[env-trinity] CBB: Warming Coastal Ocean Temperatures May Lead To Negative Effect For Salmon 'Recruitment' By Reducing Prey

[Sari Sommarstrom]

THE COLUMBIA BASIN BULLETIN: Weekly Fish and Wildlife News

www.cbbulletin.com

October 9, 2015                Issue No. 766

 

Warming Coastal Ocean Temperatures May Lead To Negative Effect For Salmon
'Recruitment' By Reducing Prey

 

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 coastal
ocean."

 

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#.VhaOsPlVik
o)

 

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 icthyoplankton biomass.

 

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 date.

 

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 indicators.

 

"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

 

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