The Distribution of cetaceans off the coast of South Africa and South West Africa / Namibia

[摘要] Thirty - seven species of cetacean are recorded from southern African waters. Four thousand, fivehundred and thirty - seven records of approximately 60 000 cetaceans were analysed to defmedistribution patterns of these species, including dedicated sightings (both scientific and commercial),incidental sightings, commercial catches and specimens. Records of dedicated scientific sightings andincidental sightings were analysed by water depth, sea surface temperature and salinity and season, whilecommercial sightings and catches were analysed by month and water depth.Of the thirty - seven species recorded within the region, four mysticetes and one odontocele could bedescribed as migratory, having a marked seasonal occurrence within the region, three species weredefmed as possible migrators as they were not recorded in the dedicated data and showed seasonality inthe incidental sighting and specimen databases, 20 species (19 odontocetes and one mysticete) could bedescribed as resident (in that they were found throughout the year) and five species were termed semi -resident (certain components or forms of which showed strong seasonal occurrence, while otherindividuals had a year- round occurrence). Records of a further four species were too few to defmedistribution patterns or seasonality.Analysis of the distribution of the large species showed three species (Eubalaena australis, Megapteranovaeangliae and Caperea marginata) to occur in nearshore waters and four species (Balaenopteramusculus, B. physalus, B. borealis and P.macrocepha/us) to occur in deep waters only. B.acutorostrata was recorded in both nearshore and offshore waters, while the two forms of B. edeni werefound in nearshore and offshore waters respectively.The distribution analyses of the smaller odontocele species showed a number of component patternsincluding cosmopolitan, pelagic cosmopolitan, tropical, sub tropical and warm temperate components of the Agulhas Current, warm temperate component of the south coast, a component of the Agulhas Bank,a south and east coast inshore component and west coast inshore and offshore components. The highdiversity of species within the region results from the complex variety of zoogeographic componentsfound within the relatively small study area. These arise from the complex oceanographic conditions,brought about by the upwelling of cold Central Atlantic water inshore on the west coast, the movementof subtropical water into the east coast region by the Agulhas Current and the mixing of Benguela andAgulhas Current waters to the south of the sub - continent.

[发布机构] University of Pretoria