STATUS OF THE FISHERY FOR TUNAS OF TROPICAL WATERS OF THE EASTERN PACIFIC 



by 



Milner B. Schaefer i/ 



GEOGRAPHICAL EXTENT OF THE FISHERY 



The fishery for the yellowfin and skipjack tunas of the Eastern Pacific extends 

 from California to Peru and Chile, and offshore for several hundred miles, encompassing 

 also the outlying islands — Revilla Gigedos, Clipperton, and Galapagos. The areas of fish- 

 ing and the relative yields obtained from them are illustrated in figures 1 and 2, which 

 show the catches logged by baitboats by 1° squares for the years 1956 and 1957. The chart 

 for 1956 represents a "normal" year when the fish are found in commercial concentrations 

 from about Cedros Islands (Baja California) to northern Peru. These are approximately 

 the limits of the water of suitable temperature for the tropical tunas at the northern and 

 southern extremes of their range. The fish apparently move away from the equator during 

 the summer and toward it during the winter, corresponding to the migration of the isotherms. 

 The chart for 1957, which was a warmer than normal year throughout the Eastern Pacific 

 indicates that in such a year the fish are found further to the north and south at the 

 extremes of their range. 



It appears that the fishery, at the 

 present time, encompasses the entire range 

 of these species along the coast of the 

 Americas. However, the tunas probably occur 

 further offshore than the present range of 

 the fishery, this being especially true of 

 skipjack. 



Although the purse-seine fleet operates 

 over roughly the same area as the baitboats, 

 the fishing by this gear tends to be more 

 concentrated in certain localities, includ- 

 ing the local banks off Baja California, the 

 Gulf of California, the Revilla Gigedo Is- 

 lands, and the region off the Gulf of Guaya- 

 quil, and along the coast of Peru. 



CHANGES IN THE FISHING FLEETS 



Table 1 (page 3ft) shows the numbers of 

 baitboats in the California fleet, by size 

 categories, for the years 1932-58, inclu- 

 sive. It may be seen that the fleet reached 



1/ Director of Investigations, Inter- 

 American Tropical Tuna Commission, 

 La Jolla, California. 



its peak in 1951 and has declined steadily 

 since that year. At the same time, there 

 has been a shift from small vessels to ves- 

 sels of larger capacity, particularly during 

 the years since the end of World War II. 



Number of vessels of the purse-seine 

 fleet, for the years 1931-58, by size cate- 

 gories, are shown in table 2 (page 39) . A 

 notable feature of this table is the sharp 

 increase in numbers of purse-seine vessels 

 in 19U5, 19U6, and 19U7, which was the 

 result of the diversion to the tuna fishery 

 of vessels which formerly had not fished 

 these species, in consequence of the failure 

 of the sardine fishery. It may be seen 

 that the purse-seine fleet reached a peak 

 in 19h8 and declined subsequently through 

 the year 1958. Part of the decline was due 

 to losses of vessels and transfer to foreign 

 countries, but a substantial share is also 

 due to the fact that some of the vessels 

 which had shifted from the sardine fishery 

 were not successful in the tuna fishery and, 

 therefore, abandoned attempts to fish tuna. 



In late 1958 and 1959, as a consequence 

 of very good success of fishing by purse 

 seiners during 1957 and 1958, several large 



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