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
Urbanization upstream of Hope. Noting that more
than two-thirds of British Columbians live in the
Fraser River basin, the researchers identified
three ways in which urbanization and the related
built environment have the potential to affect
the freshwater habitats of Fraser River sockeye
salmon. First, residential, business, and industrial
development and road-related construction can
increase the amount of impervious surfaces in
urban watersheds, which affects rates of interception,
patterns of runoff, and, in turn, the magnitude
and timing of instream peak and low flows.
Second, construction of roads and buildings along
stream channels and lake foreshore areas has the
potential to reduce riparian vegetation, channelize
streams, and block access to habitats. Finally,
roads, stormwater runoff, and municipal and
industrial effluents have been known to alter water
quality in watercourses across the Fraser River
basin by changing concentrations of sediments,
nutrients, and contaminants. Nevertheless, the
researchers concluded that urban environments
have a relatively small footprint within watersheds
and riparian zones that influence sockeye spawning
and rearing habitats, the majority of which are
upstream of Hope. 28
Agriculture. Livestock grazing and crop production
can lead to physical alterations of streams, riparian
zones, and flood plains. Cattle crossing through
streams can potentially increase sedimentation,
destroy spawning redds, and destabilize stream
banks or widen stream channels. Removal and
disturbance of vegetation in the riparian zone can
reduce shading and increase water temperature,
affecting spawners and eggs. Direct removal of
water from groundwater and surface water supplies
for irrigation and livestock purposes can be a
significant stressor. Finally, agricultural activities
can have a significant impact on the water quality
of streams and lakes by increasing biochemical
oxygen demand; introducing pathogens; and affecting
concentrations of sediments, nutrients, and
pesticides into waterways. However, the researchers
concluded that agriculture has a relatively
small footprint within watersheds and riparian
zones that influence sockeye salmon spawning
and rearing habitats. 29
Water use. Potential impacts of water use on sockeye
salmon are related to alterations in water flows and
temperatures. Surface water use can reduce instream
flows that constrain access to spawning habitats
or, in extreme cases, de-water redds. Extraction of
groundwater for irrigation can reduce flows into
streams, increasing water temperatures that affect
sockeye salmon adults and eggs. 30
Nelitz and others concluded:
Our assessment of the cumulative effect
of freshwater stressors suggests that the
recent declines in Fraser River sockeye
salmon are unlikely to be due to changes in
freshwater habitats … An important piece of
evidence in reaching this conclusion is that
juvenile survival has remained relatively
stable across CUs where data are available
(see Peterman et al. 2010 [Exhibit 748]),
even though there is substantial variation in
stressor intensity across CUs.* In the literature,
there is strong evidence that the stressors
examined here can lead to declines and extinctions
of populations in a variety of species,
including sockeye salmon. A consideration of
individual stressors … suggests that the highest
levels of overall stress are generated by forest
harvesting and roads, while water use and
large hydro also generate significant stress for
individual CUs. 31
During the evidentiary hearings, Mr. Nelitz
testified that the timing of some stressors does not
coincide with the timing of the pattern of decline
in sockeye salmon. 32 For example, the mountain
pine beetle infestation did not become serious until
2003, at least a decade after the Fraser River sockeye
decline began. Similarly, in many watersheds the
intensity of forestry disturbances has been relatively
stable. 33 Mr. Nelitz also observed that, generally,
the longer the migration distance of a Fraser River
sockeye stock, the greater its decline. 34
Forest harvesting impacts
Dr. Peter Tschaplinski, a research scientist with
the BC Ministry of Environment, testified that a
number of potential forestry-related impacts on
* The conclusion that juvenile survival has remained relatively stable across CUs is based on data from only nine stocks. See Exhibit 748, p. 2.
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