9532

• UCREFRP Catalog Number: 9532
• Author: Anderson, R. and G. Stewart.
• Title: Riverine Fish Flow Investigations.
• USFW Year: 2000.
• USFW - Doc Type: Fort Collins.
• Copyright Material: NO

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DISCUSSION

Species composition, density and size structure for fish over .IS cm were very similar

between years on theYampa River. This indicates stable and consistent population

parameters at both Sevens and Duffy between 1998 and 1999. Significant differences in

species composition, density, and size were found between Duffy and Sevens in both years,

1998 and 1999. The differences identified between the two Yampa sites could be related to'

biological interactions, differences in macro habitat availability (temperature, water quality) or

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differences in meso-habitat availability (gradient, substrate particle size, riffle/run ratios).

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A lack offish under 30 cm, higher mean lengths for virtually all species, and a much

lower density estimate of only 410 fish/km at the Duffy site could suggest increased predatory

pressures there compared to the Sevens site. Duffy had the higher densit~ of large predator

fish, northern pike, smaUmouth bass and Colorado pikeminnow. Unfortunately it is not

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possible to compare habitat availability between the Sevens and Duffy sites at this time.

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Channel catfish catch abundance was similar between both Yampa stations and the 15- Mile

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Reach.

There were large differences found in habitat composition between Duffy and the 15-

Mile reach. At Duffy the dominant habitat type was shallow runs at 49% and that habitat was

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observed to be mostly unproductive in regards to adult fish. Shallow runs were only 5% of

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the habitat in the IS-mile reach. Another habitat type that is unproductive for adult fish is the

wetted-sand pool or low velocity areas with depths less than 0.2 m. This habitat was 11% at

Duffy at a flow of 600 cfs.

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The dominant habitat type in the IS-mile reach was riffles over O.Sm in depth. Areas

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of deep fast current comprised 64% of the surface area in the IS-mile reach study site. It is

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believed that the high amount of deep and fast habitat accounts for the high percentage (38%)
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