9556

• UCREFRP Catalog Number: 9556
• Author: Bestgen, K. R., K. A. Zelasko and C. T. Wilcox.
• Title: Non-native fish removal in the Green River, Lodore and Whirlpool canyons, 2002-2006, and fish community response to altered flow and temperature regimes, and non-native fish expansion.
• USFW Year: 2007.
• USFW - Doc Type: 115,
• Copyright Material: NO

transport may be particularly high from canyon reaches, because few shallow, channel margin
backwaters occurred where fish could find refuge.
In 2002-2004, trammel net samples yielded six native and eight non-native species, and
three hybrids, and captured the highest proportion of native fish (about 2/3) of any sampling gear
(Table 8). In 2005-2006, trammel net samples yielded five native and six non-native species,
and one hybrid and percent native fishes declined to about 50%. The overwhelming majority of
non-native fish captured during both time periods was channel catfish, which showed a large
increase in 2005-2006 (47%) compared to 2002-2004 (28%). The most common native fishes
captured in trammel nets in 2002-2004 were flannelmouth sucker and roundtail chub, but chub
abundance (relative and absolute) declined dramatically from 24% of captures in 2002-2004, to
12.7% in 2005-2006.
Drift net sampling.-Drift net sampling was also conducted in 1994 and 1995 (Bestgen
and Crist 2000). Few fish species and individuals were captured in drift net samples in 1994 to
1995, diversity and number of fish captured increased substantially in the period 2002 to 2004,
and then number of fish captured declined again in 2005 and 2006 (Table 9 this report, and Fig.
43 in Bestgen et al. 2006). In 1994 to 1995, six species were captured and > 90% of those
individuals were native. Up to 16 species were captured in a single year (2003) in the 2002 to
2004 period, when substantially more non-native taxa were captured than in previous years (33%
native fishes captured). Fewer taxa and individuals were captured in 2005 and 2006, but native
fish increased to 46% of the sample. Notably, two Colorado pikeminnow larvae were captured
in summer 2006, and one likely early life stage razorback sucker (Bestgen et al. 2006 annual
report, project reports 115 and 22f).
Based on spawning ecology of Colorado pikeminnow and water temperatures that were
present in the Green River in Lodore Canyon, pikeminnow should have been able to spawn there
in all years of this study (Nesler et al. 1988, Bestgen et al. 1998). We are not sure why spawning
was not detected in other years, but the presence of ripe fish suggested that perhaps we did not
detect it if spawning occurred.
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