Ocean conditions during
2008 for many fish species in the Pacific Northwest, including
chinook salmon, were greatly improved because of a huge cold
water influx that settled in across much of the northern
Pacific Ocean -- a phenomenon not seen on this scale in years.
In fact, scientists who surveyed near-shore waters from
Newport, Ore., to LaPush, Wash., this year found the highest
numbers of juvenile chinook salmon they've encountered in 11
years of sampling.
The reason may be traced to the Pacific Decadal
Oscillation, a pattern of climate variability that
historically has shifted between warm (positive) and cool
(negative) regimes over cycles of 20 to 30 years. During 2008,
the PDO was the most negative it has been since 1955,
according to Bill Peterson, a NOAA fisheries biologist at
Oregon State University's Hatfield Marine Science Center.
"We usually see cold water conditions for a few months once
upwelling begins in late spring and early summer," said
Peterson, who has a courtesy appointment in OSU's College of
Oceanic and Atmospheric Sciences. "Since April of 2007,
though, we've been in a constant 'summer-state' ocean
condition, which is something we've never seen in more than 20
years of sampling. And we're not sure why."
Strong, continual upwelling has fueled phytoplankton growth
that forms the basis of the marine food web. Cold water has
drawn a huge biomass of northern copepods from the Gulf of
Alaska, and these zooplankton species have high fat reserves
that provide a rich diet for anchovies, herring and other
baitfish, which in turn become prey for salmon, ling cod and
"The ocean is thick with these large copepods, which
accumulate fat as a way to survive the winter," Peterson said.
"When the Pacific Decadal Oscillation is in a positive phase
and warmer water moves into the coast from offshore and the
south, the copepods we see are species that are smaller and
don't retain lipids."
Peterson said anecdotal evidence from other researchers at
OSU's Hatfield Marine Science Center suggests that recruitment
for juvenile ling cod and other rockfish was extraordinary in
2008. Seabirds, including pelicans and a large murre colony at
Yaquina Head, were healthy and well-fed. And there was a large
population of sand lances -- a small baitfish that feeds on
If there is a downside, Peterson says, it is that the
survey didn't find as many juvenile coho salmon in 2008 as the
scientists had hoped. The number of juvenile chinook, on the
other hand, was 2.4 times higher than any other survey
recorded in the past 13 years, Peterson said. The scientists
used an array of nets in their survey, including a trawling
net as tall as a five-story building and as wide as half a
Though 2008 has been a banner year for ocean conditions --
and many fish species -- it is too early to know what the
future holds for ocean conditions or fish runs. The Pacific
Decadal Oscillation has been shifting more rapidly between
warm and cool phases, possibly in response to climate change.
A positive phase, characterized by warm, less-salty water,
occurred from 1925 to 1947, followed by a negative phase of
cooler, saltier water from 1948 to 1976. Then another positive
phase took over and lasted through the powerful El Nino of
Since then, however, the regimes have been much shorter.
The PDO was negative from 1999 to 2002, positive from 2003 to
2006, then abruptly shifted to cooler waters during the last
two years. Will this latest cold-water regime last two years
or two decades?
"That's the million dollar question," Peterson said.
Peterson and his colleagues have received a grant from NASA
to track the source of the cold water to see if it has
circulated from the Gulf of Alaska through an advection
process, or is the result of a different upwelling pattern,
bringing deep water to the surface. However, sea surface
temperatures haven't dropped as much as temperatures lower in
the water column.
Temperatures recorded this year at a sampling station five
miles west of Newport, at a depth of 50 meters, were the
coldest in the 13 years they've been measured. This suggests
to Peterson that the ocean is becoming more stratified, which
is consistent with climate change models. Those same models
also suggest more annual variability in ocean conditions.
"The year 2005 was one of the worst in history, as delayed
upwelling caused a food shortage that led, among other things,
to the collapse of the Sacramento River chinook salmon run,"
Peterson said. "In contrast, 2008 has been one of the best
years on record and though it's a generality, cold water
usually means good things for salmon.
"We just don't know how long this is going to last."