34 



seldom found in Table Bay or to the north of Table Bay. 

 Unlike the Snoek, it is a shore-frequenting form, and it is of 

 significance that at Knysna, when cases of mortality among 

 fish occur, it is the species most seriously affected. 



These two cases illustrate the influence of the cold stream 

 in its extent along the coast. Other cases illustrate the up- 

 swelling of the cold water on the shores from under the warm 

 water, as it is the shore forms which are mostly affected. 



There seems little doubt, therefore, not only that the present 

 distribution of fish and marine fauna generally on the South 

 African Coast is determined by the cold Antarctic water meet- 

 ing the warm Agulhas current, but that the relative abundance 

 at different times may be due to the relative strength of the 

 opposing currents, the effect of the cold current being in 

 severe cases an extensive mortality in marine life, the 

 extension of the cold water for instance to the east, permitting 

 the presence of Snoek as far east as Port Elizabeth, and the 

 extension of the warm water permitting the presence of the 

 Red Stumpnose towards the west even occasionally to Table 

 Bay. If a pelagic rather than a rock-frequenting fish be 

 desired as an example comparable with the Snoek, Elops 

 saurus (the " springer " of Natal and " Cape Salmon " of Port 

 Elizabeth) may be cited, as it is common on the east coast 

 and only occasionally found as far west as Knysna. The 

 " Seventy-four " {Dentex undulatus) is another example of a 

 warm water fish. 



The cause of the warm Mozambique current on the east 

 coast, and its continuation as the Agulhas current on the south 

 coast, is the trade winds of the Indian ocean, which drive the 

 water from a south-easterly direction towards the Equator, 

 where it becomes heated up, and, as the Equatorial current, 

 impinges on the African continent, and is diverted along its 

 eastern shore. It is, therefore, on the east coast of South 

 Africa, turned southwards and encounters the south-east 

 trade winds in the modified form of the Cape south-easters. 

 These have a tendency to drive it back, or, at least, keep it in 

 check, so that the Antarctic current will extend further to the 

 east. It seems to be due to this that we have the apparently 

 anomalous fact that an on-shore wind (S.E.) is followed by 

 the appearance of cold water. 



There are, however, many obscure points regarding the 

 currents of the South African coast, which can only be cleared 

 up by a series of systematic observations. A good deal might 

 be done by observation of surface temperatures at stations 

 on the coast line, but it is essential that observations of tem- 





