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

abundance of natural populations. A first challenge is obtaining reliable measurements of the
population parameters of interest so that inferences can be made with confidence. We think we
did a reasonable assessment of the fish community because our sampling was spatially and
temporally intensive and we used a variety of gears to sample nearly all life stages of fish present
in the system. Linking population measurements such as abundance levels to a driving variable
or set of variables with certainty is another major challenge.
These difficulties not withstanding, we believe reasons for some observed changes in the
fish community in the period 2002 to 2004, as compared to previous periods, were associated
with changes in flow and temperature regimes. Expanded distribution and abundance of red
shiner, sand shiner, channel catfish, and smallmouth bass were almost certainly a product of low
flows and, particularly, warm temperatures. Water temperature in mid-summer in Browns Park
and upper Lodore Canyon may be 2 to 3°C cooler than in lower Lodore Canyon (Bestgen and
Crist 2000). However, upstream observations of 22°C or more were recorded in our study,
conditions which likely promoted upstream expansion by warm water species. Distribution and
abundance of most other non-native fishes also increased.
Warmer summer base flows may also have benefitted Colorado pikeminnow. Although
our electrofishing data from 2002 to 2004 indicated a slight decline in Colorado pikeminnow,
Kitcheyan and Montagne (2006) detected large numbers of Colorado pikeminnow in Lodore
Canyon in 2002 and 2003, when flows were low in the rest of the basin. We did not detect
reproduction based on capture of larvae in drift nets, but we collected ripe Colorado pikeminnow
in Lodore Canyon in 2003 and there was a similar report in 2001 (T. Modde, pers comm., U. S.
Fish and Wildlife Service, Vernal, Utah). Further, Kitcheyan and Montagne (2006) also reported
small aggregations of Colorado pikeminnow during summer at two locations in Lodore Canyon,
which may represent spawning groups. These data support the contention that lower and warmer
summer base flows in Lodore Canyon may be a benefit to Colorado pikeminnow.
We did not anticipate reduced abundance of most other native fish of all life stages in the
study area during 2002 to 2004. Declines in relative abundance of young native fishes may be a
function of the influx of large numbers of non-native cyprinids that were captured in seine
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