DEVELOPMENT AND CONSERVATION OF TUNA FISHERIES 155 



the 1920's and 1930's in Mexico and Costa Rica. During the war, with 

 the increased demand for tuna in the United States, a local fishery was 

 started in Peru for yellowfin and skipjack tunas, and this continues to be 

 an important part of the Peruvian fishing industry, greatly exceeded 

 in production, however, by the fishery for bonito. Recently a small 

 local fishery has been initiated in Ecuador. 



The giowth of the production of yellowfin tuna from the Eastern 

 Pacific is illustrated in Figure 1, in which the production of skipjack 

 is also depicted. These two tropical tunas are taken in the same waters 

 on the same voyages. The very rapid postwar growth of the fishery is 

 evident from this chart. There is evidence that the production of yel- 

 lowfin is no longer increasing, but the upward trend of skipjack produc- 

 tion is being maintained. 



Over 75% of the yellowfin and skipjack tunas taken in the Eastern 

 Pacific are captured by means of pole and line, live bait being employed 

 to chum the tunas to the vessel and to induce them to strike the lures. 

 Bait fishes are several species of small fishes, mostly of the families Clu- 

 peidae and Engraulidae, captured in the territorial waters of the several 

 countries bordering on the Eastern Pacific. The remainder of the catch 

 is made by means of purse seines. These methods capture only the 

 surface-schooling component of the population. No commercial fishery 

 has been developed for the large, old yellowfin tuna, analogous to the 

 Japanese and Hawaiian long-line fisheries. 



A parallel, but geographically even more extensive, development 

 of the yellowfin tuna fishery has taken place in the Western Pacific 

 Ocean. Yellowfin tuna occur during the summer months in Japanese 

 home waters, and for many years have been fished there by nets, long- 

 lines, and pole and line, but did not contribute an important share of 

 the tuna catch until the southward expansion of the 1930's. 



Surveys by government vessels and commercial companies, about 

 1931, discovered that yellowfin tuna and bigeye tuna (Parathunnus sihi) 

 are distributed throughout the tropical southwest Pacific, and can be 

 taken commercially in sub-surface waters of the high seas by means of 

 long-lines. This led to the initiation of a commercial fishery which 

 was, of course, very soon terminated by World War II. Immediately 

 following the war, the Japanese fishery expanded back into this area 

 as rapidly as permitted by the Occupation authorities. This fishery is 

 still expanding, and at the present time operates throughout the tropical 

 western Pacific as far east as the Phoenix Islands and south to the Coral 

 Sea, Arafura Sea and Banda Sea. This long-line fishery captures, in 

 addition to yellowfin tuna, quantities of bigeye tuna, spearfishes, and 

 sharks. The tunas captured by this mieans are mostly very large fish, 

 a good deal larger than those taken at the surface. Available recent 



