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

when temperature is suitable. Moreover, western rivers typically

have similar patterns of elevated flow in the spring as a result

of snow melt and infrequent flooding during late summer-autumn

(Poff and Ward 1989). Fewer disturbance events during late

summer-autumn may not suppress fish abundance below a level where

resources are not limiting.

Long-term monitoring is necessary to determine if negative

interactions or habitat shifts associated with interference

competition will gradually cause a decline or eventual

extirpation of common native species (e.g., R. osculus and ~.

latipinnis). Other native species in the San Juan River have

already experienced dramatic declines in abundance (e.g.,

Ptychocheilus lucius) that coincided with the impoundment of the

river and establishment of nonnative fish species (Platania et

ale 1991). Elsewhere in the Colorado River drainage, nonnative

species have been shown to be more aggressive (Karp and Tyus

1990) and competitively displace (Douglas et ale 1994) native

species. Overlap in habitat use observed in this study suggests

that if resources are limited, competition among native and

nonnative juveniles and larvae may negatively influence survival

and growth of native fishes. One scenario that would allow

species to coexist in this environment is that native species,

because they spawn early in the year, can attained larger body

size, and are thus better able to compete with the smaller

nonnatives for resources. Thus, a natural flow regime with

elevated flows during spring and early summer may be important to

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