This was most likely a juvenille smooth Hammerhead Sphyrna zygaena, It is not so unusual in the Western Cape they are found worldwide in warm temperate and tropical seas, both inshore and offshore.
They are however listed as vulnerable on IUCN due to the fact that they are caught in many fisheries and their fins are valuable. As adolescents they often spend their time on the surface of the water with their dorsal breaking the surface, especially in warm sheltered/estuarine environments. It would be uncommon for this species to appear at a cage diving boat here as white sharks would be a natural predator to it as a juvenile (in Kleinbaai anyway). The species can reach lengths of up to 4.2m TL.
Interestingly walking on Pearly Beach the other day we found loads of tiny squid bones most likely from chokka (Loligo vulgaris) a known prey species for this type of Hammerhead shark. As they grow larger these Hammerheads can then consume stingrays and smaller sharks.
Cool sighting, I haven't personally seen them in Kleinbaai since January 2007 although I've heard many reports from local fishermen and others in Mossel Bay and False Bay. Usually when they are seen here its when water temperatures are warmer at the surface, in summer.
