h broadbill swordfish, 1 yellowfin tuna, and a large number of 

 sharks, and returned to port on January 21, the first vessel 

 from this prefecture to engage in fishing in this areao Since 

 that time with the increase in the number of large vessels, 

 the fishing grounds have expanded and moved farther offshore 

 year by year, the center of the winter albacore fishery in 

 particular having moved to far distant waters o Ihe following 

 table will show this expansion and removal of the fishing 

 grounds from 1931 on o This eastward movement of the winter 

 fishing grounds almost ceased after 1936, and the fishing grounds 

 remained the so-called 1000-mile and 2000-mile grounds in the 

 vicinity of 26° to 33 No, along the line of the current boundary 

 (subtropical line of convergence) formed by the meeting of the 

 Kuroshio countercurrent, which splits off to the southward from 

 the main Kuroshio and the current running to the nortnwest along 

 the northern fringe of the North Equatorial Current, Ihe area 

 which forms the center of the fishing ground is at 170° to l80°Eo 

 longitude, west of Midway Island, an area where the meeting of 

 these currents is most pronounced (with high salinities of 35.^ 

 and upwards). Tuna fishermen already knew from experience that 

 good fishing grounds of restricted extent could be found in 

 this sea area where changes in water tenperatures and salinities 

 were sharpest. Although it has been stated that the fishing 

 grounds are now stationary, the center of the grounds moves a 

 little bit south from January to February and from February to 

 March, and the fishing grounds are at their farthest south 

 position in March when the 18° isotherm also reaches its south- 

 ernmost position. Favorable water tenperatures are the same as 

 in the coastal fishing grounds, 17° to 19° with 18° as the 

 center. The fishing season is roughly from November to March, 

 with the peak from around the middle of January to the middle' 

 of March. 



Note: 



(1) In 1938, the favorable water tenperatures in the 

 winter were from 17° to 19°„ 



(2) For the catch taken during the winter season see 

 the section on fluctuations in fishing conditionso 



As can be seen from the table, the greatest number of fish 

 are taken in the winter season at surface water temperatures 

 ranging from 17° to 19°, centering around 18 degrees. With 

 respect to salinity, aside from a peak at around 'jho6 to 3li,9 

 0/00, the greatest number of fish is taken at 35„5 0/00 or 

 higher. The fish are medium-sized (2^ to iiO pounds), small 

 (under 25 pounds), and some large ones (over UO pounds) are 

 also taken. 



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