Climate Variation, Regime Shifts, and Implications for Sustainable Fisheries

The term ecosystem regime shift refers to low frequency, high amplitude variation in marine ecosystems involving changes in community composition, species abundances, and trophic structure. Changes occur in the abundance of both exploited and unexploited populations. Temporally coherent changes often occur in other spatially separated ecosystems. Ecosystem regime shifts are thought to be a response to shifts in the ocean and atmosphere climate and hence are relatively coherent with climate changes. However, the mechanisms responsible for ecosystem regime shifts are not well established. Changes in energy flow from the base of the ecosystem is frequently thought to be responsible, but in some cases climate-induced changes in apex predators also result in top-down responses. For example, regime shifts appeared to have occurred in the North Pacific in 1977 and 1989.