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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correlated with diversity and abundance of native fishes and negatively correlated with diversity and
abundance of nonnative fish. The strong inference is that the nonnatives are maladapted to survive
intense and frequent (annual, at least) flooding in contrast to the natives. Having fewer predators
increases recruitment of natives, and over time allows the natives to persist in greater abundance
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than nonnatives (Figure 15). The work of Meffe and Minckley included the Virgin River and other
tributaries of the Colorado River, but none in the upper basin. Thus, while the data are not directly
applicable, the relationship probably holds. Indeed, Hawkins and Nesler (1991) correlated lower
ratios of nonnatives to natives with high peak flows in the Yampa River and red shiner populations
declined after years of high spring flows in the Colorado River (Osmundson and Kaeding 1991).
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Figure 15. Graphic models of the dynamic relationship between native and nonnative fishes in
regulated (A) and unregulated. (B) arid-land streams. A: In a regulated stream, native fishes (solid
line) typically decline and disappear upon introduction (x) of nonnative fishes (dashed line). B: In
a free-flooding stream, native fishes similarly decline after nonnatives appear, but flooding (arrows)
reduces nonnative populations to levels that pennit recovery of native fishes. During intertlood
periods, population size and range of nonnative fishes again expand and negatively impact native
species until the next flood. If flooding occurs frequently enough, long-term coexistence may
occur as a dynamic equilibrium. K = carrying capacity of the stream for native fishes. (From
Minckley and Meffe 1987.)

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