9555

• UCREFRP Catalog Number: 9555
• Author: Bestgen, K. R., C. D. Walford, A. A. Hill and J. A. Hawkins.
• Title: Native Fish Response to Removal of Non-native Predator Fish in the Yampa River, Colorado.
• USFW Year: 2007.
• USFW - Doc Type: 140,
• Copyright Material: NO

relatively abundant and thus, not likely to be missed in sampling efforts, it likely represents a
new introduction or invasion from upstream.
Yampa River.fishes, relative abundance.-Relative abundance (% composition of a
species in a sample) of species in the fish community in the study area also appears to have
changed between the 1981-1982 period and our study, 2003-2006. Native species comprised
about 27% of samples collected in 1981-1982 (23-32%, Wick et al. 1985) compared to 3.8%
(1.3-9.2%) in 2003-2006 (Table 4). Roundtail chub were the most abundant native species
present in each period.
Relative abundance of native fishes during this study was highest in 2004, when relative
abundance of smallmouth bass (19.3%) was the lowest observed in the 2003-2006 period. This
may also be related to the relatively high proportion of isolated pools sampled in 2004, relative
to other years, where bass are less abundant.
Data from Anderson (2002, his Table 5) suggested that declines in small-bodied native
fish abundance occurred relatively recently, based on seines samples collected in our study area.
As recently as 1999, flannelmouth sucker (1%, n = 23 individuals), roundtail chub (34%, n =
733), and speckled dace (24%, n = 538) comprised 59% of the fish community (n = 2,272 fish
collected) in low-velocity nearshore habitat seine samples. In 2001 in the same study area (no
samples collected in 2000), no flannelmouth sucker or speckled dace were captured (n = 803 fish
collected), and only 11 roundtail chub were captured, for a total native fish relative abundance of
1.4%. White sucker relative abundance also decreased from 21.9% in 1999 to 1.2% in 2001.
The main shift in non-native species abundances from 1999 to 2001 appeared to be
related to smallmouth bass, which increased from 2.5% (n = 57) in 1999 to 67% (n = 540) in
2001 (Anderson 2002). Water temperatures in 1999 were relatively cool, but were warmer in
2000 and 2001. Anderson (2002) suggested that increased water temperatures may be related to
the large increase in age-0 smallmouth bass abundance in 2001, and continued warm water
temperatures in the drought period 2003-2006 may be contributing to continued high smallmouth
bass abundance in the study area. The increase in relative and absolute abundance of
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