7157

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

22

The StJuthlllestem Naturalist

vol. :!!J. no. I

(Wick el al., 1981). Vanicek and Kramer (1969) collected larval and juvenile
squawfish in the Green River below its confluence with the Yampa. Tyus et
al. (1981), utilizing radiotelemetry techniques, observed an apparent spawn-
ing aggregation of squawfish in the lower Yampa consisting of individuals
which had migrated from the Green River in Utah and the upper reaches of
the Yampa. However, they cautioned that the presence of larval forms is the
best evidence of successful reproduction in a given area. The objective of
this investigation was to determine the distribution of larval (young-of-the-
year) squawfish in Colorado and to relate their occurrence to the hydrologi-
cal regime.

STUDY AREA.- The upper Colorado River basin, including those portions in Colorado, has
been the subjecl of numerous reports and publications because of Ihe focus on water development
and endangered species. Hydrology, geology, water-quality, and land-use were discussed tho-
roughly by Anonymous (1975). Hirsch et aI., (1977), Behnke and Benson (1980), Cushman et al.
(1980). and Wentz and Steele (1980). Our collections were made in selected reaches of the
C..olorado, Gunnison. White, and Yampa rivers where adult squawfish had been reported by
Everhart and May (1973), Holden and Stalnaker (1975), Seethaler (1978), Wiltzius (1978). Carlson
et al. (1979), Wick et al. (1981), and Tyus et al. (1982) and included sites in the vicinity of the
mosl upriver extent of the documented adult ranges (Fig. I). It was not possible to sample these
extensive areas entirely; however, sections of each reach were sampled thoroughly.
Collection localities were identified to the nearest 0.1 river kilometer. Kilometers on the upper
Colorado River are numbered upriver from km 0 at Lee's Ferry, Arizona to the Green River
confluence (San Juan County, Ulah) then up both the Green and Colorado rivers beginning with
another km O. The While and Yampa rivers are numbered upriver from km 0 al their confluence
with the Green in Uintah County, Utah and Moffat County, Colorado, respectively. The
Gunnison River is numbered upriver from its confluence with the mainsteam Colorado River
near Grand Junction (Mesa County, Colorado).
The main stem Colorado River study area extended for approximately 88 km from Palisades in
northcentral Mesa County to the Colorado-Utah boundary in western Mesa County (km 300.9-
212.5). The Gunnison River was sampled along an approximately 26 km reach from the vicinity
of Dominguez in western Delta County to Whitewater in central Mesa County (km 67.5-43.4) and
al a lower section near its confluence with the Colorado River al Grand Junction (Mesa County)
(km 4.8-2.6). The White River study area extended along an approximately 72 km reach from Rio
Blanco Lake in central Rio Blanco County to Rangely in western Rio Blanco County (km 243-
170.5). The YampaRiver was sampled along an approximately 195 km reach from the
Roundbollom area immediately west of Craig in eastern Moffal County to its confluence with the
Green River in Dinosaur National Monument in western Moffat County (km 194.8-0). This
section included three specific canyon areas in which there was a noticeable increase in gradient,
i.e., Juniper Canyon (km 146.4-145.7), Cross Mountain Canyon (km 94.6-89.6), and Yampa
Canyon in Dinosaur National Monument (km 72.4-0).

METHODs.-Collections were made during and after those time periods in which other
researchers (Vanicek and Kramer, 1969; Holden and Stalnaker, 1975; Seethaler, 1978; Wick et aI.,
1981) had suggested that squawfish spawn. Collections in the Colorado, Gunnison, and White
rivers were made during July-November 1979-81. Collections in the Yampa River were made
during July-October, <1980-1981. Collections were made during 4.5 day field trips utilizing rafts,
canoes and, in the Colorado, a power boat. Cross Mountain Canyon was surveyed entirely on foot
since the extremely turbulent nature of the canyon made float trips unsafe. Fishes were collected
with 3.0 X 1.2 m and 1.0 X 1.2 m seines (1.6 mm square mesh) and dip nets (0.79 mm square
mesh). Samples were collected according to the "qualitative representative sample" approach
(Hocull el aI., 1974) i.e. all available habitats that could be seined were sampled to obtain a
representative collection of species at a given locality. Current velocity was measured with a
Pygmy-Gurley current meter or with float techniques (Welch, 1948). Water temperature was
measured with a Taylor thermometer. Suspected squawfish larvae were preserved in 10% formalin
and returned to the laboratory for identification. Sampling effort was determined by availability