of the Upper Colorado River Basin.
• USFW Year: 1987.
• USFW - Doc Type: \
• Copyright Material: NO

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INTRODUCTION

BACKGROUND

The Fish and Wildlife Service (FWS) is using the Instream Flow Incremental
Methodology (IFIM) as a tool for evaluating the habi tat requi rements of the
endangered fishes of the Upper Colorado River Basin (UCRB). IFIM is a modular
system designed to simulate habitat as a function of streamflow (Bovee 1982;
Milhous et al. 1984). Habitat Suitability Index (HSI) curves, which are an
integral component of IFIM, are graphic representations of relative preferences
or tolerances for variables (depth, velocity, substrate, cover, and temper-
ature) that are important to the well-being of a species. Several techniques
are available for developing HSI curves (Bovee 1986); the method utilized often
depends on the quantity and quality of data available.

Data have bee~ collected for several years to determine the habitat needs
of the Colorado squawfish (Ptychocheilus lucius), humpback chub (Gila cypha),
and razorback sucker (Xyrauchen texanus) in the UCRB. Data from 1979-1984 were
used by FWS to develop HSlcurves in 1984 (U.S. Fish and wildlife Service
1984). There was some concern, however, that earlier data and data from other
agencies and organizations were not included in the analysis (on],y FWS data
were used), and that development of the curves was not well documented (Valdez
1985a) . Also, there was not general agreement concerning data analysis and
curve development techniques used by FWS in the 1984 exercise.

The purpose of this HSI CUrve Development Project was to assimilate all of
the data available from UCRB studies for the three target fishes, including
data collected by FWS as well as by State and Federal agencies and private
groups, and develop HSI curves that represent habitat used by these endangered
fishes. The project was designed to integrate and analyze all data; develop
HSI curves for all variables, life stages, and species; identify data gaps and
needs; and to evaluate the data and reach agreement by species experts on the
best possible curve sets, given the present knowledge. A consensus by species
experts was required to determine which data were suitable for analysis, how
curves were to be developed, and when and where these curves are applicable.

PROJECT OBJECTIVES

The goal of this project was to generate the best possible HSI curves or
criteria for depth, velocity, substrate, cover, and temperature, using the
existing data and the professional judgement of species experts, for all life
stages of the Colorado squawfish, humpback chub, and razorback sucker. The
bony tail chub (Gila elegans) was excluded from this analysis because of
insufficient information on the habitat and life history of this species. To
accomplish this goal, the following objectives were met:

1. Based on judgement of experts, determine which data within the
computerized database are suitable for quantitative analysis and use
in HSI curve development, versus those which are only useful for
substantiating use of certain habitat variables and types.

1