Climate Variability & Marine Fisheries
Salmon Populations from Alaska Increased at the Same Time Salmon Stocks From California,
Oregon, and Washington Declined
Salmon stocks from Alaska have been highly productive since the 1976 regime change in the North Pacific, an estimated 3 times more productive than in the 1946-75 period. The periods of increased salmon production correspond to an eastward shift of the Aleutian Low pressure system which produces more frequent and severe winter storms, and a warming of the surface waters in the Gulf of Alaska. This shift between warm and cold periods is now called the Pacific Decadal Oscillation or PDO. The warmer conditions and increased nutrient levels from upwelling in the central Alaska gyre carried northward toward the coast may have contributed to the observed increase in plankton, a source of food for young salmon in the ocean, and thereby to increased Alaskan salmon production. The exact mechanisms that enhanced production are still being investigated, but the change in Alaskan salmon production in the two regimes is well documented. Salmon stocks from California, Oregon, and Washington have increased and decreased out of phase with the fluctuations in salmon in Alaska--and this "reciprocal oscillation" has been going on for the 70 years of available records.
Some of the present severe declines have been attributed to changes in their fresh water habitat, including loss of stream habitat, problems resulting from hydroelectic dams, and overharvesting. Environmental signals corresponding to the climate change since 1976 include decreased precipitation and streamflows and warmer coastal ocean temperatures. Sustained cool surface temperatures near the coast, indicating upwelling of nutrient rich water, during the period when young salmon enter the oceans are related to good salmon survival. So warm conditions in this period usually result in poorer survival.
(For current research on the relationship of ocean temperature to Oregon coho survival, go to: PFEL Salmon Research -- James Cole )
(For an Oregon perspective on the decadal variablility, go to: http://www.ocs.orst.edu/reports/climate_fish.html )
1) Beamish, R.J. and D.R. Bouillon. 1993. Pacific Salmon Production Trends in Relation To Climate. Can. J. Fish. Aquat. Sci. 50:1002-1016. 2) Hare, S.R., Mantua, N.J., and Francis, R.C. 1999. Inverse Production Regimes: Alaska and West Coast Pacific Salmon. Fisheries. 24: 6-14. 3) Mantua, N.J., S.R. Hare, Y. Zhang, J.M. Wallace, and R.C. Francis. 1997. A Pacific Interdecadal Climate Oscillation With Impacts On Salmon Production. Bull. Amer. Meteorological Soc. 78:1069-1079.