Tropical South-East Atlantic response to ENSO as an ecosystem indicator for the southern Benguela

Abstract

The response of the tropical South-East Atlantic Ocean to the El Niño Southern Oscillation (ENSO) was studied for the period 1950–1999. Interaction between the ocean thermocline ‘see-saw' and the overlying zonal wind circulation was examined. The two are closely linked through equatorial upwelling dynamics, with the thermocline leading during most of the period. Composite differences in climatic structure in respect of ENSO phase were analysed. Cases were selected based on indices of Pacific sea surface temperature and South-East African rainfall. Prior to an El Niñoinduced drought, anomalous easterly flow over the Atlantic strengthens the cold tongue extending from Angola. How these climatic conditions affect fisheries abundance in the southern Benguela was investigated. Higher anchovy Engraulis encrasicolus catches tend to follow an El Niño event, and higher sardine Sardinops sagax catches tend to follow a La Niña event, through the northward and southward shift respectively of the South Atlantic anticyclone and attendant coastal upwelling. In the southern Benguela, enhanced westerlies and warmer water favour anchovy catches over sardine catches. Recognition of the climatic patterns that impact fisheries abundance represents a potential management tool.

Keywords: Benguela fish catch, climate variability, El Niño impacts

African Journal of Marine Science 2006, 28(1): 41–50