Have there been recent changes in climate? Ask the fish

It is generally accepted that a climate shift occurred about 1977 that affe cted the dynamics of North Pacific marine ecosystems. Agreement on the poss ibility of further climate shifts in 1989 and the late 1990s is yet to be a chieved. However, there have been changes in the dynamics of key commercial fishes that indicate changes in their environment occurred in the early 19 90s, and possibly around 1998. One method of measuring climate change is to observe the dynamics of species that could be affected. Several studies have described decadal-scale changes in North Pacific clima te-ocean conditions. Generally, these studies focus on a single index. Usin g principal components analysis, we use a composite index based on three as pects of climate ocean conditions: the Aleutian Low Pressure Index, the Pac ific Atmospheric Circulation Index and the Pacific Interdecadal Oscillation Index. We link this composite index (Atmospheric Forcing Index) to decadal -scale changes in British Columbia salmon and other fish populations. Aroun d 1989 there was a change from intense Aleutian Lows (above average south-w esterly and westerly circulation patterns and warming of coastal sea surfac e temperatures) to average Aleutian Lows (less frequent south-westerly and westerly circulation and slightly cooler coastal sea surface temperatures i n winter). These climate-ocean changes were associated with changes in the abundance and ocean survival of salmon (Oncorhynchus spp.), distribution an d spawning behaviour of hake (Merluccius productus) and sardines (Sardinops sagax) and in recruitment patterns of several groundfish species. (C) 2000 Elsevier Science Ltd. All rights reserved.