9378

• UCREFRP Catalog Number: 9378
• Author: Nesler, T. P.
• Title: Recovery of the Colorado River Endangered Fishes
• USFW Year: 2000.
• USFW - Doc Type: Biological recovery goals and criteria for Colorado pikeminnow, Humpback chub, Razorback sucker & Bonytail.
• Copyright Material: NO

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

habitats and ecological requirements have existed over the same time frame to
support these populations. These habitat and ecological conditions need to be
protected in some form. The institutional programs being implemented that
maintain these conditions need to be formalized in long-term agreements or
regulations. It is also reasonable to assume that the five listing factors are being
adequately addressed in the current environment and any threats are only
potential ones that are not exerting a negative influence and causing a declining
trend in the species' status. Long-term agreements and conservation
management plans as criteria for delisting provide a mechanism for protection of
what has proven to be the best combinations of flow (quantity/regime)
management, nursery habitat protection, instream passage, and nonnative fish
control to sustain the populations of the listed fishes required for recovery.

Species Status and Trends

A review of the current biological status of these species is necessary to
evaluate their condition relative to federal definitions of "endangered" or
"threatened", and to place proposed recovery goals into context. Under ESA 16
U.S.C. Section 1532, "endangered" is defined as "...in danger of extinction through
all or a significant portion of its range... ", and "threatened" is defined as ".. . likely to
become an endangered species within the foreseeable future throughout all or a
significant portion of its range." These definitions imply species documented to be
in declining trends toward eventual extinction, or species so limited in abundance
or distribution as to be vulnerable to local extirpation and extinction. A species that
is extirpated over a significant portion of its range, but stable or increasing and
secure within the remainder of its range may be interpreted under the purpose of
ESA and definition of "conservation" to be a candidate for delisting. The purpose
of this review of biological status for each of the listed fish species is to identify
declining trends or indices suggesting an adverse population condition, or a
positive status and trend indicating a change in federal listing status is warranted.

Colorado pikeminnow

Species status and trend Mark-recapture and length frequency data were.
available from 1990-1997 for the Colorado/Gunnison rivers and from 1991-1997
for the Yampa/Little Snake, White, and Green/Duchesne/Price rivers. These data
enable population estimates, recruitment and length frequency distributions to be
developed for each population segment from 1992-1997. Attributes of data used
and population estimates are provided in Appendix Tables A-1through A-4.

This species is well distributed in Upper Basin rivers. No losses in
distribution have been noted, and recently, passage of late-juvenile/early adult fish
at the Redlands passage appears to be increasing their abundance in the
Gunnison River. Augmentation stocking in the San Juan River may improve the
distribution of Colorado pikeminnow. Estimates of population size and fish/mile for
Colorado pikeminnow in these rivers appear to be stable (Colorado, Yampa) or

7