572 ECOLOGY AND BEHAVIOR 



to 140 cm. The seven remaining species, all having tropical distributions, 

 divide by size as follows: 



Maturing at less Rhizoprionodon acutus 



than 150 cm Loxodon marcrorhinus 



Hypogaleus hyugaensis 

 Triaenodon obesus 



Maturing at more Hemipristis elongatus 



than 150 cm Negaprion acutidens 



Galeocerdo cuuieri 



Among the four smaller species, both Rhizoprionodon acutus and Loxodon 

 macrorhinus are active pelagic sharks with oblique, single cusps to the teeth 

 of both jaws. Both species are widespread along the east coast of Africa but 

 R. acutus, a common shark of the Natal coasts, is apparently more tolerant 

 of dirty water than is L. macrorhinus, which is confined to the clear water to 

 the north of St. Lucia. Hypogaleus hyugaensis is a poorly known species 

 similar in morphology to the rather sluggish Galeorhinus galeus. It is found 

 occasionally in Natal waters as far south as Durban. Triaenodon obesus is 

 another tropical shark apparently confined to clear water, for it is fairly 

 common on the Tongaland coast but has never been recorded south of St. 

 Lucia. A tough-skinned and slow-swimming but agile shark, it is normally 

 found near reefs where it feeds chiefly on crustaceans. 



Of the three large species, only Galeocerdo cuuieri occurs regularly south 

 of St. Lucia. A notorious scavenger with an appetite for anything from tin 

 cans to human beings, it breeds in tropical waters with a few immatures and 

 nonbreeding adults coming south into Natal and occasionally into eastern 

 Cape waters. Negaprion acutidens appears to be confined to the clear waters 

 of Tongaland and northward while little is known about the distribution of 

 Hemipristis elongatus. Apparently it is fairly common in the northern Indian 

 Ocean; specimens have been recorded from East Africa and from northern 

 Mozambique, and a lone straggler was caught in a shark net on the southern 

 Natal coast. 



The three sphyrnid sharks found in the southwest Indian Ocean are mem- 

 bers of the genus Sphyrna. The largest species, S. mokarran, is a widespread 

 tropical species found as far south as the Natal coast where it occurs regularly 

 but not commonly. All reproductive activities, including the nursery areas, 

 seem confined to tropical waters. A similar situation exists for S. lewini ex- 

 cept that a few newborn young have been taken off Natal and large numbers 

 of juvenile (but not newborn) sharks are found in the area during the summer. 

 S. zygaena, by contrast, has a distribution centered along the southern coast 

 of South Africa and is seldom caught off Natal where occasional specimens 

 are taken during the winter months. 



Pseudotriakis and "Lower" Carcharhinids— Psewdo triakis microdon is a 

 large (3 m) deepwater shark that probably occurs off the east coast of south- 

 ern Africa but has not yet been definitely recorded there (specimens have been 



