The Uncertain Future of Fraser River Sockeye - Publications du ...

Cohen Commission of Inquiry into the Decline of Sockeye Salmon in the Fraser River • Volume 2
evident. To complicate matters further, some (but
not all) Fraser River sockeye stocks show dramatic
variations in abundance over a four-year cycle (a
pattern called “cyclic dominance”) that consists of
a dominant year, followed by a sub-dominant year,
followed by two much less productive years.
To these fascinating variations in Fraser River
sockeye themselves must be added similarly complex
variations in freshwater and marine habitat,
environmental conditions, and the myriad stressors
that affect sockeye differently, depending on the
geographical area and the life stage under consideration.
Moreover, exposure to stressors in one life
stage may not reveal their effects until a later life
stage, and stressors may interact in different ways at
different life stages.
In light of these complexities, it is prudent to
embark on this analysis bearing in mind the caution
voiced by the authors of Technical Report 1A,
Enhancement Facility Diseases:
It is tempting to think of a cause as a single entity,
event or condition which inevitably leads
to a specific outcome. This is rarely the case in
biomedical situations, especially when population
health and disease are being considered.
The presence or absence of a disease typically
requires a complex interplay of factors. When
referring to wildlife populations, Holmes (1995)
said, “Looking for a single, consistent cause for
population regulation is not only wishful thinking,
but also hinders our efforts to understand
population dynamics. Population regulation is
not only multifactorial, but interactions among
those factors are important; single-factor
experiments can miss important interactions.
In addition, the ecological context consistently
changes, so that regulatory processes track a
moving target; experiments can have different
results if the context differs.” 2
In the pages that follow, as much as the
evidence allows, I examine the various stressors
affecting Fraser River sockeye salmon according to
their different life stages, adopting a five-life-stages
categorization.
This chapter constitutes a summary of the evidentiary
record related to the decline that is before
this Commission. It is intended to accurately reflect
what the researchers wrote in their reports and what
witnesses said in their testimony. It should not be
assumed that I necessarily agree with or endorse
everything set out in this chapter of the Report.
Rather, it is a summary of what I read and heard.
My findings and conclusions respecting the causes
of the decline of Fraser River sockeye salmon will
come later, in the following chapter of this volume.
Life stage 1:
incubation, emergence,
and freshwater rearing
Incubation
After the long return journey to her spawning
grounds, the female Fraser River sockeye selects a
site for the deposit of her eggs (a redd), digs a nest
in the gravel substrate, and deposits 500 to
1,100 eggs, which are simultaneously fertilized
by an accompanying male or males. She then
covers the eggs by further digging and repeats
the digging and spawning process up to several
times. Finally, she covers the completed redd,
now containing two or several nests of eggs, and
then guards the redd site until near death. The
eggs develop in the gravel during the winter. In the
early spring, after about five months’ incubation,
alevins emerge from the eggs. A pronounced yolk
sac suspended below the body provides nourishment
for the next six to 10 weeks, depending on
water temperature. During this period, the alevins
remain in the gravel for protection from predators
and because they are poor swimmers.
Fraser River sockeye salmon are particularly
vulnerable during this incubation period. The
mortality rate during this seven-month period can
be 80 to 86 percent. 3 In the case of a spawning female
that lays 3,000 eggs, 2,580 may die during incubation
or soon thereafter. 4 Mike Lapointe, chief biologist,
Pacific Salmon Commission, identified the following
naturally occurring stressors that contribute to egg
and alevin mortality:
• Redds may be disturbed or destroyed by laterspawning
females, an action that may expose
the eggs within to a variety of stressors.
• High water flows may lead to scouring of redds,
exposing the eggs within.
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