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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DISCUSSION

FISH SAMPLES

Significant differences were identified in the fish community between Duffy and
Sevens for species composition, density and size structure. Native species composition
was higher, density was generally higher and mean size was generally lower for fish at
Sevens compared to 50 miles upstream at Duffy. Results of recent sampling (1994 to
1998) by the interagency standardized monitoring program (ISMP) were similar to this
study, finding native species composition highest at Lily Park and the lowest 50 miles
upstream at Morgan Gulch (Bill Elmblad, CDOW unpublished data 1995 - 1998).
However collections made in the 1970s and 1980s tend to indicate a larger native fish
population in the upstream reaches (Maybell, Juniper and Craig). Holden and Stalnaker
(1975) characterized flannel mouth and bluehead sucker abundant at all four locations
they sampled in the Yampa River, which include Juniper and Craig. Surveys by Miller
(1982), Carlson (1979), and Wick (1981 and 1986) report flannelmouth sucker
composition between 25 and 75% at Lily Park, 45 and 55% at Maybell, and between 34
and 64% near Juniper and Craig. The current percent composition of flannel mouth
sucker (6%) appears much less for Maybell and upstream than found earlier. It appears
highly unlikely that the reduced flannel mouth population upstream of May bell is related
to recent alterations in physical habitat.

Present composition of blue head sucker appears fairly similar to that reported by
Miller (1982), Carlson (1979), and Wick (1981 and 1986) for the Lily Park and Maybell.
However, these authors report bluehead composition between 7 and 39% for Juniper,
generally higher than found in 1998 at Duffy (4%) and with ISMP sampling at Juniper
(6%) (Elmblad pers. comin.). Bluehead sucker are generally found tobe associated with
riffle habitat and any changes in their composition over this time period were not
attributed to presumed changes in habitat or to flow alterations.

Composition of round tail chub reported by Miller (1982), Carlson (1979), and
Wick (1981 and 1986) averaged 9% for Lily Park, 8% at Maybell and 11% at Juniper.
Composition of round tail chub in this study (6% at Sevens and 3% at Duffy) appears to
be a less than earlier reported downstream of May bell and considerably less upstream of
Juniper. Adult roundtail chub are strongly associated with deep pool habitat, and pool
habitat availability likely has not changed significantly over the last twenty years.

It appears more likely that any recent changes in flannel mouth, bluehead sucker
and roundtail chub abundance upstream ofMaybell are more likely a consequence of
recent introduction of small mouth bass instead of habitat alteration. Small mouth bass
were first collected in the river in 1992 when Elkhead reservoir was drained (Nesler
1995). Nesler (1995) believed that small mouth bass were unlikely to become
established in the Yampa River due to lack of suitable habitat. Several hundred
small mouth bass YOY were collected at Duffy and bass reproduction has probably been
successful in most of Little Yampa Canyon. Smallmouth bass appeared to be strongly
associated with deep pools with cover provided by large boulders. This habitat was
common at Duffy but rare at Sevens.

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