Evidence gleaned from the instrumental record of climate data identifies a robust, recurring pattern of ocean-atmosphere climate variability centered over the midlatitude North Pacific basin. Over the past century, the amplitude of this climate pattern has varied irregularly at interannual-to-interdecadal timescales. There is evidence of reversals in the prevailing polarity of the oscillation occurring around 1925, 1947, and 1977; the last two reversals correspond to 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.

A principal component analysis reveals that Pacific salmon catches in Alaska have varied inversely with catches from the U.S. West Coast during the past 70 years. If variations in catch reflect variations in salmon production, then results of our analysis suggest that the spatial and temporal characteristics of this “inverse” catch/production pattern are related to climate forcing associated with the Pacific Decadal Oscillation, a recurring pattern of pan‐Pacific atmosphere‐ocean variability. Temporally, both the physical and biological variability are best characterized as alternating 20‐to 30‐year‐long regimes punctuated by abrupt reversals. From 1977 to the early 1990s, ocean conditions have generally favored Alaska stocks and disfavored West Coast stocks. Unfavorable ocean conditions are likely confounding recent management efforts focused on increasing West Coast Pacific salmon production. Recovery of at‐risk (threatened and endangered) stocks may await the next reversal of the Pacific Decadal Oscillation. Managers should continue to limit harvests, improve hatchery practices, and restore freshwater and estuarine habitats to protect these populations during periods of poor ocean productivity.

A major reorganization of the North‐east Pacific biota transpired following a climatic `regime shift' in the mid 1970s. In this paper, we characterize the effects of interdecadal climate forcing on the oceanic ecosystems of the NE Pacific Ocean. We consider the concept of scale in terms of both time and space within the North Pacific ecosystem and develop a conceptual model to illustrate how climate variability is linked to ecosystem change. Next we describe a number of recent studies relating climate to marine ecosystem dynamics in the NE Pacific Ocean. These studies have focused on most major components of marine ecosystems – primary and secondary producers, forage species, and several levels of predators. They have been undertaken at different time and space scales. However, taken together, they reveal a more coherent picture of how decadal‐scale climate forcing may affect the large oceanic ecosystems of the NE Pacific. Finally, we synthesize the insight gained from interpreting these studies. Several general conclusions can be drawn. 1 There are large‐scale, low‐frequency, and sometimes very rapid changes in the distribution of atmospheric pressure over the North Pacific which are, in turn, reflected in ocean properties and circulation. 2 Oceanic ecosystems respond on similar time and space scales to variations in physical conditions. 3 Linkages between the atmosphere/ocean physics and biological responses are often different across time and space scales. 4 While the cases presented here demonstrate oceanic ecosystem response to climate forcing, they provide only hints of the mechanisms of interaction. 5 A model whereby ecosystem response to specified climate variation can be successfully predicted will be difficult to achieve because of scale mismatches and nonlinearities in the atmosphere–ocean–biosphere system.

There are two fundamental ways of doing science: the experimental‐predictive and the historical‐descriptive. The experimental‐predictive approach uses the techniques of controlled experiment, the reduction of natural complexity to a minimal set of general causes, and presupposes that all times can be treated alike and adequately simulated in the laboratory. The historical‐descriptive approach uses a mode of analysis which is rooted in the comparative and observational richness of our data, is holistic in its treatment of systems and events, and assumes that the final result being studied is unique, i.e. dependent or contingent upon everything that came before. We suggest that one of the real difficulties we have in understanding ecosystem properties is our inability to deal with scale, and we show how historical science allows us to approach the issue of scale through the interpretation of pattern in time and space. We then use the techniques of the historical‐descriptive approach to doing science in the context of our own and other research on climate change and biological production in the North‐east Pacific Ocean. In particular, we examine rapid decadal‐scale shifts in the abundance and distribution of two major components–salmon and zooplankton ‐ of the large marine ecosystem of the North‐east Pacific, and how they relate to similar shifts in North Pacific atmosphere and ocean climate. We conclude that they are all related, and that climate‐driven regime shifts, such as those we have identified in the North‐east Pacific, can cause major reorganizations of ecological relationships over vast oceanic regions.

To better understand and predict Oregon coho (Oncorhynchus kisutch) marine survival, we developed a conceptual model of processes occurring during four sequential periods: (1) winter climate prior to smolt migration from freshwater to ocean, (2) spring transition from winter downwelling to spring/summer upwelling, (3) the spring upwelling season and (4) winter ocean conditions near the end of the maturing coho's first year at sea. We then parameterized a General Additive Model (GAM) with Oregon Production Index (OPI) coho smolt‐to‐adult survival estimates from 1970 to 2001 and environmental data representing processes occurring during each period (presmolt winter SST, spring transition date, spring sea level, and post‐smolt winter SST). The model explained a high and significant proportion of the variation in coho survival (R2 = 0.75). The model forecast of 2002 adult survival rate ranged from 4 to 8%. Our forecast was higher than predictions based on the return of precocious males (‘jacks’), and it won't be known until fall 2002 which forecast is most accurate. An advantage to our environmentally based predictive model is the potential for linkages with predictive climate models, which might allow for forecasts more than 1 year in advance. Relationships between the environmental variables in the GAM and others (such as the North Pacific Index and water column stratification) provided insight into the processes driving production in the Pacific Northwest coastal ocean. Thus, coho may be a bellwether for the coastal environment and models such as ours may apply to populations of other species in this habitat.