576 ECOLOGY AND BEHAVIOR 



appears to be replaced by juvenile H. griseus. Adult H. griseus are usually 

 found in tropical waters. 



Squatinidae— Sq uatina africana, the only representative of this group 

 in the southwest Indian Ocean, grows to slightly more than a meter in length 

 and is found in shallow water and on the continental shelf from southern 

 Mozambique to the eastern Cape. It is adapted to living on the seabed, and 

 its ecological position is among the batoid fishes rather than the sharks. 



Pristiophoridae— The sole representative of this group in the region is 

 Pliotrema warreni, a small (up to 136 cm) sawshark found on the continental 

 shelf from the southern Cape to central Natal and occasionally in the south- 

 western Cape and in southern Mozambique. This shark also belongs among 

 the batoid fishes in any ecological classification. 



Oxynotidae— No members of this group have been found on the east 

 coast, the nearest records being two Oxynotus from the southwestern Cape. 



Dalatiidae— This family of squaloid sharks is represented off the east 

 coast of southern Africa by a continental shelf species and at least two dwarf 

 pelagic species living in deep water. The latter include Euprotomicrus 

 bispinatus, a well-known shark with an antitropical distribution, and 

 Heteroscymnoides marleyi, known only from a single juvenile washed up on 

 a Durban beach. The tropical pelagic delatiid Isistius brasiliensis may yet be 

 found in the Mozambique channel. The continental shelf species is Dalatias 

 licha, a sluggish shark of medium size ranging northward from the southern 

 Cape to at least southern Mozambique. 



Echinorhinidae— The medium-sized Echinorhinus brucus is fairly 

 common in the continental shelf areas of the Cape coasts but is rare in Natal, 

 where occasional specimens are caught in the southern areas. 



Squalidae— The taxonomy of the squalid sharks is still rather con- 

 fused, and it would serve no purpose here to consider their distribution in 

 any detail. Suffice it to say that they are basically small and medium-sized 

 demersal sharks competing to some extent with the "lower" carcharhinids, 

 from which they differ in the possession of cutting rather than grasping or 

 crushing teeth. Found on the continental shelves and in deeper water in 

 temperate and tropical areas, many of the species have wide distributions. 

 The squalids are among the most numerous of sharks, both in actual numbers 

 and in numbers of species. 



INTERACTIONS BETWEEN SPECIES 



In an article entitled "Social Organization of Shark Populations" Stewart 

 Springer (1967) gave an excellent analysis of the ways in which the distribu- 

 tion of sharks can be affected by inter- and intraspecific reactions. Apart 

 from emphasizing the need for consideration of size and sexual segregation 

 when describing the distribution of any species, he put forward the idea that 



