Viability of ESUs Containing Multiple Types of Populations
April 8, 2005 | document ISAB 2005-2
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Introduction
This is the Independent Scientific Advisory Board's report and report
submittal letter answering five questions asked by NOAA-Fisheries
Northwest Science Center on January 25, 2005, about evaluating the
viability of Evolutionarily Significant Units that contain hatchery and
natural or resident and anadromous populations.
To answer these questions, the ISAB first defined a ?Viable ESU? as
a group of populations existing together as a metapopulation that as an
entity is self-sustaining for the foreseeable future. A Viable ESU needs
to be in an ecologically and evolutionarily functional state sufficient
to: rebound from periods of low abundance or even very local extirpations
that are expected natural phases of population cycles; avoid the loss of
genetic and/or life history diversity during short-term losses in
abundance; fulfill key ecological functions that are attributable to the
species, such as nutrient cycling and food web roles; and provide for
long-term evolutionary adaptability to changing environmental conditions.
Evaluation of ESU viability should rest not only on the numbers of
component populations or on the abundance and productivity of those
individual populations, but also should be based on the population
dynamics within the ecosystem as a whole. This concept of ESU viability
does not tolerate the loss of either the anadromous or resident life
history form from any given ESU, because that loss would represent a loss
in diversity for the ESU that would put its long-term viability at risk.
In addition, although this concept of ESU viability may not preclude the
presence of hatchery-origin individuals within an ESU, it does preclude
the dependence of ESU viability on hatchery-origin individuals, and it
precludes the replacement of the original wild population with a hatchery
derived one. This argument is based on scientific evidence that an ESU
needs to contain viable, naturally adapted populations inhabiting a
variety of different natural habitats, interconnected as a metapopulation,
if that ESU is to fulfill the entire complement of ecological and
evolutionary interactions and functions.
Establishing the policy boundaries for ESU viability assessment is
likely to be as important to the eventual outcome as the method used in
the assessment. The natural populations associated with integrated
hatchery programs are generally not themselves viable and the habitats
upon which they depend are usually inadequate. If the policy decision is
made that self-sustaining natural populations are not required for an ESU
to be viable, it is likely that the number of extant natural populations
will continue to decrease and the impetus behind current efforts to
improve habitat conditions will be greatly reduced. The ISAB believes that
the current science indicates that ESUs dependent upon hatchery production
cannot be viable ESUs according to the ISAB's definition of this term uses
in this report. Therefore, a policy that recognizes such ESUs as viable
would need to use a definition of viability much different from the one
the ISAB is using. The biological validity of such a definition would be
questionable.
Complete ISAB findings and the answers to the NOAA questions are in the
report.
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