9547

• UCREFRP Catalog Number: 9547
• Author: Tyus, H. M. and J. F. S. III.
• Title: An Evaluation of Recovery Needs for Endangered Fishes in the Upper Colorado River, with Recommendations for Future Recovery Actions - Final Report.
• USFW Year: 1999.
• USFW - Doc Type: Glenwood Springs, CO.
• Copyright Material: NO

Despite legitimate concerns about the extent to which present-day field studies of rare
species will provide an accurate representation of their life history requirements, there is
no alternative but to make the best use of such information. Field studies conducted
where a species is relatively abundant, and where the habitat is altered least (all habitat
~ now occupied by the endangered fishes has been altered some), are most likely to
provide an accurate view of life history requirements (discussed by Tyus 1992). The
optimal remaining habitat is closest to the conditions in which the native species
evolved, and presumably are the conditions in which the species are most likely to
maintain adaptive advantage over introduced species. Field studies in the UCRB have
~ tended to be very localized in focus, with the result that populations (or subpopulations)
of one species are treated almost as if they were separate species. A narrow
geographic focus for field studies can lead to a fragmented view of recovery needs.
Although local adaptations can and do occur, recovery efforts in general could benefit
from generalizations about and synthesis of life history needs, leading to a conceptual
~ model of life history.
The Green River system in the upper basin has long been identified as perhaps the
most suitable location to determine management measures necessary for recovery of
Colorado pikeminnow and razorback sucker, because it supports the largest riverine
~ populations of these species and because habitat in a major tributary, the Yampa River,
remains largely unaltered. Flow in the mainstem of the Yampa River is regulated little
and access to upstream habitat has not been blocked. The Grand Canyon in the
vicinity of the Little Colorado and Colorado rivers is the logical place to study the life
history needs for the humpback chub, because there is a large population sustained by
. natural recruitment. Information obtained from the more "natural° locations can be
supplemented, albeit cautiously, with observation from sites where habitat has been
altered, but where the species is relatively abundant. A good example is Lake Mohave,
AZ-NV, which supports the largest extant population of razorback sucker. The bonytail
presents a special challenge because it is not sufficiently abundant anywhere in nature
to afford opportunities for meaningful study.
Observations of behavior or habitat use for individuals at different stages of
development represent fragments of life history that must be assembled into a cohesive
story. The task is difficult because the subjects are hard to locate and there are
confounding factors, as mentioned previously. Nevertheless, a complete understanding
~ is important for the recovery effort because it can-help identify obstacles to recovery of
existing populations and sites with potential for restoring populations. The remainder of
the text in Part 2 of this report summarizes what is known about the life history
requirements of each of the four endangered fish species.

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