Revisiting the Regime Problem hypothesis: 25 years later

Abstract

Small pelagic fish species have been a central research topic for more than 60 years because of their ecological role, their economic importance, and the apparent multidecadal large fluctuations in catches, synchronic fluctuations from remote regions, and the alternation between the abundance of sardine and anchovies within each system. Strong evidence supports the observation that low-frequency fluctuations of small pelagics occur naturally. However, the synchrony and the alternation have been questioned. In this study, the Regime Problem hypothesis is revisited by updating the fish catch time series to 2015, and by incorporating into the analyses stocks not originally considered due to the time series lengths. The specific questions addressed here are: 1) whether the synchronic fluctuations of small pelagics catches from remote regions and the species alternation between species within each system, observed for the last century in the Regime Problem literature, remains after updating the time series, and 2) If a multidecadal signal can also be detected in regions that were not considered in the original Regime hypothesis framework. Results indicate that the multidecadal synchrony between systems and alternation between species remains clear for the Kuroshio and Humboldt systems. The California small pelagics cannot be considered to be in phase with the other systems, that in Benguela alternation is not evident during at least the last two decades, and that there is not a single worldwide mode of variability teleconnecting all small pelagics.