It
is generally accepted that climate change, with its increasing temperatures, will
have negative effects on BC salmon. DFO put out a paper in 2009 that studied
more than 350 related papers, covering Korea, Japan, Russia, Alaska, BC, WA, OR
and CA: http://www.npafc.org/publications/Special%20Publications/LRMP_Synthesis.pdf.
Beamish and Riddell, well-known names to sport anglers, took part. Do read it
as it is much more than I could summarize along with my own observations in an
article of this length. Use caffeine, too.
Factors
include: offshore weather patterns, decadal shifts in the Aleutians, winds,
ground water discharge, iron concentration, El Ninos/La Ninas, ocean currents,
temperature, ice cover, ocean migration patterns, run-timing, interspecies
competition, coastal upwelling, ocean acidity, zoo- and phyto-plankton effects and
then in freshwater, precipitation and form of precipitation, snow pack and snow
melt, increase in ice-free periods in lakes, temperature, size and timing of
freshet, composition of stream- or river-type chinook, coastal versus lengthy
migration into interior rivers and so on.
Surprisingly,
commercial catches have risen dramatically in Russia and climate warming is
seen as a good thing into the middle of the 21st century – because ice
effects in fresh and saltwater depress salmon numbers – while competition
between chum and pink fry results in size and productivity differences greater than
other factors right now. Similar ‘local’ variations occur, and sometimes
opposite results can occur in different regions from the same stressor.
Sockeye
are the first species to come back, and can be as early as April in the Hobiton
River on Van Isle, May to September in the Somass, May to June in Skeena and
Nass, and from early June to September in the complex, multi-component Fraser
run. Sockeye are the most sensitive to temperature, and diversion from west
coast to Johnstone Strait can result from a one degree temperature change. Fraser
River entry is also partly triggered by water temperature. In fresh water,
sockeye tolerate 20 degrees C, and then begin dying. I once stood on a balcony over-looking
the Somass confluence and the bottom of the river was littered with what looked
like silver bars. It was sockeye dying and little wonder, it was 42 C in the
shade where we sat in Margaritaville, sweating like pigs, doing nothing.
The
farther a run must go upstream, sockeye to the interior, for instance, the greater
the pre-spawn mortality with respect to temperature; but greater marine fat
levels brought back into the Fraser result in lower mortality, implying that
several factors can affect the portion of escapement that successfully spawns. You
will recall Dr. Kristi Miller’s work on the Viral Signature – meaning disease –
of Fraser sockeye can result in up to 90% pre-spawn mortality.
And
if there is greater ice or rain precipitation, eggs can be wiped out. And
sockeye typically spend a year or so in a lake before migrating. Higher temperatures
are thought to result in higher fry mortality in saltwater because they may be
too small to survive the ocean. Longer periods of sunlight on saltwater are
consistent with greater algal blooms, in Georgia Strait, associated with higher
mortality of smolts. And when the ocean is warmer, sockeye don’t grow as well,
and thus do poorer on entering rivers to migrate the distances.
The
Fraser River accounts for 30- to 40-% of all BC salmon production. Because
numerous stocks of sockeye, pink and chum are near the southern limit of their
range, the early impacts of climate change should be detectable in these stocks
first. Warm water during spawning results in earlier hatching of fry and higher
fry to smolt mortality.
Chinook
with their large bodies have difficulty entering coastal rivers depleted by
long, hot, summers, with a lack of precipitation. The same can be said for
their and coho fry surviving a long hot summer in rivers. Poor development in
rivers leads to coho, sockeye and chinook doing poorer in saltwater. It is not
yet clear whether the mechanism that causes ocean-weather regimes to shift will
be exacerbated or muted by increasing levels of greenhouse gasses.
Coho
come on the tail end of chinook runs, but tend to hang on beyond all other
species, waiting for the high rain falls of late autumn and even winter before
entering side-streams where they preferentially spawn. Less rain, means fewer
coho, which are the second most temperature sensitive of the five species,
because the side-streams become isolated pools in summer, with coho fry
frizzling in summer temperatures, waiting for fall flows to escape. Most of our
rivers have had their trees logged in the past century, resulting in very open,
gravel moonscapes that further elevate temperature. Go look at the San Juan for
such a devastated river. On the other hand, walk the easy trail and pretty Big
Qualicum with its forest cover intact and cooler summer flow. Vastly different
productivity.
Where
it rains is important, too. I have stood on a gravel bar extending from a side-stream,
measuring 25 by 20 by 12 feet deep. Four days later, because the main-stem had
received much rain, but not the tributary’s watershed, the entire tongue had
been blown out and the water was 12 feet deep. The higher and more concentrated
the rain, the greater the problem.
Chum
are notoriously poor at spawning in good locations. They tend to spawn on the
highest rains of fall and when the river drops, up to 90% of eggs are wasted.
So, less, rather than more rain, would conserve them, forcing them to spawn
within the river’s usual banks.
It
has also been shown that BC populations north of 50- to 55-degrees latitude
oscillate in ocean numbers differently from those of more southerly rivers. Warmer
weather allows cold water predators like hake and mackerel to move north and
eat more salmon. Predation is a big problem, even in Alaska where 75% of Prince
William Sound pink fry are lost to predation during their first 45- to 60-days
in the ocean.
Temperature
differences in the north east Pacific play a role in sorting out different
salmon species to different areas. Along with higher temperatures above the
water, currents flowing north to south split the near shore and off shore
regions and also distribute salmon for foraging. Higher temperatures will
influence marine distribution.
Salmon
also stray from their own rivers by as much as 10%. Pink and sockeye are now
reported in the Beaufort Sea. Chinook are the least temperature-related
strayers. I have witnessed pinks and sockeye in rivers where there are no historical
runs. Oddly, I have noticed sockeye – because they are so easily identified as
red fish before coho turn – spawning in the same patch of gravel in succeeding years,
even though the river has no identified sockeye run.
There
has been a decline in hatchery coho in Georgia Strait since the mid-‘80s, while
wild coho have remained stable but at low levels. Growth, survival and abundance
occur earlier in the year for wild coho than hatchery coho. Growth between July
and September is inversely related to marine survival, indicating that faster
and earlier growth may improve lipid storage, increasing the chances of
survival over the winter. This study suggests that fish farms have caused a 50%
decline in salmon numbers: http://fishfarmnews.blogspot.ca/2013/01/fish-farms-kill-more-than-50-of-wild.html.
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