Regime shifts in the North Pacific: early indications of the 1976–1977 event

A major environmental change, since dubbed a “regime shift”, occurred in the North Pacific in 1976–1977. However, it was not identified as such until the early 1990s. Recognition was complicated by the presence of higher frequency, interannual variations in both the physical and biological time series. In retrospect some symptoms of the event were apparent within a few years of the shift. These included changes in SST distribution and zooplankton abundance as well as in the recruitment, abundance, and distribution of commercial fishes. Such observations, while not diagnostic at the time, are consistent with the larger scale analyses of recent years.Of particular interest was the demonstrated impact on commercial fish stocks, indicating that early recognition of such events could be useful for fishery management. There is some evidence that appropriate ecosystem data, by integrating the higher frequency variations, when combined with physical data might have advantages for early detection of major environmental changes. While fishery data can clearly indicate that change has occurred, their utility for this purpose is often limited because of inadequate sampling, length of fish life cycles, the complicating effects of fishing and delays in processing of the data. Selected zooplankton species might be the most useful early indicators of environmental change if sampling coverage could be increased and speedy means of identification developed.