ty Z. Oka^Hma, former director of the Palaa riaheriee ■Experimental Station, and H. Nakamurn, 

 former technician of the Formosa Flsherlns Rxperlmental Station, Ijoth of whom carried on 

 research In the southern regions. 



2. Diagnostic Characteristics 



The yellowfln tuna (Figure 11) is characterized by a fusiform body with an elongated 

 caudal region. The oectoral fin extends beyond the origin of the set^ond dorsal. The second 

 dorsal and the anal fin are much elongated, and their lengths are extremely variable. Japa- 

 nese flehenr.en note a distinction between those yellcwfln tunac having longer fins (ito-shlbl) 

 and those having shorter fins (klhadamaguro). Nakamura (1939) pointed outi however, that 

 this Is not a racial or specific difference but an example of fins Increasing In length as 

 the size of the fish Increases. 



The yellowfln tuna Is nearly black on the back, and the sides are grayish with a 

 series of oblique transverse silvery white lines alternating with lines of similarly colored 

 dots. These markings tend to disappear in older fleh. The first dorsal and the pelvlcs xre 

 grayish and tinged with yellow; the tips of the second dorsal and the dorsal flnlets are 

 bright yellow; the pectorals are black on the inner side end grayish or sometimes yellow on 

 the outside; the anal and a^al flnlets are bright yellow. 



3. Distribution and Migration 



Japanese exploratory surveys and fishing operations by research and commercial 

 vessels show the yellowfln tuna to be widely distributed throughout the western Pacific Ocean 

 and the Indo-Paclflc region (Figure 12). The northernmost limit of the epeciee range in the 

 western Pacific ie usually about "^S^N latitude, but ooraelonally it extends past 40'^N latitude. 

 The yellowfln tuna sometimes enters the Sea of Ji^ian and has been recorded from Otaru, 

 Hokkaldot In late summer (Klehinouye, 1923, p 437). 



Catch records of tunas obtained by research and fishing vessels over a period of 

 11 years (1930-40) havo been compiled by Nakamura (1943). The d?.ta show that the yellow- 

 fin tuna not only is widely distributed through almost the entire tropioal southwest Pacific 

 and Indo-Paoiflc zones but also is the nost abundant of the giant pelagic fishes taken by 

 long line in those areas (Table 1). The average weight of the species in each locality is 

 also noted. 



A further analysis of thene data by seasons (Table 3) indicates that fishing condi- 

 tions for the tunas are, for the most part, goou throughout the year In almost the entire 

 tropical zone. A breakdown by eoecios is not possible since the i^tita are inconplete. 

 Differences in the amount of catch by seasons can be noted in several regions, the southern 

 coast of Sumatra, Timor Island, Celebes Sea, and the area east of the Philippine Islands. 

 The direction of the wind has much Influence on surface currents, and thus, according to 

 Japanese scientists, It affects the distribution and consequently the concentration of the 

 species. Nevertheless, even in those areas where seasonal variations occur and the catch 

 decreases markedly during a season, the number of tunas taken (except off Formosa and the 

 Philippine Islands) compares favorably with the three to four fish obtained per 100 hooks in 

 Japanese waters. 



An emalysls by latitudes of the catch of yellowfln tuna in the westom Pacific Ocean 

 Is possible from the catch statistics gathered by the Shonan Maru, a research vessel survey- 

 ing the areas east of the Philippine Islands and in the former Mandated Islands from July to 

 September 1937 (Table 3). During the months surveyed the catch was greatest in tropical 

 waters, particularly in the region* where the Equatorial Counter Current originates and flows, 

 and was less in the more northern latitudes. Comparable data on other seasons of the year 

 are not available, butt as noted (Table 2), evidence shows that shifts in the concentration 

 of the species may occur with changing seasonal conditions, 



Japanese scientists hpve no definite information regarding the migration path follow- 

 ed by the yellowfln tuna, but it is believed that during the spring, beginning about April, 

 certain segments of the populations in the southern regions break away and move northward, 

 over a wide areai into the temperate zona (Figure 12). The greatest concentrations, never- 

 theless, remain In the warm latitudes. The migratory yellowfln tunas are taken during the 



P-6307 



