The Cape of Good Hope: A Hidden Barrier to Billfishes 



M. J. PENRITH' and D. L. CRAM- 



ABSTRACT 



Since 1838 there have been isolated reports of billfishes from the southern tip of Africa, but only during 

 the years 1961-64, when a number of Cape Town based boats fished commercially for tuna using longlines, 

 were billfishes found to occur in considerable numbers. 



The waters to the west and south of the Cape of Good Hope were found to be unique in their billfish 

 fauna, no less than six species being represented, comprising.YipAws, Makaira ( 2 species) and Tetrapturus (3 

 species). Only two wide-ranging species have not been found. Istiophorus is commonly listed from the area 

 on the basis of Histiophorus granulifer, but a reexamination of de Castelnau's type shows it to be a 

 Makaira, while T. angustirostris could occur as it is known from off Durban. 



The billfishes are probably attracted to this limited geographic area by the rich feeding grounds which 

 are the result of the upwelling of nutrient-rich water along the Cape's west coast. It is difficult, however, to 

 suggest reasons why there is an apparent barrier to movement between the Atlantic and Indo-Pacific 

 Oceans for certain species. Hydrographic conditions in the area are discussed, but there are no obvious 

 physical barriers preventing black and striped marlins from entering the Atlantic nor white marlin and 

 longbill spearfish from moving into the Indo-Pacific. 



The African landmass is unique, since of all the 

 major landmasses it alone does not project suffi- 

 ciently polewards to form a complete barrier to the 

 east-west movement of all the larger mobile warm- 

 water oceanic fish. All the same, it has traditionally 

 been considered a barrier to the movement of bill- 

 fishes between the Atlantic and Indo-Pacific 

 Oceans. This concept of a barrier has to a large 

 extent been strengthened by the very marked differ- 

 ences in the inshore marine fauna of the two sides of 

 the southern African coast (Ekman, 1953). 



The term Cape of Good Hope can be used for any 

 of three areas. In the strict cartographic sense it is a 

 minor land projection to the west of Cape Point on 

 the southern end of the Cape Peninsula. Historically 

 it embraced the area from about Cape Columbine to 

 the region of Cape Agulhas; this was the area where 

 the early East-Indiamen made their first landfall 

 when rounding the tip of Africa. Finally, the 19th 

 century biologists used the Cape of Good Hope in a 

 very wide sense to include the whole southern tip of 

 Africa and its adjacent seas. In this paper the Cape 

 of Good Hope is used in the same sense as the early 

 navigators used it, that is to include the land and 



'Stale Museum, Windhoek. South West Africa. 

 -Division of Sea Fisheries. Beach Road, Sea Point. Republic of 

 South Africa. 



adjacent seas to the south and west of the Cape 

 Peninsula (Fig. 1). Following the conventional divi- 

 sions of the oceans this area is within the Atlantic 

 Ocean, but is in reality a very confused area for the 

 oceanographer. Water from at least four sources can 

 occur as surface water in the area, being either sur- 

 face water of South Atlantic or Indian Ocean 

 (Agulhas Current) origin, mixed Agulhas Bank 

 water, orupwelled water of probably South Atlantic 

 Central water origin (Shannon, 1966; Visser, 1969). 

 The exact position of these water masses in relation 

 to each other is dependent on a number of factors, 

 but the direction and strength of the winds, both 

 local and as far removed as the monsoons of the 

 northern Indian Ocean, are the dominant factors. 

 The hydrography will be described more fully 

 below, but in general there is an east-west oscilla- 

 tion of Atlantic and Indian (Agulhas Current) sur- 

 face waters with southerly and westerly movements 

 of upwelled water. 



The first record of a billfish from the Cape of Good 

 Hope was the description by Gray (1838)of /"errap- 

 turus herschelii (= Makaira nigricans). Thereafter 

 there were very few records of billfishes indeed 

 (Table 1), with the exception of a number of catches 

 of Xiphias gladius since 1956 by deep-water trawl- 

 ers. 



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