The Tuna-Dolphin Issue 
For reasons not fully understood, schools of large 
yellowfin tuna (those greater than 25 kilograms) tend 
to associate with dolphin schools in the eastern 
tropical Pacific Ocean, an area of more than five 
million square miles stretching from southern Califor- 
nia to Chile and westward to Hawaii. In the late 
1950s U.S. fishermen began to exploit this association 
by deploying large purse seine nets around the more 
readily observed dolphin schools to catch the tuna 
swimming below. Despite efforts by the fishermen to 
release the encircled dolphins, some become trapped 
in the nets and drown. As discussed below, efforts to 
reduce the incidental mortality of dolphins in this 
fishery have been a central focus of the Marine 
Mammal Protection Act since it was enacted in 1972. 
Background 
At its peak in the mid-1970s a U.S. fleet of more 
than 150 vessels accounted for nearly 70 percent of 
the fishing capacity in the eastern tropical Pacific tuna 
fishery. In the late 1970s and early 1980s, the U.S. 
fleet declined and the number of foreign vessels 
participating in the fishery grew. As discussed in 
previous annual reports, by 1990 only 30 U.S. tuna 
vessels remained in the fishery, accounting for less 
than one-third of the total fleet capacity. 
On 12 April 1990 the three largest U.S. tuna 
canners announced that they would no longer purchase 
tuna caught in association with dolphins. In response, 
there has been a further decline in U.S. purse seine 
vessels fishing in the eastern tropical Pacific. During 
1992 only seven U.S. vessels fished for tuna in the 
eastern tropical Pacific, and of these only five fished 
for tuna by setting on dolphins. 
Despite the decline of the U.S. tuna purse seine 
fleet, the United States remains an important market 
for tuna caught in the eastern tropical Pacific. Prior 
to the announcement by U.S. canners of their “dol- 
phin-safe” purchasing policy, about 44 percent of tuna 
caught in the eastern tropical Pacific was sold in the 
United States, about 30 percent in Latin America, 
about 20 percent in western Europe, and about 5 
percent in Asia. Although the full extent of any 
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Chapter IV — Marine Mammal-Fisheries Interactions 
market shift that may have resulted from the “dolphin- 
safe” policy of U.S. canners is unknown, it is be- 
lieved that the U.S. market for eastern tropical Pacific 
tuna has declined since April 1990. 
The decline of the U.S. fleet in the 1970s and 
1980s has been offset in large part by growth of 
foreign fleets in the area. The Mexican fleet in- 
creased by nearly 50 percent during the 1980s and 
displaced the U.S. fleet as the primary participant in 
the fishery. The Venezuelan fleet more than tripled 
in size during the 1980s and now has about 20 vessels 
participating in the fishery. The other major partici- 
pants in the eastern tropical Pacific tuna fishery are 
Vanuatu and Ecuador. Ecuador’s vessels, however, 
currently do not fish for tuna by setting on dolphins. 
A parallel shift also has occurred in the tuna 
canning industry. During the early years of the 
fishery, most of the tuna canning industry was 
operated by U.S. companies. In the 1960s, 12 tuna 
canneries were in operation in southern California, 
others were located on both coasts of the United 
States, two were operating in American Samoa, and 
two in Puerto Rico. Today only two canneries, both 
in southern California, remain in operation in the 
United States. Three canneries are operating in 
Puerto Rico, and two in American Samoa. The 
country with the most dramatic increase in canned 
tuna production during the past decade is Thailand, 
which began canning tuna in the early 1980s and now 
is one of the world’s largest producers. Other nations 
that substantially increased canned tuna production 
during the 1980s are Italy, France, Mexico, the 
Philippines, and Céte d’Ivoire. More recently, there 
has been considerable growth in Indonesia’s tuna 
canning industry. 
As the eastern tropical Pacific tuna fishery shifted 
to foreign control, so did the incidental dolphin 
mortality. Recognizing this, Congress amended the 
Marine Mammal Protection Act in 1984 to require 
that foreign nations exporting yellowfin tuna to the 
United States adopt dolphin-saving programs equiva- 
lent to the U.S. program and achieve an incidental 
mortality rate comparable to that of the U.S. fleet. 
The Act was further amended in 1988 to specify what 
would constitute an acceptable foreign program and a 
comparable mortality rate. Recent efforts, including 
