Thursday, February 16, 2012

Ocean Conditions Primed for Excellent 2012 Survival

While a multitude of factors in freshwater may drive long term trends in salmon populations, year to year variation in abundance is typically the result of the conditions in the marine environment. The survival of smolts in the early marine environment is highly variable and is known to have a particularly important role in determining the size of the subsequent adult run. In the area around the mouth of the Columbia River researchers monitor yearly changes in the productivity of the ocean food web and their effects on the survival and growth of juvenile salmon.

In this region productivity is largely driven by summer upwelling whereby summer winds transport surface waters offshore bringing cold, nutrient rich bottom water to the surface to replace it. Years of strong upwelling are often associated with La Niña conditions and negative (cold) phases in an oceanographic phenomenon called Pacific Decadal Oscillation (PDO). Typically, the survival of juvenile salmon outmigrating from the Columbia tracks closely with these environmental indicators and many of the best years for Columbia River salmon and steelhead have come on the heels of outmigration years with strongly negative PDO and La Niña conditions.

Now after two consecutive La Niña years and with PDO locked in a strong negative phase, scientists with NOAA fisheries say we're primed to have some of the best out migration conditions in recent memory. Years like these are a major boon to populations of wild salmon and steelhead in the Columbia Basin; excellent survival in 1999-2000 and again in 2007-2009 which helped turn the tide against extinction for many populations was largely due to good ocean conditions and court mandated spill in the later years.

More information in the Northwest Fish Letter:

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