9522

• UCREFRP Catalog Number: 9522
• Author: U.S. Fish and Wildlife Service.
• Title: Life History of the Colorado Squawfish in the vicinity of Tusher Rapid.
• USFW Year: 1984.
• USFW - Doc Type: Vernal.
• Copyright Material: NO

INTRODUCTION
The Colorado River Fisheries Project, funded primarily by the
Bureau of Reclamation, initiated a monitoring program for evaluating the
life history requirements of Colorado squawfish (Ptychocheilus lucius),
and other endangered fishes in the Green River Basin in 1979 (Tyus et
al. 1982). That program, which is part of a more comprehensive study,
has been expanded and continued through the present (1984). This report
provides life history information for the various life stages and activities
of Colorado squawfish in the vicinity of Tusher Rapid, near the city
of Green River. Tusher Rapid is caused by alluviual material which
flows into the Green River from Tusher Wash,a seasonal watercourse
that enters the river at the Thayn Project site.
The genus Pt chocheilus includes the largest cyprinids in North
America. Represented by four species today, the ]argest of these, the
Colorado squawfish (Ptychocheilus lucius Girard) previously grew to a
size of about 1.8 m and 45 kg (Miller 1961). Endemic to the Colorado
River Basin this fish, once distributed throughout the basin has declined
since the 1930's and is today restricted to the upper Colorado River
Basin where it is classified as endangered by the U.S. Fish and Wildlife
Service (1973, ]974). The loss of the Colorado squawfish from parts of
the Colorado River is apparently related to major water developments
which have ostensibly reduced P. lucius to about 25~ of its former range
(Tyus 1984). Although many workers have postulated man-induced changes
in riverine conditions as primary factors in the reduction of the range
and abundance of this species (Miller 1961, Holden and Wick 1982,
Ono et al. 1983.), a lack of basic knowledge about life history