FISHERY BULLETIN: VOL. 72, NO. 4 



wo- ISO- 



20* 30- 40* 50* 



30* IW* IW 



Figure 4. — Locality records and daytime abundance of larvae and juveniles of Nematoscelis gracilis and N. megalops in the Indian 

 Ocean: a - NE Monsoon period. (Solid lines represent approximate distribution boundaries of N. gracilis and wavy lines represent those 

 of AT. megalops. ) 



from Figures 14.1 and 14.2 of Neumann and Pier- 

 son, 1966) and to which the South Equatorial Cur- 

 rent contributes, transports some of the new forms 

 to the south and the Agulhas Current transports 

 them to the tip of South Africa. 



During the SW monsoon the distribution of the 

 new form is much broader in the west than in the 

 east (Figure 5b). As the strong Somali Current 

 begins to flow northeastward, a great deal of 

 Southern Hemisphere water is brought to the 

 north along the African coast. Thus the population 

 of the new form is brought north of the Equator. It 

 was caught as far north as lat. 8°N along the coast 

 of Somalia; but it did not reach the upwelling 

 areas of the Arabian coast. It has been suggested 

 that the Somali Current turns eastward after 

 reaching lat. 8°N and joins the Southwest Mon- 



soon Current flowing east (Taft, 1971); the dis- 

 tribution of the new form in the upper layer fol- 

 lows the same pattern (Figure 5b). Except in the 

 area of the Somali Current, the overlapping zone 

 was conflned to the eastern ocean. The inter- 

 mediate forms were distributed across the 

 equatorial ocean. In the region of the Mozambique 

 Current new forms were found as far south as lat. 

 30°S. 



Populations of the old form in the Bay of Bengal 

 and the Arabian Sea show seasonal changes in the 

 abundance of larvae and juveniles (Figure 6). All 

 the available IIOE plankton samples from these 

 two areas were used to prepare these monthly 

 frequency distributions. In the Bay of Bengal the 

 highest frequency of calyptopis larvae was ob- 

 served in February, whereas in the Arabian Sea it 



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