Aerial census of whale sharks (Rhincodon typus) on the northern KwaZulu-Natal coast, South Africa

摘要

A project was initiated to assess the potential for dedicated whale shark diving on the northern KwaZulu-Natal (KZN) coast of South Africa. Between October 2001 and September 2002, 12 aerial surveys were conducted along 350km of the coastline immediately south of the South Africa/Mozambique border. Only eight whale sharks were seen, with a sighting rate of 0.21 sharks per 100km of coastline. Another 13 surveys were completed during the summers of 2003/2004 and 2004/2005 and a total of 30 sharks were sighted, with a mean sighting rate of 0.69 sharks per 100km of coastline. The density of sharks was highest in the far north where it averaged 1.05 sharks per 100km between January and May but this value is considered too low to support dedicated whale shark diving. Local dive operators and light aircraft pilots confirmed the scarcity of whale sharks in the region. The mean sighting rate from three flights along 950km of southern Mozambique coastline in March was 5.6 sharks per 100km of coastline. Reasons for the marked regional differences in shark density are not apparent but the paucity of sharks in northern KZN waters may be linked to a recent increase in sightings off the Kenyan coast.