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This Year's Early Zooplankton Arrival Bodes Well For Salmon
Columbia Basin Bulletin
July 20, 2007
The early arrival of subarctic zooplankton -- including unusually high numbers of copepod species rarely seen in Oregon -- is providing a smorgasbord for offshore salmon and other species of fish, according to researchers conducting a salmon survey from Newport, Ore., to LaPush, Wash.
This is the 10th year researchers have conducted the survey of juvenile salmon and preliminary results suggest that numbers of both juvenile coho and juvenile chinook surveyed this spring were the highest they've recorded.
"We'll know more when we crunch the final numbers, but it certainly looks like a banner year for salmon survival -- primarily because of a bountiful supply of the right kind of food," said Bill Peterson, a fisheries biologist with NOAA who is based at Oregon State University's Hatfield Marine Science Center in Newport.
The juvenile salmon surveys, conducted in May, June and September, include the waters from the central Oregon coast north to the tip of Washington state.
Based on a long-term ocean observing program, which Peterson initiated off Newport in 1996, it has become clear that juvenile salmon respond quickly to changing ocean conditions.
"When the ocean is in a cool phase, such as existed from 1999 to 2002, juvenile salmon survival was high and adult returns were very high one year later for coho, and two years later for chinook," said Peterson, a courtesy professor in OSU's College of Oceanic and Atmospheric Sciences. "After ocean conditions suddenly changed in autumn 2002 to a warm phase, salmon returns immediately began to decline."
The ocean off Oregon has begun to cool once again, starting in July of 2006, after nearly four years of warm ocean conditions, said Peterson.
Cooler waters bring northern species of copepods into the region to feast on phytoplankton blooms triggered by summer upwelling. Copepods are small crustaceans that are major links in the food chain that supports salmon, other fish, whales and seabirds. Peterson's research suggests that northern species -- which are lipid rich -- provide better nutritional benefits for their consumers than southern copepod species that are prevalent during warm water regimes.
"This year, we've experienced one of the earliest biological transitions to 'summer' conditions in recent decades," Peterson said. "The subarctic zooplankton not only arrived extremely early, we are seeing unusually high numbers of a group of copepod species rarely seen off Oregon. These copepods are bigger than our usual 'local' species, and pack on even more lipids.
"The transition began in March this year, the earliest we've recorded during the 12 years of observations made off Oregon," Peterson added. "The two other years when the zooplankton arrived anywhere near that early – in 1970 and 1972 – were characterized by very high salmon production."
Among the seldom seen copepod species visiting Oregon this year are Neocalanus plumchrus, flemingerii, and Neocalanus cristatus.
"Whether this means we're experiencing a greater influx of subarctic water than usual, or whether we're getting normal water transport that happens to have a greater abundance of copepods -- we don't know," Peterson said. "In either case, it's good news for the fish that feed on them, particularly some species of groundfish and sablefish (black cod), which target Neocalanus.
"Of course," Peterson added, "we must see how the ocean responds during the remainder of the summer months before offering more firm prognostications."
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