World-wide fluctuations of sardine and anchovy stocks: the regime problem

Summed differences between the highest and lowest catches of two clupeoid taxa, sardines Sardinops spp. and Sardina pilchardus and anchovies Engraulis spp., in five regions where they co-occur are in excess of 29 million tons. Both taxa show large expansions and contractions of range with changes in abundance. Populations of sardines also shift alongshore, possibly in response to climate change. At time-scales of several decades, fluctuations in catches of sardines and anchovies are seemingly dominated by long-term environmental variations which cause large and prolonged changes in abundance and give rise to "regimes" of sardine or anchovy. These long-term fluctuations are probably associated with persistent environmental changes of oceanic to global scale, there being coherence of trends in various sardine stocks on an oceanic scale and similarities between these changes and global, hemispheric and oceanic indices of the environment.