of wild chinook salmon from the Columbia River to northern Alaska is subject to
large-scale atmospheric and ocean circulation trends, especially the North
Pacific Gyre Oscillation, according to a recent study.
studies of coho, pink and sockeye salmon stocks have found that trends in
productivity for these stocks have more to do with localized ocean trends.
study also found a more alarming trend: the differences in timing and
productivity among the various wild chinook stocks are becoming more
synchronous, meaning that there are fewer variations and less diversity, all a
result of ocean trends that are caused by global climate change.
of chinook shows covariation on very large scales, from Oregon to Western
Alaska,” said researcher Brigitte Dorner, an independent fisheries scientist
who lives on Lasqueti Island in British Columbia. “This is unusual for salmon,
and it suggests that there are some factors operating on equally large scales
that influence chinook productivity. These factors are likely linked to
large-scale atmospheric and ocean circulation phenomena, which affect chinook
through mechanisms such as food availability and predator prevalence.”
said the link between chinook productivity and the large-scale circulation
patterns -- besides the NPGO, the study considered the Pacific Decadal
Oscillation and the location of the bifurcation in the North Pacific current as
it reaches North America -- is concerning for two reasons.
first is climate change, which is affecting the large-scale circulation
patterns in ways difficult to predict in the longer term.
we may expect that chinook productivity patterns may start to diverge from what
we have seen historically and therefore also become more difficult to predict,”
Dorner said. “One particular development that has been linked to climate change
is an intensification of the NPGO, with more intense phases of low and high
values. Assuming this trend continues, we can expect to see more of a
‘roller-coaster’ pattern of large swings in chinook productivity.”
second is that productivity patterns of separate populations have become more
synchronized, “meaning there is less ‘balancing out’ of declines by increases
elsewhere,” she said.
is difficult to infer causality without actually studying the direct mechanisms
by which large scale circulation patterns affect chinook productivity in more
detail, but just logically speaking, increased synchronicity is consistent with
what you would expect if factors related to large scale atmospheric circulation
patterns were becoming relatively more important as drivers of productivity,”
combination of increased synchronicity and intensification has potential for
serious impacts on chinook-dependent species as well as chinook fisheries,
“Spatial and Temporal patterns of covariation
in productivity of Chinook salmon populations of the Northern Pacific” was
published online last month in the Canadian Journal of Fisheries and Aquatic
co-authors are Matthew Catalano, professor, School of Fisheries, Aquaculture,
and Aquatic Sciences, Auburn University, and Randall Peterman, professor
emeritus, School of Resource and Environmental Management, British Columbia.
the recent changes (changes found during the period 1995 to 2009) – increased
synchronicity and extreme swings in productivity – may reduce the resilience of
chinook salmon to the effects brought on by climate change and the resulting
habitat modifications, the study says.
change appears to be driving the intensification in the NPGO, which in turn may
be responsible for the increased synchronicity at least to some degree, Dorner
the other side of the equation, increased synchronicity, especially when
combined with more extreme swings in productivity, would be expected to make
stocks more vulnerable to a variety of adverse factors, including factors
linked to climate change,” she said. “For example, if major flooding or drought
affects a stock or group of stocks at a time when populations throughout the
area experience a phase of low productivity, that has potentially more serious
and long-term consequences than the same event occurring during a time when at
least some of the nearby populations are doing well and can compensate for
local losses through recolonization, maintenance of genetic diversity, etc.”
study looked at 24 distinct stocks of wild, not hatchery, chinook salmon, even
though many of the stocks have a substantial hatchery component. The focus on
wild stocks was to permit a greater understanding of chinook survival dynamics
without the confounding influence of hatchery practices, the study says.
these stocks, run timing for both the juvenile and adult life history vary
widely. Outmigration for chinook differs with ocean-type (subyearlings) which
migrate in the first year in fresh water and freshwater type (yearling) which
spend their first year in freshwater, according to the study.
run timing also varies, with fish returning in spring, summer or fall.
the longer term that used 1981 to 2009 data, there appeared to be considerable
diversity among stocks in productivity patterns. There was an increase in
productivity throughout the 1980s followed by a period of decline and then
another sustained increase after 2000, the study says.
looking closer at shorter term data (1995 to 2009) there was a steep decline in
productivity beginning with ocean entry year 2000, but then a period of
recovery after 2005. That steep decline in the early 2000s was a trend most
widely shared among chinook stocks in the Northeast Pacific, the study says.
Between 21 and 22 of the 24 stocks studied had that downward trend, showing
that “broad scale ocean or climate-driven conditions reflected by NPGO have a
substantial effect on Chinook salmon productivity.”
increased synchronicity can be “expected to result in more year-to-year
variability in harvest levels and more frequent fishery closures because fewer
stock abundances will be high when others are low, especially since the
predominant trend in recent years has been towards lower productivity,” the
of the biggest challenges facing fisheries scientists and managers is the
non-stationarity of stock productivity (i.e., where the mean and/or variance
changes substantially over time),” the study says. “Regardless of whether such
changes occur because of altered ocean conditions or freshwater conditions, the
success of efforts to sustainably manage Pacific salmon harvests and rebuild
low-abundance populations depends on understanding the causes of changes in