p.nd migration pathe In the westarn Pacific Ocean. The following Ir.fDrmation i» based on 

 fragmentary material presented In various scientific Joumale, augmented by reports sab- 

 mltted by flehlng and reaearch vessels. 



JCvldenoe, based on fishing areas, density of the populations In different regions, 

 and the months of the year in which the species generally appears in different localities. 

 Indicates that two major groups of skipjacks migrate into Japanese waters (Figure 5). 



One group, which fishermen believe orglnates in the Celeb»s and Molucca seas, 

 proceeds northward along the Philippine Islands and enters the waters of the Ryukyus. 

 Skipjacks are present in the ^rukyu waters throughout the year. Weather conditions, how- 

 ever, make fishing operations imposElble in January. Two types of fish are taken in these 

 waters: rasident schools, which are fished principally in the areas around the small is- 

 lands and on shallow banks; and migratory shoals, which are found in any part of the region, 

 although usually they are taken in the open sea over deep water. The migratory fish are 

 distinguished from the nonir.igratory forms by their relatively heavier bodies. They com- 

 prise about 60 percent of the total catch in the Eyukyus (Alkawa, 1937, pp 17-21). In the 

 early spring the migratory shoals move northward and between April and June appear off Japan 

 in the vicinity of Shizuoka «uid Kanagawa prefectures, east central Honshu, A few schools 

 occasionally enter the Sea of Japan, and skipjacks are taken there In small noinbera in late 

 autuain or early winter (Klshlnouye, 1923, p 454). 



The other group of skipjacks, which It is believed originates In the area of the 

 former Mandated Islands and New Guinea, moves northward through the Marianas and Bonin is- 

 land chains. Members of this group are present in Bonin waters at all seasons of the year, 

 but fishing operations are not carrlfld on In January and February becauso of unfavorable 

 weather conditions. This group also consists of resident and migratory populations. 

 During the spring the migratory schools move northwaird into Jeqpanose waters and meat the 

 shoals advancing from the Byukyus. 



The large concentrations of skipjacks advancing along the Pacific coast of Japan 

 reach the area off the northeastern coast of Honshu, known as the Tohoka sea region, by 

 late summer. When oceanographic conditions are favorable the shoals occstelonally advance 

 to Itrap and Shlkotan islands in the Kuril Islands. In an analysis of the skipjack schools 

 appearing in the Tohoku sea region during 1934 and 1935. Aikawa (1937, p 21) presented evi- 

 dence that they were composed of 60 percent Syukyu and 20 percent Bonin stock. 



Slclpjaoks entering Japanese waters during the summer are sexually Immature. It 

 Is quite evident that they migrate northward solely for the purpose of feeding. The average 

 weight of the Individuals landed is about four kilograms. The maxlmam weight obtained rare- 

 ly exceeds eight kilograms (Tamamoto, 1942, pp 138-139). 



Oaually the skipjaok migrates as far north as 43<^H latitude and then returns south 

 to about 40'^. During late September and October the fish begin to disappear and are no 

 longer seen at the surface. Tho direction of migration is not definitely known, but during 

 late fall and winter months tuna boats operating long lines in the mid-I-aciflo region have 

 taken skipjacks swimming in deep waters. It may be inferred that the fish are moving either 

 directly east or southeast. 



Some workers claim that the species performs one great migration covering the whole 

 area of the Paelfle. To support this contention they cite the fact that large schools of 

 fully mature Individuals have been eeuxght from Hay through July In the region where the 

 Counter Equatorial Current passes through the former Mandated Isleuds (Ceo-ollne, Marshall, 

 ami Palau groups). These fish are seen approaching from the east. Other biologists main- 

 tain that several races of skipjacks exist • eaich peculiar to a different locality emd each 

 making feeding and spawning migrations of its own. Neither school of thought has been able 

 to supply factual data to establish its contention. 



The fishing grounds for the skipjack in the southern regions are not truly Indic- 

 ative of Its distribution (Figure 6). Fishing operations for the species were of a local 

 nature, carried on by small companies located at selected Island bases. According to 

 T. Hakayama, skipjack expert for the Japanese Tuna Fishermen's Assoolatloni the apecles Is 



15 



P-6307 



