Dolphins and Yellowfin Tuna

• In the eastern Pacific Ocean, it is common to see dolphins congregating above schools of yellowfin tuna. The dolphins and tuna swim together for thousands of miles, although no one is sure why. The habits were picked up by tuna fishers at sea, who realized that they could use the dolphins to locate tuna. This was far easier than keeping an eye out for tuna, as dolphins must surface regularly to breathe air.
  
  

Purse-Seine Fishing

• A common method of tuna fishing was to encircle large purse-seine nets around the dolphins--and, consequently, the schools of tuna. Purse-seine nets work by attaching weights to the bottom of the net, then submerging the net vertically. The top of the net floats on the surface while the rest dips deep into the water to catch fish.
  
  

Dolphin Deaths

• It became common for the dolphins to die of asphyxiation as the net closed over them. Since dolphins must surface regularly to breathe air, the died before the nets were retrieved. According to FORSEA Institute of Marine Science, approximately 4.8 million dolphins were killed between 1959 and 1972.
  
  

Activism

• By the early 1970s, according to scientist William Fox of the National Oceanic and Atmospheric Administration, hundreds of thousands of dolphins were dying each year as a result of tuna fishing. In response, Congress passed the Marine Mammal Protection Act of 1972, among the first legislative acts to broadly try to limit human impact on marine mammal populations, then the Dolphin Protection Consumer Information Act, which specifically addressed purse-seine fishing of tuna.
  
  

"Dolphin Safe" label

• For a can of tuna to obtain the U.S. Department of Commerce dolphin-safe label, no dolphins were to be killed or seriously injured, and a purse-seine net must not have been used on the fishing trip to encircle an area containing dolphins, even if no dolphins were actually killed. The Inter-American Tropical Tuna Commission estimates that the dolphin mortality rate was reduced from 132,000 in 1986 to less than 1,200 in 2008.