Yellowfin tuna are found throughout the tropical Pacific. The world's single largest biomass of yellowfin inhabits the Eastern Tropical Pacific Ocean (ETP), ranging from Chile to southern California. Tagging studies indicate that the ETP stock is a single population, with seasonal coastal migrations but no large-scale movement to the central or western Pacific. In the daytime, mature yellowfin associate with dolphins to some degree in all the world oceans. However, the relationship with dolphins is well-developed in the eastern Pacific. ETP tuna stocks have been regulated by the Inter-American Tropical Tuna Commission since 1966.
Tuna was first canned in California in 1903; by 1907 the industry was well established, packing primarily albacore. By the late 1920's, the volume had shifted to yellowfin and the smaller skipjack. The development of brine refrigeration in the late 1930's led to the fishery's expansion far southward. In 1957, the introduction of strong, light-weight nylon netting and the power block spurred the traditional bait boat fleet to convert to purse seines, a more efficient and effective way to catch tuna.
The U.S. tuna fleet based in southern California grew to become the largest of its kind in the world. From 1982 through 1984, the major canneries in southern California relocated outside the U.S., unable to compete with foreign labor rates and increasing competition from imported, lower-priced water-packed tuna. The relocation of industry, and increasingly rigid marine mammal protection policies, are primary reasons why most U.S. tuna vessels now fish in the Western Pacific (many vessels also were forced to reflag or went bankrupt). California's tuna fleet is now a distant-water fleet that delivers its catch to canneries in Asia, American Samoa, South America and Puerto Rico
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