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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At Sevens, sand shiners were the dominant species in 1999 collected in seine hauls and
were also the most common species in 2001 (Table 5). Clearly sand shiners are the most
common fish in this section of the Yampa River and these fish are associated with habitat that is
not very common at Lily Park just 15 km downstream. The shift in species composition between
1999 and 2001 was not as dramatic at the Sevens, when compared to Duffy. There were much
fewer white suckers collected in 2001 (n=88, 4%) than in 1999 (n=588, 27%) (Table 5).
Smallmouth bass increased very slightly between 1999 (n=9, 0.4%) and 2001 (n=30, 1.5%).
However histogram data shows juvenile small mouth bass increased in 2001, and this could
explain the fewer white sucker YOY seined at Sevens in 2001.

Table 5. Species composition from seine hauls at the Sevens and Duffy sites in 1999 and 2001,
Yampa River.

STATION SEVENS SEVENS DUFFY DUFFY
YEAR 1999 2001 1999 2001
TOTAL (n) 2165 2026 2272 803
% (n) % (n) % (n) % n)
Flannelmouth sucker 1.1 (23) 5.4 (109) 1.0 (23) 0
Roundtail Chub 1.4 (34 2.2 (45) 34 733) 1.4 (11 )
Speckled Dace 3.8 (83 1.9 (39) 241 538) 0
Sand Shiner 57 (1241-' 82(1662) 13.9 (315) 29.5 (237)
White Sucker, &crosses 27 (588) 4.3 (88) 21.9 (497) 1.2 (11)
Small mouth bass 0.4 (9) 1.5 (30) 2.5 (57) 67 (5401
Fathead minnow 3.6 (77 2.5 (50) 0.4 (10 0.1 1
Carp 4.3 (93 0 1.5 (35 0.2 2
Stickleback 0.7 (16 0.1 (3 ) 0.4 (9) o c~..
Redside shiner 0.05 (1) 0 0.04 (1) 0
Plains Killifish 0.05 (1) 0 0 0

Yampa - Species composition discussion

Species composition for fish over 15 cm was strongly consistent at both Sevens and
Duffy over the first three years, but consistency was not maintained in 2001 (Tables AI). A
stable species composition indicates stability in habitat availability or biological factors
(competition or predation) that regulate population dynamics. Intrinsically it is understood there
is a relationship between habitat availability and species composition and abundance. If habitat
availability changes, then a concomitant change in the fishery is expected. An objective of this
study is to quantify habitat availability of these sites and determine the strength of the
relationship between habitat composition and fish composition by sampling site with different
habitats. The minor shift at Sevens and the major shift at Duffy in species composition in 2001
compared to earlier years suggest environmental changes that have been advantageous to
small mouth bass at Duffy. This environmental change is the extreme low flow conditions of
2000, exacerbated by another very low flow year in 2001.

The discrepancy in species composition and more specifically for small mouth bass
between Duffy and Sevens strongly suggests local channel morphology or habitat availability is

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