Figure 9. — Surface temperatures and salinities off South Africa, October 1961. A. Temperature. B. Salinity. 



Atlantic Surface water is being reduced by the reas- 

 sertion of the Agulhas Current's westerly extension 

 (>20°C and 35.4°/oo) and the formation of a distinct 

 Agulhas Bank mixed water zone. The Agulhas ex- 

 tension is mild and extends only to lat. 37°S, some 

 140 nautical miles from the coast. However, the 

 Bank water is well marked (<16°C and >35.4°/oo) on 

 the Bank itself, and also shows an interesting high 

 salinity intrusion (>35.4%o) round the Cape of Good 

 Hope up to lat. 34°S. The South East Atlantic Sur- 

 face water is present at long. 18°E although remain- 

 ing more than 40 nautical miles offshore. At 100 m, 

 the presence of the South East Atlantic Surface 

 water is more strongly felt and it extends eastward to 

 nearly long 20°E. A portion of the Agulhas Return 

 Current is present on the eastern edge of the Bank 

 as part of a powerful eddy, similar to "eddy A" 

 described by Bang (1970b). 



Despite the reestablishment of the Agulhas Cur- 

 rent in the survey area, the contribution of the 

 Indo-Pacific fauna is likely to be small. The tongue 

 of Agulhas Bank mixed water which extends around 

 the Cape of Good Hope may allow Indo-Pacific 

 billfish to move west, but the limited westward 

 penetration of the Agulhas Current itself makes this 

 occurrence less likely. The South East Atlantic Sur- 

 face water dominates the remainder of the survey 

 area, bringing with it the strong likelihood of Atlantic 

 billfish occurrence farther offshore than 40 nautical 

 miles. Thus in this period there is a strong possibility 



of both Atlantic and Indian Ocean forms being pres- 

 ent, but with more chance of Atlantic species. 



Summer, January 1962 



(Fig. 10a,b) 



Surface conditions at this time give an excellent 

 example of the interplay between the four water 

 masses off southern Africa. The Agulhas Current is 

 present as a coastal tongue east of long. 21°E, con- 

 tributing to the Agulhas Bank mixed water, and as a 

 strong westward extension south of lat. 36°S. The 

 Agulhas Bank water is clearly defined «20°C and 

 <35.5°/oo) and extends from the coastward portion of 

 the Bank westwards around the Cape of Good 

 Hope, where it creates a dramatically steep gradient 

 with the upwelled water. Between the Agulhas Bank 

 water and the Agulhas Current Extension is a large 

 intrusion of South East Atlantic water which ex- 

 tends across the southern portion of the Agulhas 

 Bank. At 20 m the continuity of the Agulhas Bank 

 mixed water around the Cape of Good Hope is very 

 clearly marked. 



Thus an interesting situation prevails: Indo- 

 Pacific billfishes could be present either close in- 

 shore between the Agulhas Bank and around the 

 Cape of Good Hope to lat. 33°S or south of lat. 36°S, 

 in the Agulhas Extension. Between these areas the 

 likelihood of Atlantic billfish occurrence is high, 

 with particular interest in the fact that the South East 



185 



