Before 1950 Commercial fishers catch tuna with pole and line.
Fishers discover that big yellowfin tuna swim under schools of dolphins.
1959 Fishers begin switch to purse seine nets. 1960s Up to 400,000 dolphins are crushed or drowned each year in purse seines. Ocean activists and consumers boycott canned tuna to protest the dolphin slaughter. The U.S. Congress passes the Marine Mammal Protection Act, which puts observers on tuna boats and makes U.S. boats change fishing methods to minimize dolphin kill. 1980s Foreign boats, which don't have to protect dolphins, take over most tuna fishing.