Pacific, 141 from the equatorial Pacific between 

 160° W. and 150° E. , 42 from east of Australia , 

 and 125 from the Indian Ocean. Meristic charac - 

 teristics showed no differences. Differences in 

 morphometric characteristics lead to the con- 

 clusion that there exist distinct populations in 

 the North Pacific, the southwest Pacific , and the 

 Indian Ocean, although there exists the possi- 

 bility of some mixing between the latter two 

 areas. 



One thousand fifty-seven yellowfin tuna 

 were examined, including 353 from the north- 

 west Pacific, 375 from the equatorial Pacific, 

 94 from the Coral Sea, 60 from the Banda Sea, 

 and 175 from the Indian Ocean. Similarities and 

 differences in morphometric characteristics 

 lead to the conclusion that there are a number of 

 independent or semi-independent populations 

 within each major area, somewhat restricted in 

 distribution, and probably intermingling with 

 adjacent groups. 



Six hundred ninety-seven bigeye tuna 

 were examined, including 313 from the north- 

 west Pacific, 284 from the equatorial Pacific 

 between 130° W. and 120° E. , and 100 from the 

 Indian Ocean. Although some differences were 

 observed, no definite conclusions were drawn 

 owing to conflicting biological information and 

 the need for more data. It is probable that big- 

 eye population structure is intermediate between 

 that of albacore and yellowfin. 



Inoue, Motoo 



Relation of sea condition and ecology of 

 albacore in the northwest Pacific 

 Ocean. /Conference Paper V - i.J 



( See also Inoue, Motoo. Studies on 

 movements of albacore fishing grounds 

 in the Northwest Pacific Ocean-I, II, 

 III. Bulletin of the Japanese Society 

 of Scientific Fisheries, vol. 23, no. 11, 

 p. 673-679 (19 5 8); vol. 25, no. 6, 

 p. 424-430 (1959); vol. 26, no. 12, 

 p. 1152-1161 (I960).) 



It has been hypothesized that a 1 b a c ore 

 available to the Japanese winter longline fishery 

 make a vertical migration in the spring and be- 

 come available to the Japanese s u m m e r pole- 

 and-line fishery. Horizontal distribution of 

 temperatures of the surface waters during the 

 winter appears to affect the migration of alba- 

 core from the longline fishery into the pole -and - 

 line fishery. The variations and persistence of 

 warm and cool water, winter to summer, are 

 primary criteria for predicting the location and 

 abundance of albacore available to the summer 

 fishery. 



To facilitate the prediction for the sum- 

 mer fishery, the patterns of temperature dis- 

 tribution for the periods January- June, 1951-58, 

 were classified into three types. In the first, 

 cool waters are found inshore, winter to summer. 

 The warm Kuroshio waters do not reach the main- 

 land. In the second, warm Kuroshio waters are 

 inshore with the cooler waters offshore during 

 the January-June period. In the third classifi- 

 cation, cool waters are inshore from January 

 to April or May and are then replaced by 

 warmer waters. 



In the first category, winter albacore are 

 found east or south of the inshore cold water. As 

 the spring and summer fishery begins, these fish, 

 which tend to migrate northward , are barred 

 from doing so by the cold water, and so move 

 rapidly eastward through the 18°-20° C. water. 

 These fish remain available to the pole-and-line 

 fleet during April and May and then move out of 

 the area of the fishery. 



In the second category (cold inshore water 

 lacking), winter albacore are found inmore west- 

 erly and northerly areas than in the first category. 

 Although the start of the summer season may be 

 delayed, good fishing may continue well into late 

 summer in areas close to land. 



In the third category (cold inshore water 

 is present until April, then d i s a p p e a r s ), the 

 winter fishery develops to the south and east, 

 although not to the extent observed in the first 

 category. Albacore remain west of longitude 

 140° E. until May, and the pole-and-line fishery 

 develops during May and June, relatively close 

 to land. 



Thus the knowledge of winter conditions 

 and the degree of persistence of these conditions 

 through the spring period provides a means for 

 determining the potential location and success 

 of the summer pole-and-line fishery. 



The location of the principal summer 

 fishing grounds, whether westerly and inshore 

 or easterly and offshore, results not only from 

 the oceanographic conditions in the area of the 

 summer fishery but also from the fluctuations 

 of oceanographic conditions of the previous win- 

 ter and the associated variations in the migration 

 of the albacore. The terms "environmental 

 resistance" and "environmental induction" were 

 proposed. Waters with temperatures below 

 16.3° C. impede or deflect the migration of alba- 

 core and thus are in the category of an environ - 

 mental resistance; those between 16° and 22 " C , 

 delimit the areas of migration and are termed 

 environmental inductance. Using 10-day sur - 

 face temperature charts for the period December 



25 



