Salmon and the Pacific Northwest environment have interacted in a two million year old feedback loop to the point where the two depend on one another.

Failed Feedback Loop Part 1 - Aborted Upwelling

For salmon—evolved as freshwater fish but habitually anadromous—the transition from freshwater to saline is crucial, tenuous and dependent on the seasonal upwelling of deep-sea water to the ocean surface off the coast of Oregon.

Jen, a lab technician at Oregon State University’s Hatfield Marine Center, says this surge of cold, deep-sea water to the surface is visible to the naked eye. “Bait balls,” she calls the indicators. By way of explanation, she points to the clusters of diving birds that dot the ocean surface near the research vessel, MS Elakha, five miles due west of her Newport Marine Center lab.

Upwelled deep-sea water is highly nutritious, packed with years of decomposed surface fauna refuse that has drifted to the ocean floor and been processed anaerobically or by bottom dwelling bacteria and crustaceans. The nutrients and cold water travel to the surface along flumes, spurring single algae along the way into multi-acre blooms.

During upwelling, microscopic deep sea plankton like copepods and krill rise along the water trails to feed on the algae blooms. Birds, like the ones Jen is pointing out, fish and larger mammals like seals and whales, in turn, come to feed on the plankton.

Bill Peterson thinks of Oregon's coastal upwelling at a global (in map at left) and local level (right). Globally, the regional five month upwelling is the convergence of ripple effects from phenomena in Alaska (PDO) and along the equator (ENSO) and local seasonal shifts in currents. At the local level (above, right) red and blue arrows indicate feeding interactions in the upwelling system. salmon (corner right) are eaten by predators and feed on zooplankton.
(picture credit: Peterson lab)

The diving birds then are only the tail end, the last participants in this elaborate system.

Ocean migrants, from birds and whales returning from the southern hemisphere to anadromous salmon and sturgeon born hundreds of miles inland, time their journeys to intercept this five month feast of copepods and higher trophic fish.

One major reason posited for this year's record low in adult Sacramento Chinook returns, and the subsequent salmon fishing ban set in place this last summer, was the failed upwelling off the coast of Southern Oregon in 2005. How could a seasonal phenomenon—500 miles north and three years in the past—stop these ancestrally freshwater fish from returning to their 2 million-year-old spawning grounds on the Sacramento River?

Jen’s boss, Bill Peterson, a plankton biologist with NOAA, is the leading researcher on the relationship between salmon returns and upwelling cycles. All species and stocks of Pacific salmon are anadromous, allowing the fish to exploit the greater abundance of food in the ocean and ease competition for spawning grounds by colonizing every spatial and temporal freshwater spawning niche. The evolutionary choice to be anadromous make the fishes’ transition from freshwater to saline habitat a crucial and tenuous stage in salmon life history.

Abundant northern copepod species (above) during upwelling have been linked to healthy salmon populations. (Peterson lab)

Until they arrive at the ocean, salmon are dark, three to five inches long, live in freshwater, feed on small crustaceans and insect larvae, and swim individually. In the salty, deep ocean, the fish are different beasts. Within the first month of their arrival in the ocean, salmon swell in size to an average of a foot apiece, turn shimmering silver, begin to school together and change their diet to anything smaller than themselves. To make this transition well and ensure survival for the next seven years before they return to spawn, the fish must eat. This is why the timing of the early stages of each species' and region’s salmon lifecycle—most of their freshwater existence—evolved around partaking in the seafood buffet of upwelling.

For the last thirty years, Peterson has been running biweekly data-gathering trips to help him map the matrix of connections between upwelling strength and salmon returns.

Jen was a member of the crew on one of these recent data gathering trips, aboard the MS Elakha. The deck of the boat is filled with post-docs, lab techs and undergraduate interns who rush about gathering samples. Two post-docs are lowering the lab robot, CTV, to get salinity, temperature and dissolved carbon dioxide and oxygen content readings at different depths. An undergraduate intern prepares bottles to gather low oxygen water samples from four hundred to a thousand feet. Jen goes into the ship cabin, where she dehydrates a liter of surface water with a vacuum pump to isolate its chlorophyll content onto a one inch thick, three-inch round filter.

In the matrix that Peterson built with his thirty years of data, he sees the failed upwelling of 2005 as the cause of this year’s fishery failure and subsequent fishing ban. For the last few years, the annual upwelling buffet has been out of synch with the salmon's transition from freshwater to marine environs. According to his data, ocean temperatures from 2002-2005 had been warmer and the larger current systems, like the Pacific Decadal Oscillation (PDO), were pulling water from the south. The weak 2005 upwelling contained a higher number of lean, southern species rather than fat, northern species. In addition, it came three months late, reducing the survival rate of salmon smolt that arrived on the coast between April and July.

The particular numbers in the matrix explain this year’s low adult returns, but what do the numbers mean for salmon populations in the long run? Were the three warm, southern copepod specie-filled upwellings between 2002 and 2005 a one-time event? Or signs of a shift in upwelling regimes from ten year PDOs to four-year PDOs?

Peterson doesn’t think this is a one off, weird decade of events. He sees a pattern of warmer currents moving north and species following the shift north accordingly. He already identifies a change in PDO cycles from ten years to four years. The question is, can salmon adapt fast enough to the new change in upwelling cycles?

Further reading