9549

• UCREFRP Catalog Number: 9549
• Author: Bestgen, K. R., K. A. Zelasko, R. I. Compton and T. Chart.
• Title: Response of the Green River Fish Community to Changes in Flow Temperature Regimes from Flaming Gorge Dam since 1996 based on sampling conducted from 2002 to 2004.
• USFW Year: 2006.
• USFW - Doc Type: 115,
• Copyright Material: NO

increased 243% between the two sampling periods. Currently, smallmouth bass and green
sunfish are more common in backwaters where few or none previously existed; their abundance
has increased by several orders of magnitude.
Increased hybrid sucker numbers in Lodore Canyon between 1994 to 1996 and 2002 to
2004 periods may be due in large part to relatively recent expansion of white suckers into the
Green River upstream of the Yampa River. A single specimen of that species was detected in a
rotenone sample taken in September 1957 in the Green River in Browns Park (Molting 1957).
White sucker was not detected in samples collected just after impoundment of Flaming Gorge
Reservoir and was rare in collections made by Holden and Crist (1981) in 1978 to 1980.
However, white sucker was relatively common from 1994 to 1996 and 2002 to 2004, particularly
in upstream Browns Park where water was colder. Razorback x flannelmouth sucker hybrids
were detected as long ago as 1889 in the Upper Colorado River Basin and in 1950 in the upper
Green River near Hideout Canyon (Hubbs and Miller 1953), so some level of hybridization of
native taxa should be expected even under relatively pristine conditions. However, the variety of
hybrid combinations and their abundance in the Green River appear to be recent phenomena, as
Holden and Crist (1981) reported only a few hybrids.
Some hybrid specimens appeared to have traits of white, bluehead, and flannelmouth
sucker, which may indicate some level of back-crossing among hybrids. The relatively high and
apparently increasing number of hybrids noted in this study and in other areas (Holden and
Stalnaker 1975a; 1975b), and the large number of hybrid combinations, suggest that this
phenomenon deserves further study. Detection of hybrids in field samples will be critical to
accurately determine the extent of hybridization and whether the proportion of hybrids among all
catostomids present is increasing over time. A better understanding of hybridization
mechanisms and hybrid fertility, especially in river reaches strongly affected by regulation, may
also aid restoration of rare catostomids such as razorback suckers.
Effects of season, year, and turbidity on capture success, electrofishing samples.-The
overall effect of season on the average catch rate of all fish species in samples from 1994 to 1996
was significant (xZ = 68.17, 2 df, p < 0.000 1), with catch rates higher in autumn (3.14 fish/h,
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