and Kazuo Fujino have discovered a number of methods to 

 identify genetic differences of several groups of skipjack 

 tuna. 



There exist, then, large, potentially harvestable stocks 

 of tunas in the central Pacific Ocean. But where in that 

 vast region are they to be found? Some evidence suggests 

 that the Hawaiians may not have to search very far to 

 locate these fish. The adjacent waters are very productive 

 of big tunas. Heavy catches of yellowfin tuna are made by 

 the Japane.se longliners within a few hundred miles of 

 Hawaii. 



In the most exhaustive review of the Japanese longline 

 fishery in the Pacific printed to date, Brian J. Rothschild 

 drew upon the data printed in the Japanese journal Tuna 

 Fishing to depict the expansion of the longline fleet in time 

 and space from 1953 through 1963. He was interested in 

 changes in large areas from year to year. He divided the 

 Pacific Ocean into 20 quadrangles, an area about 1,200 

 nautical miles to the side, and investigated the fishing history 

 of each. Most of his data deal with the yellowfin and bigeye 

 tunas, which dominate the Pacific longline catches. 



Rothschild documented the rapid spread to the east and 

 south of the center of longline fishing effort in the Pacific. 

 In 1953 it lay off the home i.slands of Japan; the farthest 

 east effort extended was a tentative probe to the northeast 

 of the Hawaiian Islands. In 1954 the Japanese fleet went 

 farther into the central Pacific. By 1955 it was fishing not 

 far from Baja California, and the following years saw effort 

 being expended from the coast of Asia to that of South 



America, as interest in the fishery moved south of the 

 Equator. By 1963, the principal center of effort of the 

 Japanese longline fleet lay nowhere near Japan, but in a 

 high-seas quadrangle in the eastern Pacific just south of the 

 Equator, a shift of several thousand miles in a decade. 



When compared with reported tuna catches and converted 

 into an index of abundance, these effort figures suggest that 

 throughout these years the big yellowfin tuna caught by the 

 longline have remained most abundant in the southwestern 

 Pacific, but that bigeye tuna have been more abundant in 

 the central and eastern Pacific ; Rothschild says that the 

 eastward expansion of the fishing was stimulated by the high 

 apparent abundance of bigeye tuna in the east. Is this 

 expansion paying off? Some scientists think it is not, point- 

 ing out the greater cost of catching bigeye tuna in the 

 eastern Pacific than to the west (because the distances to 

 home ports are longer). Rothschild believes that a con- 

 striction of the longline activities looms ahead. He sees 

 the concentration of effort falling back westward to the 

 vicinity of Hawaii. 



The four quadrangles which join near the Hawaiian Islands 

 have apijarently provided a substantial share of the Japanese 

 longline catch for the past several years. The southern pair 

 of quadrangles has usually exceeded the Pacific-wide average 

 for the yellowfin tuna catch. 



Thus substantial tuna resources are available in the central 

 Pacific to one of the two standard techniques of capture. 

 The question is: Where are the fish that are not taken by 

 this method ? 



26 



