8178

• UCREFRP Catalog Number: 8178
• Author: Anderson, R. and G. Stewart.
• Title: Riverine Fish Flow Investigations.
• USFW Year: 1999.
• USFW - Doc Type: Fort Collins, CO.
• Copyright Material: NO

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Prewitt (1977) found white sucker and their hybrids (white x flannel mouth and
white x bluehead) comprised a small proportion of suckers collected (1%) at Lily Park,
but were 19% of the suckers at Maybell and 76% at Craig in samples taken in 1975 and
1976. Current white sucker composition at Sevens and Duffy appear to be similar to
Prewitt (1977). In this study white sucker and white hybrids were 21% at Sevens and
87% at Duffy of the total sucker catch. Prewitt (1977) reported white hybrids were
about 50% of the WSWX group at Maybell and 23% at Craig. In this study white
hybrids were over 50% of the sucker catch in both areas.

Both early and recent surveys report white sucker were rare in the Lily Park area
and an increasing trend for white sucker in the upstream reaches. Since there appears to
be a consistent longitudinal trend for white sucker, it could be that elevation or
temperature is a regulating factor in the increased abundance at upstream sections.

The highest native fish composition in the Yampa River is in the Lily Park area.
This is due to white sucker being very rare and flannel mouth sucker abundant. The
distance between Lily Park and the Sevens is less than ten river miles and Lily Park is
only about 160 feet lower in elevation. A study site at Lily Park could add information
about white sucker distribution in upstream reaches. An effort will be made to
electrofish this area in September 1999 and to quantify habitat availability if time
permits.

. Several differences in density and biomass were noted between the
representative reaches, but differences between the two surveyed sites were less
dramatic. Both study sites had similar total fish density and biomass estimates, but there
were differences between individual species. Flannelmouth sucker and catfish were
more common at Sevens, while white sucker and white sucker hybrids were abundant at
Duffy .

The surveyed site included a single riffle-run sequence in both Sevens and Duffy.
It was determined that the riftle-run sequences selected for habitat analysis did not have
a fish community representative of the longer reach. The Sevens representative reach
had five riffle-run sequences of various lengths. At Duffy there were six riftle-run
sequences. The 1998 fish sampling effort focused on sampling one riffle-run sequence.
In the 1999 field season, fish in different riffle-run sequences will be uniquely marked.
This will allow for a more detailed examination of the relationship between habitat and
fish distribution and abundance

INVERTEBRATES

The intent of the invertebrate samples was to examine for a relationship between
wettedriftle area and invertebrate abundance. One result was that shallow portions of
the riffle sampled in September 3 dried for a period of about 10 days and then
reinundated about 20 days prior to sampling on October 8. This indicates that
recolonization of reinundated portions of these riffles would require more time than
observed. However since mean density was similar at Duffy for September and
October a reduction in flows during that' period did not appear to impact total density.