566 ECOLOGY AND BEHAVIOR 



slow-swimming shark of this size makes extensive migrations along the length 

 of the southern African coastline when a relatively short movement away 

 from the coast results in a marked change in environment. 



Holohalaelurus regani 



Holohalaelurus regani is a small catshark found on the outer parts of the con- 

 tinental shelf and on the continental slope along the south and east coast of 

 Africa from the southwestern Cape to East Africa. As shown in Figure 12, 

 specimens from the southwestern Cape can be distinguished from those 

 found off Natal. Those found off Natal are smaller than those from the 

 Cape, with males maturing at 45 to 50 cm and attaining a length of at least 

 55 cm and females maturing at 38 to 39 cm and growing to about 45 cm. In 

 contrast to most sharks, the males are larger than the females, a feature also 

 of the other member of the genus, H. punctatus. 



Another striking feature of this bottom-living, oviparous species is that the 

 young apparently live on the continental slope in deeper water than that nor- 

 mally occupied by the adults. Young H. regani also are markedly different 

 from their elders in appearance (Figure 13), being dark black in color both 

 dorsally and ventrally. "The overall dark colouration is reminiscent of that 

 found in deep-water squaloid sharks such as the genus Etmopterus and may- 

 indicate similar habits." (Bass et al. 1975a). 



The Genus Carcharhinus 



The genus Carcharhinus includes 28 species (Garrick 1967), of which 17 

 have been recorded from the southwestern Indian Ocean (Bass et al. 1973). 

 All are fairly fast-swimming pelagic species, ranging in length from about 1 

 to 4 m and armed with flattened cutting teeth. Of the 17 species from the 

 region, C. galapagensis has been found only at the Walters Shoal while C. 

 amblyrhynchos has been recorded only once (from the northwest coast of 

 Madagascar). The remaining 15 species are listed in Table 5 in descending 

 order of size as estimated from the lengths at maturity given by Bass et al. 

 (1973, Table 5C). 



Of these 15 species only C. longimanus is not a continental shelf inhabitant, 

 although even relatively small inshore species such as C. sealei and C. mel- 

 anopterus have been caught over deep water on occasion. C. longimanus has 

 a tropical offshore distribution and is commonly found over deep water off 

 Durban; it also ranges far southward in warm Agulhas Current water. For 

 instance, two specimens were taken some 400 km south of Cape Agulhas 

 where the surface water temperature was 21. 3° C. 



Thus, 14 species are normally found on the continental shelf. Most have 

 tropical distributions, only C. brachyurus having a warm temperate range 

 centered in the southern and southwestern Cape. This shark is caught in the 

 eastern Cape throughout the year and ranges north to southern Natal (oc- 

 casionally to central Natal) in the winter months. C. altimus is markedly dif- 

 ferent from all the other species in that it is usually caught on or near the 



