TOP PREDATORS IN SOUTHERN AFRICA'S MARINE ECOSYSTEMS

SUMMARY

South Africa's marine ecosystems have a wide variety of top predators, including both cartilaginous and teleost fish, 15 breeding seabirds and many more that are migratory to the region, seals, whales and smaller cetaceans. Land-breeding seabirds and seals were readily accessible to early colonists, and together with the obvious larger whales, were among the earliest marine resources to be exploited intensively. A number of species had been reduced to low levels by the start of the 20th century. Early research had two main objectives, in the case of exploited species investigation of factors influencing yields, and in the case of non-utilized species, such as many of the region's fish, the documentation of species. The landing of whale carcases at mainland whaling stations provided opportunity to investigate the biology of larger whales. As fisheries on the prey of top predators developed, some of the predators were regarded as competitors of fishermen. Research then aimed to quantify the competition, and included investigation of population size, diet and consumption, and species interactions in an ecosystem context. As fisheries expanded, some prey stocks collapsed and some seabirds decreased in abundance. This prompted research into the use of seabirds as indicators of the state of fish resources. In KwaZulu-Natal, attacks by sharks on man led to research aimed at reducing the incidence of attacks and the introduction of shark nets, which, due to their non-selectivity, had an influence on several species. Direct exploitation, depletion of prey resources, and incidental mortality, such as in the shark-net fishery, led to deterioration in the conservation status of several of South Africa's top predators, notably some sparids, seabirds and cetaceans. Consequently, much recent research has addressed issues of conservation concern, with the aim of securing sound management of predator populations. Issues of continuing concern include scarcity of food, incidental mortality and oiling and other forms of pollution. Top predators are expected to earn considerable revenue through ecotourism and recreational pursuits, and this is likely to become a focus of future research. Because of the migratory nature of many top predators, it is foreseen that their management will become multinational and it is expected that the funding basis for research will broaden to include non-governmental agencies. The advancement of technology will lead to automation of some monitoring studies and increased understanding of at-sea behaviour. The discovery during the celebrations of 100 years of marine science in South Africa of a fifteenth species of seabird breeding in the country suggests that the era of exploration and documentation has not yet closed.