8045

• UCREFRP Catalog Number: 8045
• Author: Pacey, C. A. and P. C. Marsh.
• Title: Resource Use by Native and Non-Native Fishes of the Lower Colorado River
• USFW Year: 1998.
• USFW - Doc Type: Literature Review, Summary, and Assessment of Relative Roles of Biotic and Abiotic Factors in Management of an Imperiled Indigenous Ichthyofauna-Final Report.
• Copyright Material: NO

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This report serves as a necessary step preliminary to implementation of a potentially
costly, long-term research program under auspices of RPA#4. Our objective was to
assemble a comprehensive database of information on native and non-native fishes,
their known habitat uses and preferences, and the potentials for interaction between
the two categories.
The fundamental question addressed was whether biotic or biologic factors exerted an
over-riding force in determining viability of native fish populations. It is suggested that
native fishes can successfully complete their life cycles in virtually any habitat as long
as that habitat is devoid of non-native species. It is further suggested that native fishes
cannot complete their life cycles in systems occupied by established populations of
non-native fishes, regardless of the nature of the shared habitat. Our approach to
address these questions was to critically examine available literature and attempt to
reach a conclusion as to the probability of success of a lower Colorado River habitat-
management program that would enhance native fishes by reducing conflicts with non-
native species. Because simple maintenance of native fishes has become a
mechanical practice and now routine at a number of locations throughout the Colorado
River basin, we herein define as successful only that habitat management which allows
native fish species to complete successive life cycle iterations, attain, and maintain
stable population structures (abundance, distribution of age classes, and sex ratio)
characterized by normal population dynamics (i.e., rates and variation in recruitment,
growth, and mortality), without human intervention.
PROBLEM STATEMENT
Can lower Colorado River habitat be managed in ways that enable native and non-
native fishes to co-exist, or do interactions between native and non-native species
preclude such co-existence independent of habitat? If the former is answered
affirmatively, what specific habitat management can be recommended to achieve co-
existence between native and non-native fishes?