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

squawfish. Although extremely high flows appear to be associated with weak cohorts of Colorado
squawfish and humpback chub, occasional extreme flooding needed to maintain channel
morphology and channel-floodplain interactions likely are critical for long-term survival of the
fishes. Indeed, the only recent incident of successful recruitment of adult razorback sucker
occurred when high flows reconnected riparian gravel pits to the mainstem Colorado River. On the
other hand, it is fairly clear that squawfish recruitment can occur over a very wide range of spring
flows, and squawfish spawning may be much less site-specific than is suggested by the literature, or
a very wide range of preferred. spawning conditions exist on the spawning bars where squawfish are
routinely found (e.g., Cleopatra's couch bar on the Yampa, Three Fords on the Green). Presence of
nonnative predators and reduced complexity of habitats needed by the different life history stages
of the endangered fishes (due to severing of channel-floodplain connections and encroachment of
riparian vegetation into the channel) further confound detennination of cause and effect. The
fundamental problem with respect to provision of flows to recover the endangered fishes is
balancing the many interactive effects in a manner that will favor the native fishes over the long term
(i.e., decades).
5) The phenologies (life histories) of the endangered fishes, as well as zoo benthos which
also have been studied in detail, are either directly or indirectly controlled by flow magnitude and
timing and the association between flow and temperature. However, relationships between flow,
channel configuration and thennal heterogeneity (cf., Ward 1984) have not been well integrated
conceptually or empirically or in the context of the various life history stages of the fishes. A
squawfish life history energetics model, for example, likely would be very helpful in this regard.
6) Stream regulation has introduced serial discontinuities (i.e., downstream extension of
cold water or rhithron environments) within the river continua of the Upper Colorado River Basin.
The location and persistence of these discontinuities are directly related to flow, and largely
detennine where the endangered and other native fishes can achieve a positive life history energy
balance (i.e., complete the life history with net recruitment of young at or above minimum viable
population size). Bear in mind that these fishes are adapted to potamon conditions and the length

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