Salmon Survival: It's All About
2010 Tough to Call
Ocean conditions off the coast of Oregon and Washington changed from nightmarish to dreamy for juvenile salmon this past late spring-early summer and in the process confounded experts' efforts to predict how those young fish may have fared.
"The fact that ocean conditions were poor early in the season but great later in summer makes it impossible to provide any reliable forecast this year: our best 'guess' is that we can expect near 'average' returns in 2011 (for coho) and 2012 (for chinook)," according to the Northwest Fisheries Science Center's annual qualitative prediction of future returns. "We do not think that the El Nino had a devastating effect on salmon because the warm ocean conditions at the time of ocean entry (in April/May) were about 'average.'"
NOAA Fisheries' NWFSC has over the past 13 years developed a suite of ocean ecosystem "indicators" that are monitored and the data then used to estimate what kind of an impact they might have had on juvenile salmon during the earliest stage of their ocean sojourn. Basically, the better the survival early on, the more fish are expected to survive to adulthood to return to the Columbia River basin to spawn.
Each of the 18 or so indicators is rated for the year as good, neutral or bad. Then they are compared individually to past measurements and, as was the case this year, given a score of from 1 (the best combined score over the course of the study) to 13 (the worst).
The run-size forecasts are based on the average score for the indicators overall.
The mean of those scores for 2010 ranked the year eighth out of 13, which would indicate slightly below average overall conditions for coho and spring chinook salmon that ventured to sea last spring. The forecasts are for the first year that species' begin to return as fully matured adults, in the coho's case after one year in the Pacific and the spring chinook after two years.
"There's some hints that it was not that terrible" for young fish that typically would have entered the ocean before conditions turned from bad to good, said Bill Peterson, NOAA Fisheries oceanographer and senior scientist. The number of coho jacks that returned, as counted at Bonneville Dam, after just a few months in the ocean was in the average range, he said. The strength of a jack return can mirror the strength of broodmate returns in succeeding years.
In the California current that hugs the coast, and elsewhere, cold is good for salmon.
"Because of the 2009-10 El Nino event, the ocean began to warm in autumn 2009 and remained warm through April 2010, after which a cooling trend resumed in May 2010," the forecast says. The El Nino/Southern Oscillation is the measure of sea surface temperatures in the equatorial Pacific that can affect climate worldwide.
"Thus, 2010 began as a 'warm year,' began to cool in May but by July, the ocean was the coldest observed in recent years. Thus we had very mixed signals in 2010 making it difficult to offer any reliable outlooks in returns of coho salmon in 2010 and chinook salmon in 2012," the forecast says.
"During the tail end of the El Nino, in May and June, we had some of the worst ocean conditions we've seen in the 13 years we've been sampling," Peterson said. "Then in July, the conditions were as good as they've ever been. So it's a question of timing" and what the fish did once they entered the ocean.
Coho tend to hang out not too far off the coast and not too deep. The spring chinook don't seem to dawdle too long before charging north up the continental shelf to parts unknown.
At the time of the young fishes entry, "the ocean really was kind two-layered" with warm surface water and cool water deeper that was relatively plentiful in terms of nutrients on which juvenile salmon feed.
Survival may have depended on "if they had enough sense to go deeper," Peterson said. Coho and steelhead have a more shallow orientation than chinook.
"Vertical structure is really something we've really not thought about," Peterson said.
For the past 13 years, Peterson and his colleagues have conducting trawl surveys funded by the Bonneville Power Administration in June and September from Cape Perpetua to La Push, Wash., counting the abundance of juvenile salmon along the near-shore waters of the West Coast. The survival rate of juvenile salmon is the key indicator for future salmon runs, says Peterson.
When salmon first enter the ocean, they must have enough food to not only survive, but to grow rapidly enough to avoid predation. The smaller they are, the more vulnerable they are to potential predators lurking offshore. And when ocean productivity is high, populations of other fish like herring, anchovies and sardines grow and provide alternatives for the predators.
Peterson said the juvenile chinook counted this summer was the fifth highest they've had in their 13 years, raising hope for future chinook runs. But the season's mixed bag continued
"We caught almost no juvenile coho salmon in September and that worries me," Peterson said.
"We'll find out soon enough," he said. "Coho return as adults after 18 months; spring chinook come back after two years and fall chinook, three years or longer. If these fish can make it to adulthood, they should be fine. There's not much that out there that feeds on them other than sea lions and orcas.
"It's all about how they fare as youngsters," he added, "and the jury is definitely still out this year."
If the cool La Nina and negative Pacific Decadal Oscillation keep their grip, conditions should be much improved by the time this year's class ventures out.
SST anomalies were consistently colder than normal by several degrees during the summer of 2010 and the deep water temperatures on the continental shelf in July-August were the coldest of the 13-year record.
And the biomass of the lipid-rich "northern" copepod species was the third highest on record during the summer of 2010. The northern copepods are a key link in the food chain.
The negative signals dominated early in the spring-summer season. The PDO was positive (generally considered bad for salmon) and SSTs were warm during the winter of 2009-2010 indicating poor ocean conditions during the winter.
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 information posted on NWFSC's "Ocean Ecosystem Indicators of Salmon Marine Survival in the Northern California Current" web site. That site is located at: http://www.nwfsc.noaa.gov/research/divisions/fed/oeip/a-ecinhome.cfm
The index is also correlated with salmon landings from Alaska, Washington, Oregon and California.
"Although the winter storms ended in late March and the upwelling season was initiated on 5 April, strong upwelling was not initiated until two months later, on 9 June," according to the forecast. The length and strength of the upwelling is indicative of the availability of fish food delivered to the surface.
"Within that two months period several southwest storms moved through the region. This is generally a negative sign for salmon that enter the ocean in April-May," the forecast says.
"Copepod species richness was very high during winter-spring-summer of 2010, ranking 11 of 13 from May-September. We regard this as a negative sign because it indicates that the sub-tropical species that were brought to Oregon with the El Nino persisted for several months after the end of the El Nino event; species richness did not return to normal until autumn 2010."
learn more on topics covered in the film
see the video
read the script
learn the songs