7157

• UCREFRP Catalog Number: 7157
• Author: Haynes, C. M., et al.
• Title: Larval Colorado Squawfish ‎(
• USFW Year: 1984
• Copyright Material: YES

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07157

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THE SoUTHWESTERN NATURALIST 29(1):21-33

MARCH 23, 1984

LARVAL COLORADO SQUAWFISH (PTYCHOCHIELUS
LUCIUS GIRARD) IN THE UPPER COLORADO
RIVER BASIN, COLORADO, 1979-1981

C. M. HAYNES, T.A. LYTLE, E. J. WICK, AND R. T. MUTH

ABSTRACT.-A survey of the Colorado River drainage in Colorado was made during the
summer-fall of 1979-1981 to determine the distribution of larval Colorado squawfish (Ptychochie-
Ius lucius) and to relate their occurrence to the hydrological regime. Squawfish larvae were
collected in the lowermost 31 km of the mainstem Colorado River in 1979-1981 and the
lowermost 29 km of the Yampa River in 1980-1981. Larval squawfish were not found in
collections from either the White or Gunnison rivers. Sampling effort appeared to have no effect
on collection success, but collection success did appear to reflect reproductive success and/or
larval survivorship. Estimates of spawning periods for the Colorado River range from as early as
18 June in 1981 to as late as 26 August in 1980. In the Yampa, we estimate that spawning
occurred as early as 16 June in 1980 and as late as 3 August in 1981. Our observations and
spawning period estimates support the hypothesis that reproductive success is related to both the
(Jow and temperature regimes; however, other exogenous (e.g. photoperiod, water quality, etc.)
and biotic factors (e.g. competition, predation) have yet to be adequately investigated.

The Colorado squawfish, Ptychochielus lucius, the largest native North
American cyprinid, is endemic to the Colorado River drainage. The species,
historically abundant and widespread from Wyoming to the Gulf of
California, has been functionally extirpated in the lower basin (below Lee's
Ferry, Arizona) and reproducing populations are restricted to the upper
basin (Minckley and Deacon, 1968; Holden and Stalnaker, 1975; Seethaler,
1978). Consequently, it is listed as endangered and subject to full protection
under the Endangered Species Act of 1973.
The decline of this apparently obligate riverine species has been attrib-
uted largely to physical habitat alteration resulting from the construction of
several large mainstream dams, beginning with Hoover Dam (1936) in the
lower basin and including Glen Canyon and Flaming Gorge dams in 1963
(Deacon et al., 1979; Holden, 1979; Behnke and Benson, 1980; Saiki et al.,
1980). Interaction with non-native species has also been suggested as a
factor in the delcine of the squawfish (Colorado River Fishes Recovery
Team, 1978; Behnke and Benson, 1980; Saiki et al., 1980).
In Colorado, squawfish are restricted to the lower and middle reaches of
the Colorado, Yampa, Gunnison, and White rivers and to that section of
the Green River near its confluence with the Yampa in Dinosaur National
Monument (Fig. 1) (Tyus et al., 1982), Mark-recapture techniques have been
employed in Colorado since 1979; however, because of low recapture
success, meaningful population estimates have not been possible (Wick et
al., 1981). Based on adult capture frequency, squawfish apparently reach
their greatest Colorado abundance in the mains tern Colorado and Yampa
rivers. Evidence of reproduction in Colorado prior to these collections has
been based largely on captures of ripe and/or spawned-out adults in the
Yampa (Holden and Stalnaker, 1975; Seethaler, 1978) and Colorado rivers