Seasonal distribution and density of common dolphins Delphinus delphis off the south-east coast of southern Africa

Abstract

The seasonal abundance and distribution of common dolphins on the south-east coast of southern Africa, between Port Elizabeth and Richards Bay, was studied from aerial sightings made between March 1988 and August 1989. Common dolphins appear to be present between Port Elizabeth and East London throughout the year, but their density there is low. Farther north, along the coasts of Transkei and Natal, common dolphins are found only during winter, when they apparently migrate there at the same time as pilchard in the annual Natal "sardine run". Densities off Transkei and Natal are greater than they are off the Eastern Cape, but this may only be an artifact of the narrowness of the continental shelf in the north. Common dolphins have probably adapted to the plentiful food resources provided by the sardine run, and females may use the migration to wean their young and replenish energy reserves before their next pregnancy.