The only records concerning sizes of fish taken are the data fronn the Shonan Maru's 

 operations. Of 402 yellowfin taken in the course of the Shonan Maru's work, the snnallest 

 was 2.8 kilograms, the largest 58 kilograms, and the average weight was 33 kilograms. Figure 

 10 shows the weight frequencies of these fish by 3-kilogram classes. 



As figure 10 shows, fish of 

 about 35 - 38 kilograms were most 

 nunnerous, with another peak at 4 I - 44 

 kilograms. In the smaller sizes, there 

 was a rather conspicuous peak at 8 - 11 

 kilograms. If we apply to these 

 Professor Aikawa's age determination 

 method, the peak of small fish repre- 

 sents fish in their fourth year, while 

 the great majority are seventh- and 

 eighth-year fish. The size distribution 

 by latitude is not clear, but there seems 

 to be some tendency for fish to be larg- 

 er in the north and smaller in the south. 

 The average weight of 33 kilograms is 

 about the same as that for the former 

 South Seas Mandate and is thought to 

 show the identity of the populations. 

 Nothing at Eill is known of seasonal 

 chajiges in the size of the fish. 



Figure 10, 



WEIGHT (kg) 



--Yellowfin weight frequen- 

 cies (E, Philippines Sea) 



Weights of black marlin have 

 been divided into 10-kilogram classes and their frequencies plotted as shown in figure U, The 

 data, like those for the yellowfin, are from the investigations of the Shonan Maru and the number 

 of fish is 165. As is clear from the figure, there is a very pronounced peak at 40 - 50 kilograms. 



The curve falls off steeply in the smaller 

 sizes and also in the larger sizes. It is 

 an interesting fact that a great majority 

 of these fish were males, females being 

 only 9 percent of the total and almost all 

 of these were a very large size. Judg- 

 ing from a number of data, it appears 

 that fishing from the central section on 

 northward is subject to violent seasonail 

 fluctuations, and after September the 

 composition of the catch changes and 

 fishing suddenly becomes poor. Sea- 

 sonal fluctuations do not seem so vio- 

 lent in the southern part of the area, but 

 on the whole it is the season of south- 

 westerlies which shows the best fishing. 

 This pattern is thought worthy of note as 

 it appears also in the former South Seas 

 Mandate and is particularly marked in 

 the Celebes Sea, 



The foregoing facts indicate 

 that, if area and season are taken into 

 account, this region will jilso offer very 

 superior fishing grounds. 



Figure 11. 



WEIGHT (kg) 



--Black marlin weight fre- 

 quencies (E. Philippines 

 Sea) 



77 



