Fishing on Porpoise: The Origins of Dolphin Bycatch in the American Yellowfin Tuna Industry

Since the late 1950s, millions of dolphins have died as bycatch in the American yellowfin tuna industry. These deaths were not caused by accidental incidents between humans and dolphins, but rather were the result of a common fishing method used to catch yellowfin tuna that fishermen called “porpoise fishing” or “fishing on porpoise.” Although fishermen had caught tuna alongside dolphins since the 1930s, mass dolphin bycatch did not begin until the late 1950s, when the fleet converted from live-bait pole-and-line fishing to purse seining. This conversion—labeled the “purse-seine revolution”—occurred in response to economic and geopolitical pressures that threatened the future of the industry and was made possible by technological advancements that made purse seining a more effective method for catching yellowfin tuna. This conversion fundamentally altered the relationship between fishermen and dolphins. This article argues that the origins of mass dolphin bycatch are rooted in the purse-seine revolution and lie in the nexus of the economic, geopolitical, and technological developments that led to this conversion.