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

A main challenge of testing river restoration hypotheses is linking population
measurements such as fish abundance to a driving variable or set of variables with reasonable
certainty. For example, it is difficult to isolate effects of flow or temperature regimes when
distribution and abundance of invasive species are expanding, perhaps though interactions with
variable environmental conditions (Bestgen et al. In press). Because cause and effect
experiments are not possible in this setting, correlations and weight of evidence approaches are
the prevailing technique to accomplish this (Beyers 1998). Populations that are composed of
species whose biology is poorly understood and which are relatively long-lived make these
assessments more difficult, because responses to changes are slow and assignment of causative
factors is difficult.
The reach of the Green River, Utah and Colorado, downstream of Flaming Gorge Dam
offers an opportunity to evaluate effectiveness of actions to re-establish native fishes. This is an
ideal study area because more natural hydrologic and temperature regimes designed to benefit
native fishes have been implemented over a series of years. The Green River also has a source
pool of native fishes downstream, including the mostly unregulated and tributary Yampa River
and regulation-attenuated downstream reaches of the Green River, to re-colonize upstream
reaches. Furthermore, descriptions of the fish community are available from immediate pre-dam
(pre-1962) and post-dam (1964-1966) periods, as well as before and after installation of a
temperature control device (1978-1980). Additional sampling was conducted from 1994 to 1996
that further evaluated changes in the fish community following implementation of flow
recommendations contained in the 1992 Biological Opinion on operation of Flaming Gorge Dam
(U. S. Fish and Wildlife Service 1992, Bestgen and Crist 2000).
Since 1996, a new set of flow and temperature recommendations for the Green River was
developed (Muth et al. 2000). Those recommendations will not be fully implemented until
Endangered Species Act and National Environmental Policy Act compliance activities are
complete, which is expected in 2006. Annual peak and base flow recommendations were
developed for each of five hydrologic conditions that ranged from dry to wet, based on
exceedance probabilities: dry (90 to 100% exceedance), moderately dry (70 to 90% exceedance),
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