NEWPORT, Ore. – 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 other creatures.
“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 copepods.
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 football field.
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 1998.
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.”