Understanding Out-Of-Subbasin Effects for Oregon Subbasin Planning
with particular reference to Ecosystem Diagnosis and Treatment assessments
Oregon Technical Outreach and Assistance Team |
February 27, 2004
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Introduction
Subbasin planning, by definition, is focused on the major tributaries
to the mainstem Columbia and Snake rivers. However, many focal species
migrate, spending varying amounts of time and traveling sometimes
extensively outside of the subbasins. Salmon populations typically spend
most of their lives outside the subbasin. Unhindered, sturgeon will spend
short periods in the ocean. Lamprey typically spend most of their life as
juveniles in freshwater, but gain most of their growth in the ocean.
Planning for such focal species requires accounting for conditions during
the time these populations exist away from their natal subbasin.
Out-of-subbasin effects (OOSE) encompasses all mortality factors from
the time a population leaves a subbasin to the time it returns to the
subbasin. These effects can vary greatly from year to year, especially for
wide ranging species such as salmon. Out-of-subbasin factors can be
natural in origin (e.g. ocean productivity), human-caused (e.g. fisheries)
or a combination (e.g. mainstem survival is dependent on both mainstem
flows and dam operations). Because of the richness and depth of
information available for salmon outside their natal subbasins and because
of the scarcity of information available for other anadromous focal
species, the remainder of this report describes out-of-subbasin effects
for salmon only.
This report is organized into four main sections:
Sections 1 and 2 describe, in qualitative terms, the OOSE structure of
the EDT model and environmental cycles which cause salmon survival to vary
widely.
Section 3 describes quantitatively OOSE survival estimates under base
period conditions and an expected survival range to represent
environmental variation.
Section 4 offers guidance for evaluating subbasin plans in light of
OOSE survival and variation. The following discussion draws from existing
data and previous analyses. It is a summary of existing knowledge and
hypotheses. The following discussion is confined to OOSE pertaining to
salmon populations, because of data limitations for other migratory
species.
Particular attention is given to out-of-subbasin effects as represented
in the Ecosystem Diagnosis and Treatment (EDT) model because this is the
most commonly used tool for developing assessments for salmon during this
round of subbasin planning.
Although much of the following discussion centers around the EDT model,
the final recommendations can be used with any assessment tool.
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