As the figure clearly shows, black tuna have a catch rate of slightly under 1.0 in the section from 

 130 to 132 E. longitude, but farther to the east the decline in the catch rate is extremely con- 

 spicuous. The yellowfin catch rate is very low with little difference throughout the whole area. 

 The bigeye tuna decrease somewhat in the section between 132 and 134 E. longitude, and tend 

 to increase steadily to the eastward. Spearfishes decrease gradually from the extreme west 

 toward the central portion, then increase sharply in the vicinity of the Izu Islands until the catch 

 rate is slightly over 1.0. Albacore show a conspicuous increase in the central part of the area, 

 where the catch rate is 4. 2. 



In the extreme western section around Tanegashinna black tuna are the most important 

 element in the catch, in the central part around the Kinan Shoals albacore are the main species, 

 and in the far eastern section around the Izu Islands spearfishes make up the greater part of the 

 catch. This situation is very clearly shown by the figure. 



In order to see the seasonal changes in the fishing, catches for each month have been 

 shown in table 69. The inequality in the seasonal distribution of the data is very great, and for 

 this reason it is difficult to grasp fully the changes from month to month in fishing conditions. 

 Leaving aside all considerations of areas and sunnmarizing the data for this sea area as a whole, 

 it is shown that black tuna are more abundant in the winter, with their highest catch rates for the 

 ye £ir from March through April. Yellowfin are generally scarce, but they increase somewhat 

 around April and then have their highest catch rates for the year from October through November. 

 Bigeye tuna are not taken at all during the summer, their highest catch rate for the year being in 

 October, after which they gradually decline. Albacore are hardly taken at all during the summer; 

 their catch rates gradually improve from December to February, after which they decrease 

 suddenly in March. 



The foregoing is based exclusively on the longline fishery with no consideration of the 

 pole-and-line fishery. The pole-and-line catch is fairly large at certeiin seasons, but the fish 

 taken are generally small. 



In addition the fishery with fixed gear takes Sonne yellowfin and black tuna, and the 

 catch in certain years is fairly considerable. The fishing season for these fisheries is mainly 

 in the summer. 



The situation is not entirely cle2ir because there are very few data for July and none 

 at all for August and September, but it is shown that in general spearfishes are abundant in the 

 summer, with a truly high catch rate of 6.8 in June, showing that considerable catches can be 

 anticipated. This high catch rate is based on data obtained almost entirely from the waters adja- 

 cent to the Izu Islands. There are no data for other parts of the area so they cannot be shown, but 

 it appears that in recent years a large number of harpoon boats have operated in the Hyuga Nada 

 area with fairly good success, the season extending from 2 to 3 months centered around May. 



Fishing for spearfishes in the Ogasawara Islands area, which adjoins the Izu Islands 

 area on the south, is, as has already been stated, good from April through July in the northern 

 section (25 to 30 N. ), with the catch rate reaching a high in May of 4.2. Consequently it is 

 thought that there is a lag of about 1 month between the pealc of the spearfish season in the north- 

 ern Ogasawaras jmd the waters adjacent to the Izu Islands. 



As was stated earlier, in the winter the central part of this region produces a large 

 adbacore catch, and in the most westerly part the black tuna fishery is at its peauk. In the summer 

 there is a general tendency for the spearfish catch to increase markedly, this trend being partic- 

 ularly conspicuous in the waters adjacent to the Izu Islands. However, the fishing season is 

 short. From October on there is some increase in the yellowfin and bigeye catch. 



The overall catch rate throughout the year is shown to be slightly more than 2. 7, but 

 if the distance between the bases and the fishing grounds is taken into consideration, it is not 

 correct to say that the grounds of this sea area are very inferior. Besides the tuna and 



101 



