Climate Variations and Ecosystem Regime Shifts in the North Pacific

Analyses of climate, ecosystem survey, and fishery data collected over the past century have identified evidence for climate-driven changes in many North Pacific marine resources that have persisted for one or more decades. For much of the 20th century a clear north-south inverse production pattern for Pacific salmon had a time dynamic that closely followed that of the Pacific Decadal Oscillation (PDO), which is the dominant pattern of North Pacific sea surface tempera­ture variability. Variability in the PDO pattern exists at all time scales, but can be explained as the result of “red noise” processes that yield increased variance at lower frequencies. In the 20^th century, total Alaska salmon production was high during warm regimes of the PDO but relatively low during cool regimes of the PDO. In contrast, salmon production off the west coast of California, Oregon, Washington, and southern British Columbia tended to be especially low during warm phases of the PDO, and especially high during cool phases. The warm era of the PDO that prevailed from 1977-1998 also marked an era with large reductions in the abundance of Alaska’s crab, shrimp, and small forage fish, but large increases in the biomass of flatfish, cod and pollock in the Bering Sea and Gulf of Alaska. Rapid and dramatic changes in marine ecosystem community structure like those observed in the North Pacific and Bering Sea have been termed ecosystem regime shifts. Predictability for the kind of persistent climate variations thought to trigger North Pacific ecosystem regime shifts appears to be highly limited, which in turn suggests that there is little predictability for ecosystem regimes shifts.  Recent research has also shown that, at finer scales of aggregation, ecological responses may not be well correlated with broader, regional-scale ecological responses to the same large-scale climate forcings. The existence of natural and persistent change in north Pacific marine ecosystems and the living marine resources they support, plus locally complex ecological responses to climate forcing, highlight the need for resource use and management strategies that are resilient in the face of volatile resource availability.