7752

• UCREFRP Catalog Number: 7752
• Author: Stanford, J. A.
• Title: Instream Flows to Assist the Recovery of Endangered Fishes of the Upper Colorado River Basin
• USFW Year: 1993.
• USFW - Doc Type: Review and Synthesis of Ecological Information, Issues, Methods and Rationale.
• Copyright Material: NO

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of the potamon zone has decreased as a consequence of the downstream extension (discontinuity)
of the rhithron zone through regulation of flow from the deep storage reservoirs. The concept of
ecosystem "resets" and discontinuities (sensu Ward and Stanford 1983), coupled with the notion
that connected channel and floodplain (backwaters, wetlands) components of the riverscape are
seasonally pulsed by flooding (Ward 1989), robustly integrate the myriad of biophysical processes
that are influenced by stream regulation. Strong inferences about how a river ecosystem may
respond to alternative flow management actions must be derived in this ecosystem context. The
downstream shift in the position of the rhithron-potanlon transition is an ecosystem-level measure
of change wrought by regulation and should be used as to adjust flows to maximize conditions
known to be favorable to both potamon (e.g., endangered fishes) and rhithron (e.g., trout) fisheries.
7) Strong food web interactions are likely occurring as a consequence of the presence of a
wide variety of nonnative fishes, which now dominate fish communities throughout the Upper
Colorado River Basin. Despite obviously important effects of predation and competition for food
resources, very little written information exists about the ecology of nonnatives in the Upper
Colorado River Basin. High volume flows appear to reduce numbers of nonnative species, and
diversion dams installed many years ago (e.g., Redlands on the Gunnison River) may have
segregated nonnative populations and limited range expansion. However, much more information
is needed. I suspect that considerable unpublished data exists in files as a consequence of the
sampling effort required to collect significant numbers of the endangered fishes. If so, the
information should be examined relative what is known about the native species, and it should be
published. If not, sampling protocols should be developed to describe trends in nonnative
populations in all of the river segments. In addition, experiments (e.g., as described below in
Section VI) are needed to clarify interactions between natives and nonnatives.
8) River ecosystems are too complex to be described by simple detenninistic models or
constructs of individual attributes. Ecosystem components are N-dimensional, inherently variable
(stochastic) in time and space and interact in complex ways that cannot be predicted from simple,
logistic equations. Construction of an ecosystem model that describes all of the dynamic processes

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