ECOLOGY: INDIAN OCEAN SHARKS 571 



used as a primary nursery gound by C. breuipinna but only rarely by C. 

 limbatus, which probably drops its young off Tongaland or southern 

 Mozambique. To complicate the issue, somewhat older (but still immature) 

 C. limbatus are not uncommon in Natal where C. breuipinna of a similar age 

 are rare. It seems possible that C. breuipinna of this age group live to the 

 south of Natal. 



The four remaining sharks (C. sealei, C. melanopterus, C. sorrah, and C. 

 spallanzani) are relatively small species with narrow, oblique cusps to the 

 teeth of both jaws. C. sealei is by far the smallest Carcharhinus species of the 

 region, maturing at about 75 cm and rarely attaining more than a meter in 

 length. It appears to tolerate a wider range of environmental conditions than 

 the other three small species, none of which ranges south of Tongaland. C. 

 sealei has been recorded throughout the tropical parts of the southwest 

 Indian Ocean and is not uncommon in the seas of northern and central Natal. 

 In coral reef areas it seems to be less abundant than the other three sharks. 

 In such conditions C. melanopterus is abundant in the very shallow waters 

 of the lagoons and the channels joining the lagoons to the open sea. The 

 slightly larger C. sorrah prefers the shallowest waters outside the lagoons, 

 while the even larger C. spallanzani inhabits somewhat deeper waters, only 

 the juveniles regularly coming into very shallow areas. The latter species is 

 common on the Tongaland coast while the other two are more strictly tropi- 

 cal and do not occur to the south of Delagoa Bay. 



The Carcharhiniform Sharks 



The genus Carcharhinus cannot be considered completely on its own, for 

 many other sharks live on the east coast of southern Africa, some of them 

 competing in one way or another with the various species of Carcharhinus. 

 For a start we can consider the group commonly known as the carcharhini- 

 form sharks. This includes the sharks of the families Scyliorhinidae, Pseudo- 

 triakidae, Carcharhinidae, and Sphyrnidae. These four families are not 

 clearly demarcated from one another but instead form arbitrary divisions in 

 a morphological gradient ranging from sluggish, bottom-living types 

 (scyliorhinids) through faster but demersal types (Pseudotriakis and the 

 "lower" carcharhinids) to fast pelagic forms inhabiting open water ("higher" 

 carcharhinids and the sphyrnids). 



Sphyrnids and "Higher" Carcharhinids— Apart from the genus Car- 

 charhinus, nine "higher" carcharhinids and three sphyrnids are found on the 

 east coast of southern Africa (see Bass et al. 19756). The general pattern of 

 distribution is much the same as in Carcharhinus, with a predominance of 

 tropical species living in inshore waters. Among the carcharhinids there is 

 one offshore species (Prionace glauca) with a temperate distribution as com- 

 pared to the tropical Carcharhinus longimanus. A further inshore species 

 (Galeorhinus galeus) has a temperate distribution ranging from the south- 

 western to the eastern Cape. This is a medium-sized shark maturing at 120 



