The re-occurrence of sardines off British Columbia characterises the dynamic nature of regimes

Sardine (Sardinops sagax) fisheries were the largest in British Columbia from the mid-1920s to the mid-1940s, and catches averaged 40,000t annually. In 1947 not only did the fishery off British Columbia collapse but also the sardines disappeared totally from British Columbia waters. Sardines re-appeared in 1992, after a period of 45 years. As their abundance increased, sardines spawned off the west coast of British Columbia in 1997 and 1998, and one year old juveniles became distributed along the entire coast and off the coast of Alaska. This distribution and spawning behaviour was not reported in the 1930s and 1940s. The changes in sardine dynamics were related to regime shifts, but did not oscillate in synchrony with all the decadal-scale changes in climate as indexed by the pattern of the Atmospheric Forcing Index (AFI). This response indicates that the linkage between sardines and climate regimes is specific to an assemblage of factors that characterise the regimes. Indicators of ecosystem change such as temperature should be viewed more as surrogates of change than specific regulators of distribution and abundance. The specific aggregate of factors that create favourable ecosystems for sardines remains to be discovered. We suggest that it is the change of regimes that creates conditions favourable to sardines by improving the productivity of diatoms that are specific to the improved early survival of larval sardines.