NOAA's New Fish Predictions:
by Bill Rudolph
Scientists from NOAA Fisheries' Seattle science center are predicting that 199,000 spring Chinook will return to Bonneville Dam this year, but poor conditions for juveniles migrating north off the coast this spring could mean the 2016 return may be about 25 percent lower than the projected 2015 run, but close to the current 10-year average of 158,000.
The feds also estimated that 530,000 fall Chinook salmon will return to Bonneville Dam and that coho salmon in the region will be surviving at a 2.23-percent rate. For 2016, they don't expect more than 383,000 fall Chinook past Bonneville, which would put it a little below the 10-year average of 423,000 fish.
Columbia Basin harvest managers, using their jack-based methodology, are calling for about 30,000 more springers than the feds' estimate, along with fall Chinook returns that may rival last year's nearly million fish return.
The NOAA Fisheries' predictions were fine-tuned compared to previous years, the scientists say, by placing more weight on indicators that correlate better with returns. For instance, when large numbers of northern copepods are around when the young fish are migrating, adult returns are usually higher. The northern copepods provide a more nourishing food source for pelagic fish than those from southern, warmer waters that are, in turn, preyed on by young salmon.
When the Pacific Decadal Oscillation index is negative, and northerly winds have led to relatively cool near ocean temperatures, the biomass of northern copepods is usually high, but low for southern copepods. The ratio between the two types of zooplankton can vary by an order of magnitude (10 times)--southern species of copepods show up more when winds are lighter and more southerly.
But other indicators associated with ocean upwelling, like spring transition date (when winds switch from southerly to northerly), upwelling anomalies, and the length of the upwelling season, were removed from NOAA's "Stoplight" chart that looks at different factors qualitatively. The scientists said the upwelling indicators explained only 14 percent of the ecosystem variability over the years, while other factors more than 50 percent.
NOAA scientist Bill Peterson said it's still uncertain how much of a role the annual upwelling events really play in the survival of young Columbia River salmon, but so far, with 17 years of data under their belts, he said it doesn't seem like much.
In 2014, Peterson said, fewer of the northern, more nourishing types of copepods were evident off the coast, which was to be expected, since waters were warming to El Nino-like levels, even though a real El Nino has not yet developed. The culprit is a "warm blob" of water that was concentrated in the Gulf of Alaska most of the year and has moved easterly toward the West Coast as it slowly dissipates.
"Many of the ecosystem indicators for 2014 point toward this being a relatively poor year for salmon survival," said the latest report from NOAA. The scientists said the summer PDO values were strongly positive (warm), coinciding with that 'warm blob' in the Gulf of Alaska. Though El Nino conditions were officially neutral, sea surface temperatures were warmer than normal, and the upwelling season, which brings cooler more nutritious water to the surface, started late and ended early.
There is still a high abundance of large, lipid-rich zooplankton around, but low numbers of winter fish larvae that grow into salmon prey by spring. The June 2014 trawl surveys off Washington and Oregon produced only moderate catches of juvenile spring Chinook, ranking only ninth highest in the past 17 years, quite a switch from the 2013 survey, which ranked second.
Peterson said his group is still working on incorporating other factors in their analysis, such as annual productivity in the Gulf of Alaska, but there is little data being collected annually. He noted that in 2013, the Columbia River spring Chinook return came in about half what their indicators had predicted. Later, an analysis of satellite data showed extremely low chlorophyll levels in the Gulf of Alaska in 2011, when the juvenile fish migrated north.
The NOAA scientists said their best guess is to expect average returns of coho in 2015 and Chinook in 2016, but added that "similar to the statement we made last year, the mixed signals add greater uncertainty to our predictions."
Ocean 'Indicators' Help Forecasts for Salmon Returns by Staff, Columbia Basin Bulletin, 3/20/9
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