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From: i!)/OO8_ - IJ ~ ~~ /Jtu2 ("l'111 Edit~:;d b::{ {Plenurn J I ECOLOGY OF RIVERINE FISHES IN REGULATED STREAM SYSTEMS WITH EMPHASIS ON THE COLORADO RIVER Paul B. Holden BIO/WEST, Inc. P.O. Box 3226 Logan, UT 84321 INTRODUCTION Riverine fishes can be defined rather simply as species that inhabit rivers. This simplistic definition may suffice for general informational needs, but is insufficient when describing impacts. Some fishes that live in rivers require the river's environment for sustenance of their populations, e.g., Pacific salmon (Oncorhynchus spp.), paddlefish (Po~yodon spathu~a), and blue sucker (Cyc~eptus eZongatus). Other riverine species can do just as well, or better, in lakes, ponds, or other lentic environments, e.g., carp (Cyprinus carpio), fathead minnow (PimephaZes promeZas), and bass (Micropterus sp.). Therefore, changes in a natural river's flow, temperature, water quality, or physical morphometry may affect certain species more than others; more likely it will affect those species that require lotic conditions to a greater extent than those which also tolerate lentic conditions. " Riverine fishes include obligate and faculative riverine species. Obligate riverine fishes may be further subdivided into those requiring rivers for all their ecological needs, such as most darters (Etheostoma sp., Percina sp.) and the blue sucker, versus. . those that require rivers for only a portion of their life histQry,'~ such as salmon, paddlefish, and other migrating species. Fur:th'~';l'~".;_ subdivisions could be made but are not required for this d1s9\fsl:ii6j:f ...... t~-1 ' - :?P:3; --:'~- ",f--,-..~: .~'>f The initial intent of this paper was to concentrate on tWe" ,iA~Y' effects of dams on obligate riverine species, especially those that.?!," require natural rivers for all their ecological requirements. It soon became evident that this was not practical, because most of it 57