8173

• UCREFRP Catalog Number: 8173
• Author: Gido, K. B. and D. L. Propst.
• Title: Habitat Use and Association of Native and Nonnative Fish in the San Juan River, New Mexico and Utah.
• USFW Year: n.d.
• USFW - Doc Type: \
• Copyright Material: NO

preliminary step towards assessing the complex role of

competition In fish assemblages composed of native and nonnative

fish specles.

Because mortality and displacement by disturbance events can

moderate abundance of fish species, resource availability is not

believed to be a limiting factor in streams that are

hydrologically variable (Baltz and Moyle 1993; Moyle and Baltz

1985; Grossman et al. 1985). Variation in habitat availability

and species abundances, however, may cause shifts in. habitat use

by individual species (Angermeier 1987; Baltz and Moyle 1993) .

Apparent competitive exclusion of native fish by nonnative fishes

has also been reported (Fausch and White 1981; Baltz et al. 1982;

Douglas et al. 1994). The timing and magnitude of the

disturbance regime appears to influence the importance of biotic

interactions in streams (Minckley and Meffe 1987). In San Juan

River secondary channels, where numerical abundance of nonnative

species exceeds that of native species (Gido and Propst, unpubl.

data) and hydrologic variability has been reduced by flow

regulation, there is presumably a higher potential for negative

interactions.

The research reported herein was part of a long-term,

multidisiplinary study to evaluate the responses of native and

nonnative fishes to biotic and abiotic changes in the San Juan

River that were, in part, induced by "experimental" reservoir

releases that mimic natural flow regimes. Our objectives were tc

1) describe habitat use by native and nonnative fish species in

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