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Figure 2. — Distribution of M. indica around the southern tip of Africa by quarter of the 

 year. Catch rates (per 100 hooks) represented by number of dots in each 5° square 

 (one— <0.001, two— 0.001-0.004, three— 0.005-0.009, four— 0.01-0.04, five— 0.04-0.1, 

 six— >0.1). 



are noteworthy. Judging from the catch rates there is 

 always a fair black marlin population present in the 

 southwest Indian Ocean. At all times of the year, 

 except midwinter, a certain number of the fish move 

 into the sea area west and south of the Cape of Good 

 Hope, but are apparently most numerous there in the 

 summer period, January to March. 



At various times records of the black marlin are 

 found well into the Atlantic within the area covered 

 by the present report. Wise and Davis (1973) have 

 recorded catches of this species over a wide area of 

 the Atlantic, but in all cases the records are based on 

 Japanese catch statistics. Apparently none of the 

 fish have been examined by an ichthyologist. On the 

 other hand the skippers of the Japanese boats can be 

 assumed to be familiar with the different marlins and 

 their distribution and will presumably check any 

 identification as unexpected as this. It has become 

 almost a theorem that the black marlin does not 

 occur in the Atlantic, and there is the resultant 

 danger that any large marlins found in the Atlantic 

 will be identified as blues without adequate examina- 

 tion. 



Catch rates west of long. 20°E are never as high as 

 those east of this meridian, but there is a suggestion 

 of a northwesterly movement of the stocks from the 

 southern tip of Africa as summer advances and a 

 withdrawal with the onset of winter. It is suggested 

 that the black marlins present in the Atlantic are fish 

 that have entered the Atlantic in eddies of warm 

 Agulhas water at this time and are then trapped by 

 cold water, preventing their return to the Indian 

 Ocean. 



Similar catch statistics have been plotted for the 

 blue marlin. These are shown in Figure 3. On the 

 basis of the very few catches made off the Cape by 

 local vessels, it was thought that the blues were of 

 Atlantic origin. The more widespread catches of the 

 Japanese fishing industry, however, suggests that at 

 least some of the blues may actually be of Indo- 

 Pacific origin. Between January and June there is a 

 widespread but low catch round the southern tip of 

 Africa, but as winter progresses there is apparently a 

 movement offish away from the Cape, and diffusely 

 distributed fish then resolve into two populations, an 

 Atlantic one and an Indo-Pacific one, although a 



179 



