[env-trinity] CBB: NOAA research shows how changing ocean conditions influence bird predation on salmon

Fri Aug 11 11:54:39 PDT 2017

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NOAA Research Shows How Changing Ocean Conditions Influence Bird Predation
On Salmon 
Posted on Friday, August 11, 2017 (PST) 

Interpreting relationships between species and their environments is crucial
to inform ecosystem-based management (EBM), a priority for NOAA Fisheries.
EBM recognizes the diverse interactions within an ecosystem -- including
human impacts -- so NOAA Fisheries can consider resource tradeoffs that help
protect and sustain productive ecosystems and the services they provide.

In the coastal ocean of California -- seabird predators, forage fish on
which they feed, and the survival of salmon out-migrating to sea are each of
particular interest, and an improved understanding of their interactions
could in turn improve the management of the ocean ecosystem, says the
agency. 

For example, in the California Current, understanding the interactions
between predator seabirds, forage fish in the coastal ocean and
out-migrating salmon from San Francisco Bay could improve the understanding
of salmon early survival in the ocean and a measure of the possible strength
of the year class return.

In the Gulf of the Farallones, new research by scientists from NOAA
Fisheries' Southwest Fisheries Science Center, Point Blue Conservation
Science, H.T. Harvey and Associates, University of California Santa Cruz,
U.S. Geological Survey and the U.S. Fish and Wildlife Service found that the
common murre, a small ocean seabird, can make a difference in the number of
salmon that survive to return as adults. This is especially true when ocean
conditions cause the murres to feed primarily on salmon and anchovy. The
research has been published online in the Journal of Marine Systems, and
will be included in the journal's October print issue. 

Large colonies of more than 500,000 common murres nest throughout the Gulf
of the Farallones, offshore of San Francisco. In typical years, with
nutrient-rich water welling up from the depths, the murres prey primarily on
young rockfish around their offshore breeding sites.

When ocean conditions change, and the upwelling falters, young rockfish that
are the typical prey for the murres become scarce. Then the murres switch,
feeding instead on adult northern anchovies found closer to shore. That's a
problem for the young salmon entering the ocean at these near-shore
locations, because the murres eat them too.

The finding documents one of the first examples of what biologists call
"bottom-up" influences -- changes at the base of the food web -- causing
"top-down" effects on West Coast salmon, such as an increase in predation by
a species higher in the chain, in this case the common murres.

"This is the first example we've found involving salmon where bottom-up
drivers are causing top-down impacts," said NOAA Fisheries research
biologist Brian Wells, lead author of the research. "The lack of upwelling
affects salmon in a top-down way."

The new research shows that salmon survival drops sharply in the years when
ocean conditions lead the murres to prey on anchovy and salmon. Even in
years when the murres are preying on anchovy, salmon comprise less than 10
percent of the diet of the murres; but the impact can be a significant
factor in the survival of salmon. The research concludes that predation by
the seabirds can make a difference in the number of salmon that survive to
return as adults. 

The salmon affected are primarily fall-run chinook, which are the primary
species supporting salmon fisheries off the California Coast. The research
helps reveal the complex relationships between species and their
environment, which in turn helps NOAA Fisheries anticipate and respond to
changes that affect fish, birds and people.

For example, the murres preyed heavily on anchovy and salmon in 2005, which
likely contributed to the collapse of the California salmon fishery in 2007
and 2008, the researchers found. Congress appropriated $170 million in
disaster relief for fishermen affected by the collapse.

NOAA Fisheries managers can use the details to make better decisions about
how best to protect and manage marine species.

"Understanding the dynamics behind these connections can help us anticipate
impacts to salmon, which are very important both economically and
environmentally," said John Field, a research fisheries biologist at the
SWFSC in Santa Cruz. "That can help fisheries managers make smart and
informed decisions about how to manage these species into the future."

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