Horizontal distribution of tuna larvae is 

 discussed with some mention of juveniles; how- 

 ever, these distributions are treated only quali- 

 tatively. In low latitudes between 10° N. and 

 10° S. , larvae seem to occur all year round, but 

 in higher latitudes they tend to occur in spring 

 and summer. Larvae of frigate mackerel (A. 

 tapeinosoma) also have a wide distribution, 

 however, their abundance is assumed to be high 

 in waters close to islands. Larvae of T. orien- 

 talis are taken in waters in the vicinity of Luzon 

 Island, Okinawa, and in the area to the north of 

 the Bonin Islands during May and June. They 

 are assumed to be abundant also in the area of the 

 Kuroshio Current. Most of the yellowfin (N. 

 macropterus) larvae are taken in tropical (equa- 

 torial) areas, and some are found in subtropical 

 areas which are under the influence of warm 

 currents. Larvae representing types A, taken 

 in July, and B, taken in December, are present 

 in the area between latitudes 10° N. and 25° N. 

 in the western Pacific. 



Larvae of all five istiophorid species 

 distributed in the Indo-Pacific areas are identi- 

 fied. Shortnosed spearfish (Tetrapturus 

 angustirostris Tanaka), sailfish ( Istiophorus 

 orientalis T. and S.), and striped marlin 

 (Makaira mitsukurii J. and S. ) are characterized 

 by a long snout, and black marlin (Eumakaira 

 nigra Nakamura) and white marlin (Marlina 

 marlina J. and H. ) are characterized by a short 

 snout. The former three species are distin- 

 guished from one another by the profile of t h e 

 head and the number of dorsal fin rays, while 

 the latter two species are distinguished from 

 each other by the shape of the pectoral and dor- 

 sal fins. 



Results of larval net hauls indicate that 

 both tuna and istiophorid larvae undergo vertical, 

 diurnal migration in the upper 50 meters of 

 water. 



Yabuta, Yoichi, and Mori Yukinawa 



Age and growth of yellowfin tuna. /Con- 

 ference Paper VII - 7.7 ( See also 

 Yabuta, Yoichi et al. Age and growth 

 of yellowfin tuna. Rept. Nankai Reg. 

 Fish. Res. Lab. no. 5, p. 127-133 

 (1957); no. 11, p. 77-87 (1959); no. 12, 

 p. 63-74 (I960).) 



Length frequency distributions of yellow- 

 fin tuna taken by pole and line and by longline in 

 waters adjacent to Japan were analyzed, and a 

 growth curve was obtained. The scale method 

 of age determination was also used to derive a 



growth curve. Tag recovery data substantiated 

 the results obtained by the other two methods. 



In the length frequency method, the 

 monthly modal mean lengths for each age class 

 were plotted for the years between 1953 and 1956, 

 and the progression in size was noted. Of scale 

 samples from 2, 087 fish examined in scale 

 studies, those from 1,204 (57.7 percent) were 

 unreadable. Unreadable scales, however, oc- 

 curred more frequently in larger fish. There 

 were 24 percent unreadable samples from fish 

 under 100 cm. in length, 68 percent from fish 

 between 101 cm. and 131 cm. , and 95 percent 

 from fish larger than 131 cm. Scale studies also 

 indicated that two rings are formed each year, 

 one in March and April and the other in Septem- 

 ber and October. 



In general, the growth rates estimated 

 by the length frequency method and the scale 

 method and from tagging data were in good agree- 

 ment with one another. The results showed 

 that the yellowfin is a relatively rapid-growing 

 tuna and that growth during the early stage of 

 life is particularly rapid. The first major group 

 of fish entering the commercial fishery (at about 

 50 cm. ) was estimated to be 1-year-old as deter- 

 mined by the scale method. 



Yamanaka, Hajime, and Noboru Anraku 



Relation between the distribution of tunas 

 and water masses of the North and 

 South Pacific Oceans west of 160° W. 

 /"Conference Paper V - 57 



A detailed examination of temperature 

 and chlorinity in the Pacific west of 160° W. , 

 and in particular of temperature-chlorinity 

 relationships in the upper 200 meters, suggests 

 that the surface water layers can be divided into 

 a series of types having characteristic ranges 

 of temperature and chlorinity. The observations 

 are grouped into (Northern Hemisphere) winter 

 and summer classes, and the water types given 

 preliminary designations based upon the current 

 system which dominates the area in which each 

 occurs. Thus, for example, there is a type O 

 surface water, in the region of the Oyashio, 

 which is associated with the underlying Sub- 

 Arctic water mass, there are types K and N, 

 representing the Kuroshio and North Equatorial 

 Current surface water types which overlie the 

 Western North Pacific Central water mass, and 

 there are water types associated with the 

 Countercurrent, equatorial waters, the South 

 Equatorial Current, the Coral Sea, the Central 

 and southwest Tasman Sea areas, and the Sub- 

 Antarctic. 



