As we have no data for the season of southerly winds, we know nothing of 

 oceanographic conditions at that tinne of the year. During the season when northerly winds pre- 

 vail, the water temperatures are in general higher than those of the Nicobar Islands region, with 

 slightly over 28 C. at the surface, slightly less than 28 C. at the 50-meter level, and around 

 24 to 25 C. at the 100-meter level on the average. Higher values are shown for transparency 



than in the Nicobar and Andaman islands waters, the values running about 30 meters, 

 water color is in most cases I or II on the Forel scale. 



The 



The season of southerly winds corresponds with the rainy season in this region and 

 there are many squalls. Wind and waves are generally high suid typhoons occur from time to 

 time. It is thought that the weather will interfere frequently with fishing operations. This sea 

 area, except for its northern extremity, is generally calm during the season of northerly winds 

 and fishing operations are usually very easily carried on. 



The investigations of the Haruna Maru and the Hakuyo Maru cover the period from 

 November through February. The data from the Shonan Maru were collected in August in the 

 vicinity of the Sunda Strait. It is said that the mothership-type operation of the Tobu Fisheries 

 Company also entered this area, but as there are no data from this venture we do not know what 

 conditions they found there. If we summarize these various data in a table, the fishing con- 

 ditions in this sea area may be shown as follows. 



Table 12. --Fishing conditions off the west coast 

 of Sumatra 



As the table shows, the combined catch rate for tunas and spearfishes is over 10, 

 indicating that this sea area is an extrennely good fishing ground. 



Compared with the waters of the Andannan and Nicobar islands described above, the 

 catch rates in this sea area are conspicuously higher. Yellowfin, bigeye tuna, and spearfishes 

 are all shown to be more abundant in this area. The shark catch rate on the other hand is 

 lower. The table shows that the nnain factor in the greater catch rate in this area is the in- 

 creased catch of yellowfin tuna, but note must also be taken of the remarkable increase in the 

 bigeye catch. 



The data are limited to the period from November through February, but they 

 afford a basis for considering that the seasonal changes in fishing conditions are fairly great. 

 The following table shows the catch rates for each species grouped by months. 



Table 13 brings together data from investigations covering several years. It may 

 naturally be thought that there is a certain amount of variation from year to year, however, for 

 the period from November through February, a general tendency for the catch rates to gradu- 

 ally rise with the passage of time can be clearly detected. Data for the season of southerly winds 

 are, as the table shows, very few and are inadequate as a basis for forming any sort of an 

 opinion, but it is thought that some catch can be anticipated at this season. 



46 



