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Lluch-Cota, D.B.; Hernández-Vázquez, S.; Lluch-Cota, S.E.
Empirical investigation on the relationship between climate and small pelagic global regimes and El Niño-Southern Oscillation (ENSO).
FAO Fisheries Circular. No: 934. Rome, FAO. 1997. 48p.

El Niño-Southern Oscillation (ENSO) variability is probably the best known mechanism of global climate variability, with large effects on marine ecosystems and particularly on small pelagic populations. However, major changes of small pelagic (abundance regimes) tend to occur on the interdecade scale, rather than with the interannual variability normally associated to ENSO. Despite some recent research, the role of ENSO variability at determining interdecadal climate variations (climate regimes) is still a matter of controversy. In this work, we searched for statistical relationships between small pelagic and climate regimes and ENSO activity, and between these and indices of extratropical and solar variations over the interdecadal time scale.

Climate regimes were detected within the Global Surface Air Temperature record and within other large-coverage air temperature series. Climate regimes seem to be global phenomena although the signal is not equally strong worldwide. A relationship is suggested between climate regimes and El Niño frequency and strength; warm (cool) regimes grossly correspond to periods of few and weak (many and strong) events. Warming (cooling) trends may be characterized as periods of low (high) Southern Oscillation Index (SOI) average values. It is also suggested the change from one regime to another tends to occur when extreme SOI values are reached.

Small pelagic regimes were defined from catch records of the main world fisheries: Japan, California, Humboldt, Benguela and Canary. A composite series (RIS) was constructed. This series is a good indicator of decadal-scale global changes since it tends to emphasize common long-term variability of the stocks while reducing the effects of the individual, year-to-year variations. Comparison between RIS and climate regimes strongly suggests global decadal variability is first evident at the boundary systems of the oceans where small pelagic stocks develop.

For the relationship between the ENSO - as a tropical mechanism - and the Aleutian Low - as a component of the extratropical climate system -, our results suggest that periods of relatively high solar activity tend to promote tropical-extratropical coupling; whereas indenpendent tropical-extratropical variability tends to occur at moderate to low solar activity. Worldwide sardine growing periods (upward RIS trends) seem to occur at moderate to low solar activity. Worldwide sardine growing periods (upward RIS trends) seem to occur when the tropical and the extratropical systems tend to behave independently. Anchovy growing is probably favored by coupled tropical-extratropical interdecal variability.

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