8182

• UCREFRP Catalog Number: 8182
• Author: Bestgen, K. R. and L. W. Crist.
• Title: Response of the Green River Fish Community to Construction and Re-regulation of Flaming Gorge Dam. 1962-1996\
• USFW Year: 2000.
• Copyright Material: NO

fish were measured (total [TL] and standard [SL] lengths) and sex and reproductive condition of
specimens was noted. Large samples of small-bodied fish captured by electrofishing were
simply counted. In addition, rare fishes were individually weighed and scanned for the presence
of a PIT tag. If none was detected, a PIT tag was implanted into the body cavity via a heavy bore
syringe, and the fish was released. Special care was taken to identify potential catostomid
hybrids. We identified these based on morphological characteristics of the mouth and body that
were intermediate between putative parental types and on intermediacy of scalation patterns and
scale counts in the lateral series (Hubbs and Miller 1953). Vouchers of some specimens,
including catostomid hybrids, were preserved in 10 % formalin, and are housed at the Larval
Fish Laboratory, Colorado State University.
Temporal and spatial changes in fish community composition.-Changes in fish
community composition over time were assessed at several levels of resolution and spatial scale.
We compared composition and reproductive status of fishes in the regulated reach for time
periods corresponding to just prior to closure of Flaming Gorge Dam (historical), just after
reservoir filling and commencement of normal operations that began in 1967, after penstock
modifications in 1978, and after discharge re-regulation in 1992 (this study). Data were gathered
from historical sources (Gaufin et al. 1960, Banks 1964, Smith 1966, Vanicek et al. 1970,
Holden and Crist 1981); assessments of reproductive status were made using presence of young
fish or by assumptions about the probability of such given water temperature regimes in the
reach. Reproductive status of fishes from 1967-1978 was inferred from data gathered in 1964
and 1966 by Vanicek et al. (1970) and data collected in 1978 (Holden and Crist 1981) prior to
temperature modifications. Data describing the reproductive status of fishes in 1965 were not
used because flows from Flaming Gorge Dam were low and warm in those years and not typical
of conditions from 1967-1978 (Vanicek et al. 1970).
Changes in species composition and relative abundance of fishes in Lodore Canyon were
assessed by comparing fish species composition information collected in the period 1978-1980
(Holden and Crist 1981) to that collected during -1994-1996. Holden and Crist (1981) sampled