Climatic and accompanying ocean conditions that have remained “persistently negative,” since late spring/early summer 2010, could bode well for Columbia River basin and other salmon populations that return from the Pacific to spawn next year, the year after, and possibly beyond.
“I think we’re going to have a heck of a year” if current climatic conditions persist into the spring when young salmon and steelhead exit the Columbia River to rear for a year or two or more in saltwater, said Bill Peterson, NOAA Fisheries senior scientist and oceanographer.
In the case of young salmon that enter the ocean each spring and summer in search of food to grow, and survive, negative Pacific Decadal Oscillation conditions in the ocean are good. They generally bring cooler water offshore, stronger upwelling of nutrients that bolster the food chain and bring the presence of more fat-rich northern copepod, which fortify populations of small fish on which salmon feed.
The PDO is a climate index based upon patterns of variation in sea surface temperature of the North Pacific from 1900 to the present. While derived from sea surface temperature data, the PDO index is well correlated with many records of North Pacific and Pacific Northwest climate and ecology, including sea level pressure, winter land-surface temperature and precipitation, and stream flow, according to NOAA Fisheries.
The index is also correlated with salmon landings from Alaska, Washington, Oregon, and California. Negative or cold PDO cycles have most often witnessed better ocean survival and stronger spawner returns.
“Strong negative values of the PDO were observed in autumn 2011; if these values persist through winter and early spring 2011-2012, they could result in the best ocean conditions observed in decades,” according the 2011 annual update for the “Ocean Ecosystem Indicators of Salmon Marine Survival in the Northern California Current” research project, which has been ongoing since 1998.
The report and other materials about the research can be found at:
For the project, NOAA Fisheries Service Northwest Fishery Science Center scientists have monitored a suite of physical, biological and ecological “indicators” of ocean conditions in an attempt to determine how young salmon from the Columbia River might fare during their first few months in the Pacific. While the average of those indicators last year was about average (eighth out of 14 years of study), things are looking good right now.
“This is the first indication that 2012 could result in some of the highest returns of Columbia River coho salmon in 2013 and spring chinook in 2014,” the 2011 annual report says of the continuing negative phase PDO.
In addition, cold (negative) sea surface conditions and other factors that continue in the equatorial Pacific have created La Nina conditions.
“These negative values are expected to continue into spring 2012, which suggests that the northern North Pacific Ocean will also remain cold through spring 2012, giving rise to continuation of good ocean conditions,” the summary says.
“Salmon like cold water,” Peterson said. Conditions that exist in the California Current along the West Coast now tend to sweep down those northern copepods, which better fuel the food chain than their southern counterparts.
“Northern copepod biomass in 2011 has been the highest in recent years, indicating improved ocean conditions compared to the past few years. This suggests good feeding conditions for the baitfish upon which juvenile salmon feed,” the summary says.
“It also means stronger upwelling” of nutrients from the ocean’s depths, Peterson said.
Catches of coho in the September 2011 survey were relatively high, ranking 5th overall among 14 annual surveys. The scientists conduct trawl surveys off the coast for chinook in June and coho in September to evaluate those two indicators of survival during the fishes’ first few months in the Pacific.
The NWFSC scientists have a seen strong correlation between highly ranked years (favorable indicators) and strong coho and spring chinook adult returns a year and two years later, respectively. In 2008, as an example, the average rank (each indicator is ranked poor, good or average) was the best in a 12-year data set. The return of coho in 2009 was the fifth highest since 1970; and the upriver spring chinook the following year was the third best since at least 1980.
The look ahead at 2012 noted a few not-so-encouraging signals as well as regards to fish.
-- Upwelling from April through early June 2011 was relatively weak. Another negative indicator is that upwelling ceased very early, in mid-September.
-- Deep water on the continental shelf was among the warmest in the study’s 16-year time series, indicating weak upwelling in 2011.
--Throughout 2011 the scientists found low copepod species richness values, an indication of improving ocean conditions; however, the low anomalies were less negative than in other “good” years.
-- Ichthyoplankton biomass in January-March 2011 (winter) was among the lowest values in the time series, indicating poor feeding conditions for salmon that entered the sea in spring 2011.
-- Catches of juvenile spring chinook in the June surveys were poor, ranking 10th of 14 years.
“… similar to the past two years, individual indicators have sent a mixed message [in 2011]. Certain indicators suggest the potential for above average returns: persistence of strong La Niña conditions, a negative PDO, positive copepod anomalies from May-September, and reasonably high catches of coho in the September survey,” the 2011 report summary says.
“However, negative indicators include relatively warm surface and deep waters on the continental shelf, weak upwelling in spring, a short upwelling season, and low abundances of ichthyoplankton during January-March. Because of these mixed signals, we are less certain of our prediction for coho in 2012 and Chinook in 2013.”
Our best guess is to expect average to above-average returns of coho in 2012 and chinook in 2013,” the study’s most recent adult return forecast says. “Based on a simple comparison to adult counts at Bonneville, this translates to 170,000 spring chinook, 110,000 coho and 400,000 fall chinook.
“Perhaps the most positive sign is that the ocean became very cold (and the PDO signal strongly negative) in summer 2010 and has remained so today. If the cold conditions continue to persist in 2012, we may be seeing some of the better ocean conditions among the past 15 years.”