6042

• UCREFRP Catalog Number: 6042
• Author: Haynes, C. M., R. T. Muth and T. P. Nesler.
• Title: Identification of Habitat Requirements and Limiting Factors For Colorado Squawfish and Humpback Chub.
• USFW Year: 1985.
• USFW - Doc Type: Fort Collins, Colorado.
• Copyright Material: NO

INTRODUCTION

As a consequence of declines in range and abundance, Colorado squawfish
(Ptychocheilus 1ucius) and humpback chub (Gila cypha) have been listed as
endangered by the federal government and the State of Colorado. Accordingly,
recovery plans have been approved for both species. Both plans recognize
several factors which appear responsible for the endangered status of these
Colorado River endemic species including habitat alterations (e.g., changes
in historical flow/temperature regimes); construction of in-channel
structures which are possible barriers to Colorado squawfish migrations;
introduction of non-native species with concomitant predation and/or
competition effects; and, in the case of humpback chub, hybridization with
congeners due to a presumed breakdown of reproductive isolating mechanisms.

Since 1977, the Colorado Division of Wildlife (CDOW) has been
investigating these species in Colorado via systematic sampling in portions
of the mainstem Colorado, Gunnison, White, and Yampa rivers. As a result of
this work and other studies (e.g., Vanicek 1967; Holden 1973; Seethaler
1978), considerable information has been gained regarding the overall
distribution of both species. Prior to 1981 however, limited information
existed relative to the reproductive range of either species, and knowledge
of their early life histories was sparse. The first documented captures of
larval Colorado squawfish in Colorado were from the mainstem Colorado River
west of Grand Junction (Mesa Co.) in 1979, and in the lower reaches of the
Yampa River (Dinosaur National Monument, Moffat Co.) in 1980.

This research project was initiated in 1981 as Federal Aid Project
SE-3-4. Due to the ongoing investigations of adult squawfish and humpback
chubs by the Colorado River Fisheri~s Project (CRFP, United States Fish and
Wildlife Service) and Nlv Region of CDOW, this study concentrated on the early
life history of these species within study areas where the occurrence of both
species had been previously documented. The objectives of this project were
to (1) delimit the reproductive range of Colorado squawfish in the lower
Colorado and Yampa rivers, Colorado, (2) evaluate factors limiting
reproduction and recruitment of Colorado squawfish, and (3) develop taxonomic
techniques for identifying and discriminating between early life history
stages of Gila species native to the Upper Colorado River Basin and their
hybrids. ----

During 1979-80, this project and its Principal Investigator, C. M.
Haynes, were associated with a similar project administrated by the NW Region
of CDOW. In order to provide a complete, up-to-date record of Colorado
squawfish early life history, data from those 2 years have been included in
this final report. Study Objective 3 will be addressed in a Ph.D.
dissertation (R.T. Muth, in preparation) which constitutes the humpback chub
portion of this final report.

Numerous other fish species were collected in conjunction with the target
species of this study. From length frequency analyses of the samples of
these other species, it was possible to construct observed and principle
spawning periods for each. This information was not germane to the
objectives of this study, but is included as supplementary data in Appendix
A. This data may prove useful in investigating the ecological interactions
of Colorado squawfish, humpback chubs, and other endangered fish species with
these other species.