Blame for declining runs
of Pacific Northwest salmon has been cast broadly: habitat
loss from logging and development, an abundance of predatory
sea lions, power-generating dams, terns and other coastal
birds that prey on juvenile fish, and over-fishing by
commercial and sport fishermen.
But no factor is more
critical to salmon prosperity than ocean conditions, experts
say, and the complex interaction between biologically distinct
groups of salmon and changing ocean habitats has created
challenges for resource managers.
At the same time a projected huge run of spring chinook
salmon are entering the Columbia River, fishing on one of its
major tributaries -- the Willamette River -- has been closed
because of a low estimate of returning fish. And offshore
salmon seasons are either shut down or sharply curtailed along
the entire West Coast this spring and summer because of a
projected historic low return of fish to the Sacramento River
The common denominator in the good and bad runs is the
Bill Peterson, a fisheries biologist with NOAA who is based
at Oregon State University's Hatfield Marine Science Center,
says this year's salmon debacle can be traced back to unusual
ocean conditions in 2005. A delay in the ocean upwelling
caused ocean conditions "to collapse."
"The delayed upwelling off the Oregon coast meant that in
the critical time when juvenile salmon were entering the
ocean, there was nothing for them to eat – and most of them
died," said Peterson, who is a courtesy professor in OSU's
College of Oceanic and Atmospheric Sciences. "But you don't
see the impact until two or three years later, when the fish
should first begin returning as adults."
Wind-driven upwelling brings nutrients from deeper water to
the surface and fuels phytoplankton blooms. Lipid-rich
copepods and other zooplankton feed on the tiny plants, and in
turn are consumed by anchovies, sardines, herring and other
small fish that are staples in the diet of salmon and other
fish. The delay in upwelling was caused by late arrival of
seasonal winds, according to researchers at OSU, who published
their findings in the Proceedings of the National Academy.
The delayed upwelling can explain why most fish runs are
plummeting, yet fisheries managers are predicting a huge
number of spring chinook bound for the Columbia River this
year. Why? The answer, Peterson says, can be found by tracing
where juveniles from different river systems go once they
enter the ocean.
For the past 10 years, Peterson has participated in a
research project funded by the Bonneville Power Administration
that analyzes the distribution of juvenile salmon off the West
Coast and uses genetic tracking to determine their river
origin. Juvenile fish from many of Oregon's coastal rivers,
along with those from the Willamette River and the Sacramento
River, congregate just off the Oregon coast once they leave
their river systems.
When the ocean collapse came in 2005, most of those fish
"But Columbia River spring chinook don't stay off the
Oregon coast," Peterson said. "In our 10 years of sampling,
we've only caught a few Columbia River juveniles just off our
coast, so it's obvious they go somewhere else. If you look
this year at chinook salmon in Alaska, they're doing well. So
it's possible that Columbia River juveniles head to the same
place as Alaska juveniles."
Peterson speculates that perhaps young Columbia River
salmon may migrate toward a unique ecosystem several hundred
miles off the Northwest coast. In that deep, cold water,
lipid-rich fishes known as myctophids, or "lantern-fish,"
provide a bountiful diet for a variety of marine life. These
fishes are "very abundant" in the mesopelagic zone, he added,
and could provide a rich forage base for young chinook salmon.
"It's just a theory at this point," he said. "We need to go
out there and sample for juvenile salmon. But the situation
this year underscores how fascinating research on salmon can
be. We used to have a lot more genetic diversity in our salmon
runs. They used to spawn at different times and hang out
offshore at different times. We may be paying for the loss of
Ocean conditions off Oregon in 2006 and 2007 were somewhat
better for salmon survival, but still were less than ideal.
The good news, Peterson says, is that the influence of La Niña
over the winter has created what appear to be excellent ocean
conditions thus far in 2008. But, he added, it's premature to
"The system can't recover from a near-complete collapse in
one year," Peterson warned. "There may not be enough adults in
the streams to repopulate the runs. We need three or four
years of good conditions before we can breathe a little