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Trends in the abundance and distribution of anchovy and sardine on the South African continental shelf in the 1990s, deduced from acoustic surveys
Abstract
The South African pelagic resources have been monitored acoustically since 1983. The results of these surveys are currently used to determine catch limits for anchovy Engraulis capensis and sardine Sardinops sagax. Two
main surveys are conducted annually, in winter to determine the strength of the year’s recruitment and in summer to estimate the size of the adult stock. The results of the surveys conducted between 1990 and 1997 are presented and discussed in the context of the time-series of stock abundance. Distribution patterns, size structure and biomass levels are related to general trends in the life-history strategies of anchovy and sardine, as well as the major environmental features in the southern Benguela in the 1990s. The biomass of adult anchovy appears to be driven largely by the strength of the early recruitment, corresponding to fish spawned in the first half of the summer spawning season. The biomass of adult sardine, however, is better explained on the basis of the biomass of 2-year-old and older fish in the previous year’s survey. Anchovy tend to move east with age, whereas
sardine appear to move both north, along the south African west coast, and east with increasing age.
main surveys are conducted annually, in winter to determine the strength of the year’s recruitment and in summer to estimate the size of the adult stock. The results of the surveys conducted between 1990 and 1997 are presented and discussed in the context of the time-series of stock abundance. Distribution patterns, size structure and biomass levels are related to general trends in the life-history strategies of anchovy and sardine, as well as the major environmental features in the southern Benguela in the 1990s. The biomass of adult anchovy appears to be driven largely by the strength of the early recruitment, corresponding to fish spawned in the first half of the summer spawning season. The biomass of adult sardine, however, is better explained on the basis of the biomass of 2-year-old and older fish in the previous year’s survey. Anchovy tend to move east with age, whereas
sardine appear to move both north, along the south African west coast, and east with increasing age.
