9433

• UCREFRP Catalog Number: 9433
• Author: Anderson, R.
• Title: Riverine Fish Flow Investigations.
• USFW Year: 2002.
• USFW - Doc Type: Federal Aid Project F-288-R5,
• Copyright Material: NO

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flannelmouth sucker composition at Clifton in 2001 (42%) was somewhat higher than the prior
year. Factors that could explain these minor discrepancies in species composition include that it
could be there was a true shift in species composition or that it could be an artifact of sampling
efficiency between years. It is more likely that the variation noted for 2000 is a result of
sampling efficiency. Sampling efficiency can be influenced by flows, visibility of water, effort,
and ability ofnetters. Flow conditions during sampling was fairly similar in 2000 and 2001, but
flows were much higher 1999 (Figure 3). In 2000 sampling after thunderstorms or during
reduced water visibility was more common, and there were fewer passes made in 2000 than in
1999 and 2001. Also shoreline habitats received proportionally more effort in 2000. Therefore,
it is believed that differences between years for tlannelmouth and bluehead composition is less
than the data in Table 3 indicates.

Common carp was the most common nonnative species of fish over 15 cm collected at
both sites in 2001. Carp were 6% at the Com Lake site and 14% at Clifton (Table 6). In 1999
and 2000 carp comprised 11% and 14% of the catch, respectively so the 6% of 200 1 was much
lower than in the two prior years. At Clifton carp composition was 16% in 1999, 12% in 2000 so
the 14% in 2001 was very similar to prior years. The discrepancy in carp percentage at Com
Lake in 2001 (6%) could suggest more movement of carp during 2001.

White sucker plus white hybrids with flannel mouth and bluehead comprised 6.2% at
Com Lake in 2001 and 4.1 % at Clifton in 2001 (Table 6). These percentages are similar for
white sucker in Com Lake in 1999 and 2000 at 5.6% and 5.3%, respectively and at Clifton at 5.0
and 3.7% respectively. Also white sucker were more common in backwater habitats than in the
main channel. Channel catfish also had similar species composition between years with 4.7% in
2001, 6.3% in 2000 and 4.2% in 1999 at Com Lake. In Clifton, catfish composition was 5.7% in
2001 and 5.1 % in 2000.

Fish less than 15 em

Since speckled dace were very common and occupy swift habitats somewhat difficult to
sample, dace and mottled scuplin were not netted but counted by netters. Therefore, dace and
sculpin composition is not based on catch rates so their composition is not proportional to their
actual population size. However, these counts will be very useful for documenting their
distribution and habitat associations in the Colorado River. In contrast, all sunfish sighted were
netted, and most originated in backwater habitats. Sunfish removal was tried in 2001 and 2000,
but not in 1999, since the recovery program was conducting sunfish removal during this time.
Non-native cyprinds (NNC; red shiner, sand shiner and fathead minnows) were very abundant in
shoreline habitat and backwater habitats, but relatively few were netted. No effort was made to
quantify abundance or composition ofNNC since these fish are not going to be used to justify
flow recommendations and numerous other sources are available for data concerning this fish
group, Valdez (1999), Bestgen et al (1999) and McAda (IS:MP).

It is highly likely that the most common fish in the under 15-cm group for the IS-mile
Reach belong in the NNC group. The next most abundant species is highly likely to be speckled
dace, which had the highest composition as reported in 2001 at both sites (Table 6). YOYand
juvenile flannel mouth and bluehead sucker and roundtail chub were collected in all years

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