While the Pacific Decadal Oscillation is the
most important factor in determining how many salmon return from the ocean to
streams in the Northwest, a series of other more regional environmental factors
also influence that return, according to a recent study.
The study found that multiple, inter-related
ecological pathways (environmental factors) can strongly influence Oregon
coastal coho salmon abundance, with the most important factor being the PDO, an
index of large-scale climate variability in the North Pacific Ocean.
Among those pathways (17 in all, including two
biophysical pathways) coastal ocean temperature (sea surface temperature -- SST)
and juvenile salmon prey biomass (the biophysical pathway) had the strongest
effects on recruitment of the salmon.
Having less impact on recruitment were the
North Pacific Gyre Oscillation (NPGO) and the Oceanic Nino Index (ONI).
“We found that in years when the coastal ocean
was warmer than average there also tended to be reduced salmon prey biomass and
lower salmon recruitment levels compared to cool ocean years,” said researcher
Michael Malick, PhD Candidate, School of Resource and Environmental Management,
at Simon Fraser University. “From a climate change perspective, this result
suggests that warming coastal ocean temperatures may have a negative effect on
coho salmon recruitment by reducing available prey resources for salmon in the
There is a degree of uncertainty associated
with the environmental relationships, Malick added. “For example, our results
indicated that when coastal ocean temperatures were above average there is
still a 1 in 4 chance that recruitment would be above average,” he said.
The study, “Accounting for multiple pathways
in the connections among climate variability, ocean processes, and coho salmon
recruitment in the Northern California Current,” was published online August
28, 2015 in the Canadian Journal of Fisheries and Aquatic Science (http://www.nrcresearchpress.com/doi/abs/10.1139/cjfas-2014-0509#.VhaOsPlViko)
Malick’s co-authors are Dr. Sean Cox
(Associate Professor, Simon Fraser University) and Dr. Randall Peterman
(Professor Emeritus, Simon Fraser University), both in the School of Resource
and Environmental Management; Dr. Thomas Wainwright (Research Fishery
Biologist, NOAA Fisheries, Newport, OR); and Dr. Bill Peterson (Oceanographer,
NOAA Fisheries, Newport, OR).
The physical network of ecological factors
includes such factors as PDO, SST,
ONI, NPGO, spring transition and upwelling.
“The spring transition variable is meant to
capture the timing of the change in ocean conditions that occurs between the
winter months when there is little to no upwelling off the coast of Oregon (in
fact there can be strong downwelling during the winter caused by southerly
winds) and the spring and summer months when there can be strong upwelling off
the coast caused by northerly winds,” Malick said.
The biophysical networks include copepod and
According to the study, in the physical
network of environmental factors, the two with the most impact on salmon
recruitment are cooler surface temperatures and an earlier spring transition
In the biophysical network, higher prey
biomass is associated with higher recruitment.
In the course of the analysis, the researchers
quantified the uncertainty among the environmental pathway relationships. For example, “there was a 71 percent chance
that recruitment would be 150,000 salmon or less when the PDO was in a warm
phase for the physical network and a 62 percent chance for the biophysical
network,” the study says.
“When the PDO was cool, the probability of
recruitment being equal to or below 150,000 was considerably less, with a 54
percent chance in the physical network and a 45 percent chance in the
biophysical network,” the study says.
Temperature may directly influence salmon in
the ocean, but it’s the increase in icthyoplankton biomass caused by lower
temperatures that links SST (the physical factor) and biomass (the biophysical
factor) to salmon abundance, according to the report.
The cooler water is associated with a northern
community of copepods with low species diversity, but rich with lipids, good
for fish growth. However, the warmer water is associated with a southern
community of copepods with high species diversity, but it is poor with lipids.
This probabilistic approach, where uncertainty
is expressed, is an “important factor in using ecological models to guide
decision-making,” the study says.
“From a management perspective, our research
indicates that environmental factors can be useful indicators of coho salmon
recruitment,” Malick said. “However, our results also suggest that focusing on
only a single environmental factor can be misleading due to inherent
uncertainties in the relationships between recruitment and environmental
“From a longer-term perspective, our findings
indicate that future data collection and research efforts should focus on
regional-scale oceanographic processes, for example, by obtaining more precise
estimates of coho salmon prey resources,” he concluded.
An overview and summary graphic of the
research can be found at: http://michaelmalick.com/research/bayes-network/index.html