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

based on available data and proposed values were presented to describe an
"improving condition" desired for each parameter for each population. Species'
distribution, population estimates, density, recruitment rate,. survival rate, and age
composition were estimated using data available through 1991. Since then, the
Recovery Program implemented a fish tagging effort using Passive Integrated
Transponder (PIT) tags to mark all endangered fish captured or stocked.
Compared to the previous use of externally-fastened Carlin tags, loss of PIT tags
from marked fish is negligible, and enhances our ability to identify individual fish in
the population, increase the number of marked fish in the population, and estimate
population size. In the eight years since the Colorado IROs were developed, new
information based on these PIT tags is available to update and refine certain
population parameters, including population size and recruitment. Other studies
within the Recovery Program provide information such as adult survival rates for
Colorado pikeminnow and point estimates of population size for select species in
select river reaches for comparison. On the other hand, age data and survival
estimates based on age composition of individual populations have not been
updated since 1992. The premise of this approach is that the fish data available
from standardized monitoring and population estimation sampling is sufficient to
develop measurable criteria for downlisting and delisting goals.

The stated purpose of the Endangered Species Act (ESA) is "to provide a
means whereby the ecosystems upon which endangered species and threatened
species depend may be conserved" (ESA 16 U.S.C. 1531). This purpose does not
imply that the species must be restored fully to its historic range. The definition of
"conserve" within ESA is "to use and the use of all methods and procedures which
are necessary to bring an endangered species or threatened species to the point
at which the measures provided pursuant to this chapter are no longer necessary
(ESA 16 U.S.C. 1532). It is important to note that "recovery" is not defined within
ESA, but could be interpreted to be the "poinf' referred to in the definition of
conservation. Recovery is a species-specific attribute bounded by the definition of
"conservation" within ESA. Recovery may be defined as restoration of a target
species demographic status and trend to a condition where it is no longer in
danger (threatened or endangered) of becoming extinct. Restoration of the
species to greater levels of distribution and abundance within its historic range
(beyond recovery from a decline toward extinction and within a secure, supporting'
ecosystem) is not the intended purpose of ESA. The approach used here focuses
on inclusion of populations and their habitat where a potential for persistence is
feasible based on existing biological data.

The over-ridinQ criterion associated with recovery is that recruitment
to adult populations is Qenerated throuQh natural reproduction in the wild.
Additional definitions of recovery for these fishes can be reduced to key population
parameters, or criteria, including number of populations, distribution, abundance,
recruitment to the adult population, and population size structure. All of these
parameters can be determined or estimated annually from field data using
consistent methodology. The goals established for each of the listed fish species

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