8105

• UCREFRP Catalog Number: 8105
• Author: Haines, G. B., D. W. Beyers and T. Modde.
• Title: Estimation of Winter Survival, Movement and Dispersal of Young Colorado Squawfish in the Green River, Utah.
• USFW Year: 1998.
• USFW - Doc Type: Recovery Program Project 36,
• Copyright Material: NO

Colorado squawfish were captured on 7-10 August 1995 (23 backwaters sampled with 82 seine
hauls). In the Canyonlands reach, 25 age-1 fish were captured on 1-4 August 1995
(60 backwaters sampled with 163 seine hauls). One fish marked during autumn was recaptured
on 2 August 1995 approximately 10-km downstream of the section where it was originally
captured.

Population and Survival Estimates
Fish capture and marking. - A total of3,779 young Colorado squawfish were captured;
2,478 were marked and released; and 188 were recaptured (Appendix la-e). All backwaters were
seined in each study reach. The number of backwater and low-velocity habitats seined per
sampling pass ranged from 9 to 33 (mean = 19.9) for the Jensen reach and 17 to 52 (mean = 36.6)
for the Canyonlands reach. The numbers of backwaters varied from year to year because of
variations in discharge and the geomorphology processes that form backwaters; numbers varied
from pass to pass primarily because small variations in discharge dewatered some habitats and
flooded others. In most cases, however, the largest and deepest backwaters, where most of the
young Colorado squawfish were captured, persisted from pass to pass. The Jensen reach had
cooler water temperatures and more inclement weather during sampling compared to the
Canyonlands reach. The number of days required to complete a three-pass population estimate
ranged from 6 to 33 d for the Jensen reach and 6 d for the Canyonlands reach.
Survival of marked fish held overnight in enclosures averaged 85% (Table 2). The
enclosures themselves were the source of some mortality. On one occasion small fish were
entangled in the mesh of the enclosure, and on another it was suspected that sediment deposition
and abrasion caused by wind turbulence may have resulted in mortalities.
Juvenile fish ranging from 100 to 230-mm TL were also caught in seine samples. In the
Jensen reach, four juveniles were caught in 1994; none were caught in 1995. Ninety-six
juveniles were captured in the Canyonlands reach in 1995 and three in 1996.
Size. - Length-frequency histograms for young Colorado squawfish showed that size in
autumn varied yearly (Figures 3-6). Growth of age-O fish at the Canyonlands site in

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