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

declined 81, 83, and 85%, respectively, between the periods. Mountain whitefish was the only
native fish to increase in abundance between the periods and that difference was slight.
Size structure changes for native fish in Lodore Canyon showed that small individuals
(300 mm TL or less) were less common in 2002 to 2004 compared to 1994 to 1996, which may
reflect diminished recruitment for those species. Reduced recruitment may also partially explain
lower abundance of adults in 2002 to 2004 period. Differences in roundtail chub length
frequency in the Green River upstream of the Yampa River (all large) and downstream (mixed
sizes) may reflect differences in the predator fish community in each reach; this is discussed
below in more detail.
Reduced absolute abundance of native fishes and lower recruitment in Lodore Canyon
and elsewhere may be a function of increased abundance of non-native fishes. For example,
increased abundance of red shiner may cause increased levels of predation on early life stages of
all native fishes, including catostomids (Ruppert et al. 1993, Bestgen et al. 1997, Bestgen et al. in
press). Fathead minnow is also an efficient predator on catostomid fish larvae, and their
increased abundance may be associated with reduced survival of early life stages of native fishes
(Dunsmoor 1993). Effects of small-bodied predators are likely most severe when age-1 and 2
fish prey on larvae of native fishes. Larger larvae, juveniles, and small-bodied adults of some
native fishes that may or may not occupy backwaters may be affected by other predators as well.
These include expanding populations of smallmouth bass and channel catfish in the study area,
particularly Lodore Canyon, and brown trout which remained abundant in Lodore Canyon in
2002 to 2004.
Non-native fishes.-All trouts were combined to illustrate the general abundance pattern
for salmonids (excluding whitefish) because those cold-water taxa responded similarly to
environmental conditions. Brown trout constituted about 85% of all trouts captured, with
rainbow trout and rainbow x cutthroat trout hybrids (plus a few cutthroat trout, Snake River
subspecies) constituting the other 15%. Brown trout was found in all study reaches except
Island-Rainbow Park. In both time periods, salmonid abundance patterns were similar: they
were most common in upper Lodore Canyon (LD2) and were abundant (Fig. 24); CPUE for the
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