FISHERY BULLETIN: VOL. 72, NO. 4 



30 60 100 140 



40S 



400 



Figure 3. — Vertical distribution of oxygen along four north-south transects in the Indian Ocean: A - lat. 14°N to 36°S at long. 55°E 

 (February-March); B - lat. 24°N to 4rS at long. 60°E (August-November); C - lat. 18°N to 37°S at long. 70°E (May-July); D - lat. 13°N to 

 30°S at long. 92°E (August-September). (Charts reproduced from Wyrtki, 1971.) 



flows along the zone where the thermochne slopes 

 upward toward the Equator between lat. 10°S and 

 20°S. The general distribution of subsurface 

 isotherms is more or less similar across the full 

 breadth of the equatorial region. 



Wyrtki's figure { 1971:38) indicates the presence 

 of cold surface water in the northern part of the 

 Bay of Bengal during the NE monsoon. Banse 

 (1960) pointed out that the cold surface water in 

 this region may not be attributed to upwelling, but 

 to a high rate of evaporation caused by the dry air 

 from the continent. The coasts of northwest Aus- 

 tralia and Java are other regions reported to have 

 seasonal upwelling. Wyrtki (1961) pointed out 

 that there was intense upwelling in these two 

 areas during the SW monsoon. 



It is postulated that in the Indian Ocean wind- 

 driven equatorial upwelling is less intense than in 

 the Atlantic and Pacific oceans and may be totally 

 absent (Taft, 1971). The absence of substantial 

 peaks in the zooplankton biomass along the 

 equatorial regions of the Indian Ocean is consis- 

 tent with the idea of there being little equatorial 

 upwelling, compared at least with the Pacific 

 (King and Demond, 1953; Reid, 1962; Heinrich, 

 1968) and the Atlantic (Hentschel, 1933). 



In the Indian Ocean seasonal changes in surface 

 salinity are more pronounced in the Arabian Sea 

 and the Bay of Bengal than in any other region 

 (see Wyrtki, 1971). Throughout the year the sur- 

 face salinity was greater in the Arabian Sea than 

 in the Bay of Bengal. During the NE monsoon 

 surface salinity becomes very low (30-33%o in the 

 Bay of Bengal; advection of low-salinity water oc- 

 curs from the Bay of Bengal toward the western 

 Indian Ocean. As the Monsoon Current develops 

 during the SW monsoon, a tongue of high-salinity 

 water flows eastward. 



RESULTS 



Geographical Distribution of 



Neniatoscelis gracilis 



Indian Ocean 



Two forms considered to be ecophenotypes of A^. 

 gracilis are recognized to occur in the Indian 

 Ocean: an "old form" which is identical in mor- 

 phological character to the typical form described 

 by Hansen (1910) from waters of the Indo- 

 Australian Archipelago, and a "new form" which 



1046 



