9556 - Laserfiche WebLink

Home Browse Search

canyons as a result of construction and operation of Flaming Gorge Dam. We characterized flow differences in the historical period (Lodore Canyon, Greendale gauge, # 09234500, RK 660, 1951 to 1962; Whirlpool Canyon, Jensen gauge # 09261000, RK 486.2, 1946 to 1962), apost- impoundment period (1962 to 1991), apost-Biological Opinion period (1992-1996), and a recent (1997 to 2006) period which was thought to represent conditions that affected the fish communities during this investigation. We used the gauge near Jensen, Utah, to characterize Whirlpool Canyon and Island-Rainbow Park flows because the few small tributaries present between Whirlpool Canyon and the downstream gauge will not affect flow estimates appreciably. Fish sample data analysis and presentation.-Composition of the fish community in the study area (Fig. 1) was calculated for samples collected in the 2002 to 2004 period for each gear type, and also for the 2005 to 2006 period. We grouped samples in this manner because 2002- 2004 data were reported previously (Bestgen et al. 2006), and it made sense to compare those findings with more recent data collected in 200.5 and 2006. Longitudinal and temporal shifts in community composition were characterized by partitioning samples into reaches for large-bodied fishes captured primarily by electrofishing in the periods 1994 to 1996, 2002 to 2004, and 2005 and 2006. Seine sampling data was used to supplement observations gathered for large-bodied fishes, but that data is not extensively featured here. In some cases, we cite the recent and extensive analyses in Bestgen et al. (2006) rather than duplicate those results here. Samples were from eight contiguous Green River reaches: a Browns Park reach, four 8-RK Lodore Canyon reaches, upper and lower Whirlpool Canyon reaches (9 and 8 RK) and the Island- Rainbow Park reach (10 RK); electrofishing was conducted only in Lodore and Whirlpool canyons. Change in numerically dominant native and non-native fishes in reaches was compared among study periods 1994 to 1996, 2002 to 2004, and 2005 and 2006, and reaches to facilitate detection of longitudinal shifts in community composition. We defined relative abundance as the percent composition that a particular species represented in a sample. For electrofishing samples, CPUE was number of fish captured per amount of time sampled. In general, relative 13