helicopters. Purse seining for yellowfin tuna became highly controversial in the late 1970s when it became apparent that the eastern Pacific fishery was killing many spinner dolphins, pantropical spotted dolphins, and other cetaceans (often called "porpoises" by the tuna fleet) that accompany the fish. This association has been long-recognized by commercial tuna fishermen. Dolphin-friendly labeling Since the introduction of "dolphin-friendly" labeling, an increasing number of purse seine sets are now made on "free schools" unassociated with dolphins, as well as schools that associate with floating objects—another long-understood association that has grown in importance in tuna fisheries. The latter practice in particular has a major ecological impact because of the high proportion of bycatch, including manta rays, sea turtles, pelagic sharks, billfish, and other threatened marine species taken by setting nets around logs and other floating objects. Such tuna are often significantly smaller than the larger adult tuna associated with dolphins. The removal of huge numbers of juvenile yellowfin and bigeye tuna that have yet to reach breeding age has major potential consequences for tuna stocks worldwide. Longline Most of the commercial catch is canned, but the sashimi marketplace adds significant demand for high-quality fish. This market is primarily supplied by industrial tuna longline vessels. Industrial longlining was primarily perfected by Japanese fishermen who expanded into new grounds in the Western Pacific, Indian, and Atlantic Oceans in the late 1950s and early 1960s. Longlining has since been adopted by other fishermen, most notably South Korea, Taiwan, and the United States. Tuna longlining targets larger sashimi-grade fish around and up that swim deeper in the water column. In tropical and warm temperate areas, the more valuable bigeyes are often the main target, but significant effort is also directed towards larger yellowfins. Longlining seeks areas of higher ocean productivity indicated by temperature and chlorophyll fronts formed by upwellings, ocean current eddies, and major bathymetric features. Satellite imaging technology is the primary tool for locating these dynamic and constantly changing ocean areas. Bycatch is a major environmental issue in the longline fishery, especially impacting billfish, sea turtles, pelagic sharks, and seabirds. Artisanal fisheries Besides the large-scale industrial purse seine and longline fisheries, yellowfin tuna also support smaller-scale artisanal fisheries that have often supplied local domestic markets for generations. Artisanal fisheries now also often fish for the lucrative sashimi market in many locations where international air shipment is possible. Artisanal fishermen tend to employ assorted