Evidence gleaned from the instrumental record of climate data identifies a robust, recurring pattern of ocean-atmosphere climate variability centered over the mid-latitude Pacific basin. Over the past century, the amplitude of this climate pattern has varied irregularly at interannual-to-interdecadal time scales. There is evidence of reversals in the prevailing polarity of the oscillation occurring around 1925, 1947, and 1977; the last two reversals correspond with dramatic shifts in salmon production regimes in the North Pacific Ocean. This climate pattern also affects coastal sea and continental surface air temperatures, as well as streamflow in major west coast river systems, from Alaska to California.
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Links to related articles:
Climate and Extinction Risk for Salmon Populations of the Northeast Pacific
Inverse production regimes: Alaskan and West Coast Pacific Salmon
A nice web-article titled Long-term Climate Trends and Salmon Populations, by George Taylor (Oregon State Climatologist), is here.