NOAA Research Linking Sea Temperature Swings to Salmon Return Numbers 

Columbia Basin Bulletin

March 7, 2008  

North Pacific sea surface temperatures have historically swung up and down in 20 to 30-year cycles, changing with it climatic and ecological variables that shift the fate of salmon.

That cold-warm-cold-warm pattern has quickened over the past 10 years -- exhibiting turnarounds that have lasted only four years, according to research being conducted by the NOAA Fisheries Service's Northwest Fisheries Science Center .

The good news is that this sea surface cycle, dubbed the Pacific Decadal Oscillation, last year appeared to have entered a negative, cool phase, which most often signals a rise in the number of salmon that return to the Columbia River basin in succeeding years.

The PDO, like shorter term La Nina/El Nino (ENSO) patterns, is characterized by changes in sea surface temperature, sea level pressure, and wind patterns. Past research has shown that warm eras have seen enhanced coastal ocean biological productivity in Alaska and inhibited productivity off the west coast of the contiguous United States . Cold periods reverse that north-south pattern of marine ecosystem productivity.

"The biology reacts quickly" to such changes in ocean conditions, according to Edmundo Casillas, NWFSC Ocean and Estuary program leader. "Salmon respond equally as fast."

During a Thursday presentation to the Columbia Basin 's Regional Forum Implementation Team, Casillas pointed out that at no time since 1900 had there been a deviation from an established PDO regime of longer than 16 months. Once established, warm or cool regimes have stayed locked in with an occasional brief lapse, sometimes influenced by a contrary ENSO.

Most recent history shows, however, that the North Pacific has had two shifts of four years duration recently: a cold era from 1999-2002 and warm period from 2003-2006. Chinook salmon returns to the Columbia mirrored those trends with total numbers climbing upwards from 2000-2003, then declining for the next four years.

The University of Washington scientist Nathan Mantua and colleagues were the first to show that adult salmon catches in the Northeast Pacific were correlated with the PDO.

Regardless of the duration of any ocean condition, it is important that freshwater fish managers know what is happening so they can evaluate the benefits of salmon recovery actions and respond accordingly, Casillas said. Advancing global warming could complicate things, affecting the duration and variability of the large scale climate forces.

"You need to be cognizant of what's going on in the ocean to do what you need to do in freshwater," Casillas said. In anticipation of poor ocean conditions, as an example, hatchery managers might scale back their production to reduce potential competition between hatchery and wild fish for resources that will be in short supply.

The NWRFC has for the past 10 years been monitoring a variety of physical and biological ocean conditions that may affect the growth and survival of juvenile salmon in the northern California current off Oregon and Washington. The 30-40 mile swath of ocean represents the young fishes' first saltwater experience after they leave the Columbia River estuary.

"That's when they're smallest and most vulnerable" to predators and other natural forces, and when the recruitment into future adult returns can most be affected, Casillas said.

Those physical, biological and ecosystem "indicators" have for the past few years been fed into a forecasting tool that documents current ocean conditions and potential impact on salmon survival 1 to 2 years ahead of their actual return. The NWFSC monitoring and forecasting focuses on that first year at sea through food-chain processes.

The most recent forecast, released late last month, says that the PDO tide has turned, shifting last year to a neutral, and then a negative, cool phase. Environmental changes seemed to follow.

"What we're seeing is the ocean is improving," said Casillas. The latest "Ocean Ecosystem Indicators of Salmon Marine Survival in the Northern California Current " forecast's indicators, cumulatively, fall in the positive (for fish) mid-range.

"Most indicators in 2007 pointed toward greatly improved ocean conditions compared to the previous few years. Indicators that point to good salmon survival included a cold ocean in winter/spring 2007, an early spring transition date, high biomass of cold--water lipid--rich copepods, and a long upwelling season." according to the updated NWFSC adult spring chinook and coho forecast. "Negative indicators included weak upwelling in late spring and summer, very warm sea surface temperatures, and low catches of juvenile coho in September surveys."

Fish sampling last year also showed a good news-bad news result. In June 2007, trawl surveys collected the third highest number of juvenile spring chinook in the 10 years of sampling. That suggests "improved adult spring chinook runs can be expected in 2009," according to the forecast, when the first adults from that year class return to the Columbia .

Catches of juvenile coho in September produced some of the lowest catches of juvenile coho (7th worse in 10 years of surveys).

"Since it is widely believed that juvenile coho live only within the upper few meters of the water column, we hypothesize that the anomalously warm waters, in some way, led to the demise of the juvenile coho.

"They either moved (out of the sampling area) or they died. We think they died," Casillas said. The trawl surveys follow eight transect lines running from Newport , Ore. , north to La Push, Wash.

The forecast calls for a poor coho return, though improved numbers for coho that went to sea in 2007 and return in 2008. The relatively early transition of the zooplankton community in spring, and the high biomass of coldwater zooplankton species could counter to some extent coho trawl catch statistics.

Ocean conditions at the time of the spring chinook's ocean entry were "very good" last year.

"Since spring chinook juveniles reside in waters off Oregon and Washington for only a few weeks before migrating north to unknown waters, their survival might have been relatively well supported by these conditions. These fish could begin to return as early as spring 2009," the forecast says.

Adult return data displayed as part of the forecast show that the 4-year period of cold ocean conditions (1999-2002) resulted in good returns of chinook salmon. Warm ocean conditions from 2003 to 2006 correspond with declining returns.

"We expect at least one more year of poor returns from this period, after which returns should begin to increase, so long as the cold ocean conditions observed in 2007 continue into 2008 and beyond," the forecast says.

The forecast charts an "improving set of conditions" that began later in 2006, Casillas said. The numerous variables monitored came out, on average overall, in the mid-range for fish that emerged from the Columbia in 2006, thus anticipated an improved spring chinook return this year.

Federal, state and tribal fishery officials have forecast a strong upriver spring chinook return this year. That prediction was based in large part on a near-record return of "jacks," fish that returned after only one year in the ocean.

The forecast can be found at:

http://www.nwfsc.noaa.gov/research/divisions/fed/oeip/a-ecinhome.cfm

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