9432

• UCREFRP Catalog Number: 9432
• Author: Modde, T. and M. Fuller.
• Title: Feasibility of Channel Catfish Reduction in the Lower Yampa River.
• USFW Year: 2002.
• USFW - Doc Type: Vernal.
• Copyright Material: NO

declined in those reaches, however, Crowl and Badame (2000) also observed declining captures

later in the year, that did not correspond to declines observed in mark-recapture estimates, and they

attributed the reduced catch to changes in vulnerability to capture. The significant negative slope

of catch rates and significantly higher catch rates in the Yampa River control reaches indicated

that reduced catch rates in treatment reaches are not likely the result of changes in vulnerability.

Although it appears that channel catfish numbers were reduced in Yampa canyon, we feel it

unlikely that declines were as great as the 81 % suggested by regression analysis. It is probable

that angling effort was highly effective on fish smaller than 400 mm, however, angling effort

cannot be applied uniformly to all habitat types with every reach. In addition, fyke net and trot line

catches suggested that some larger fish were present in the river, but were not as vulnerable to

either angling or electrofishing. The density of channel catfish estimated in Yampa Canyon was

lower (88 - 180 fish/km) than reported in the San Juan River (between approximately 360 and 760

fish/km) by Brooks et al. (2000) , but similar to the estimates of Anderson (2000) in the Yampa

River above the study area (Sevens Ranch, rk 102, and Duffy, rk 177, reaches on the Yampa River

during 1999 were, 134/km, SEi: 192, and 11 O/km, SE i: I 08, respectively). Thus, it is reasonable

to conclude that removal efforts significantly reduced the. number of channel catfish in Yampa

Canyon, and was most effective in removing fish between 200 mm and 400 mm in total length.

The average length of fish removed varied by gear type. Most fish removed by angling

ranged between 200 mm and 400 mm. Fish captured from electro fishing tended to be smaller

individuals, and fyke and hoop net collections tended to capture larger individuals. However, the

majority of fish captured from all gear types ranged between 250 mIll and 400 mm, which Tyus

and Nikirk (1990) determined to be between approximately age-6 and age-12. The majority of

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