154 EIGHTH PACIFIC SCIENCE CONGRESS 



estimate at this time, in the absence of adequate information on the 

 distribution and biology of fish involved. 



Yellowfin 



The yellowfin tuna (Neothunnus macropterus) is a tropical species 

 occurring everywhere in Pacific equatorial waters between approx- 

 imately, the surface isotherms of 18 °C. It is the object of a large 

 fishery on both sides of the Pacific Ocean and in the Central Pacific 

 westward of the International Date Line. Considerable stocks, not now 

 exploited, are known to exist in the eastern equatorial Pacific between 

 the International Date Line and the presently fished seas adjacent to 

 the American West Coast. 



As noted previously, the fishery for the tropical tuna? began in 

 California shortly after the initiation of fishing for albacore. The sea- 

 sonal and erratic nature of the albacore fishery led the fishermen and 

 canners to turn to the tropical yellowfin and skipjack tunas. The 

 fishery began as a seasonal one in waters of Southern California and 

 Northern Baja California, but the fishermen soon learned that by going 

 farther south yellowfin and skipjack could be taken during a greater 

 part of the year, more regularly, and in greater abundance. This 

 stimulated the building of large vessels which could stay at sea longer 

 and range further from port. The failure of the albacore fishery in 

 1926 gave strong impetus to the expansion of the tropical tuna fishery. 

 By 1930 vessels were fishing regularly far down the Mexican coast, and 

 beginning to venture even farther south. 



As the vessels ventured further into the tropics on longer voyages, 

 problems of preserving the catch multiplied. During the 1930's ex- 

 periments were made with mechanical refrigeration, and finally brine 

 freezing of the fish was developed. At the same time, the vessels evolved 

 into large craft of the high seas capable of operating thousands of miles 

 from home on long voyages. By 1938 vessels from California ports were 

 operating over the entire area from Southern California to Ecuador, 

 and offshore over 200 miles. The outbreak of World War II curtailed 

 sharply the long range fishing, because many of the larger vessels were 

 converted to military duty and various restrictions were placed on the 

 operations of the remaining vessels. With the cessation of hostilities, 

 however, the fleet again grew rapidly and prosecuted the fishing even 

 more vigorously. The long range fishery has been extended to northern 

 Peru, and provides now an even greater share of the catch than before 

 the war. 



This fishery by United States vessels produces by far the major 

 part, over 90%, of the catch of yellowfin, as well as of skipjack, tuna 

 taken in the Eastern Pacific. Small local fisheries developed during 



