THE ROLE OF ESTUARIES IN SOUTH AFRICAN FISHERIES: ECONOMIC IMPORTANCE AND MANAGEMENT IMPLICATIONS

Abstract

Existing catch data for 129 of 255 functional estuaries on the South African coastline were reviewed and the relationships between fish catch and estuary size, type and biogeographical region analysed using simple and multivariate models. The best predictive models were obtained by analysing data separately for each biogeographical region. Estuary size alone explained >80% of the variation in catch in the warm temperate region and >90% of the variation in catch in the cool temperate and subtropical region. Further analysis of the two main estuary types, i.e. permanently open and temporarily open/closed estuaries revealed a steeper regression slope and therefore greater productivity for the permanently open systems. Estuary size (ha) and type (five) were used to explain catches within the warm temperate and subtropical regions using general linear models. The models were able to explain 82 and 98% of the variance in catches for the two regions respectively, and both were significant (p < 0.001). These models were applied to estuary type and size data for all 246 estuaries in the two regions and a total catch of 1 840 tons per year was estimated. Including the cool temperate region the total estuarine catch in South Africa was estimated at 2 480 tons per year. In all, 50% of the estuarine catch was attributed to commercial seine and gillnet fisheries, 46% to recreational angling and 4% to traditional trap and spear fisheries. Total catch value was R433 million per year, of which 99% could be attributed to recreational angling. Estuarine contribution to the inshore marine fisheries was estimated at approximately R490 million per year, estuarydependent species constituting 83%of the catch of the recreational shore and commercial seine and gillnet fisheries and only 7% of the catch of the recreational spearfishery and commercial and recreational boat fisheries. In 2002, the total value of estuarine and estuary-dependent fisheries was estimated to be R1.251 billion.

Afr. J. mar. Sci. 25: 131–157