San José, Costa Rica, since 1956

Tuna Fishing Endangers Dolphins

Dolphins are Costa Rica’s most famous divers – and they have a problem. For decades, in the eastern tropical Pacific, the commercial fishing industry has hunted dolphin species that form enormous congregations, such as pantropical spotted, spinner, bottlenose, common and Risso’s dolphins.

Tuna always school beneath large groups of dolphins, so corralling the dolphins with helicopters and speedboats causes the tuna to form a more easily netted mass below. Unlike most sport fishers who catch a few fish in a sustainable way, many commercial operations set vast nets around dolphins in hopes of grabbing all the tuna possible. This technique has killed millions of dolphins, and continues to kill them as recently as last month off the Southern Zone’s Osa Peninsula.

Dolphin and tuna are often about the same size, and eat the same size of prey. The vast groups of yellowfin tuna constantly following large dolphin groups are led to lunch. The tuna seem to instinctively follow the dolphins, as do birds and other fish, because dolphins will find the food. The big brains of these marine mammals figure to look for chow a few miles offshore of an island, when the tide is high, the moon is full, the wind is clam, the water temperature is just right and the coast is clear, and the needlefish are schooling. The tiny brain of the tuna might just think: follow the dolphin.

Dolphins, being so social and traveling in such large groups, actually create a sort of structure, like a reef, in which smaller fish can hide as well as collect scrapes. Many species of fish, besides tuna, cruise in groups with the dolphins, including silky sharks, blue marlin and sailfish.

We call this famous phenomenon the tuna-dolphin association of the eastern tropical Pacific, not because it’s just tuna and dolphins but because huge commercial fishing fleets use dolphins breathing at the surface to find the tuna swimming below them. Many different species die in the nets of commercial fishing fleets. You may have heard of “dolphin-safe tuna”; this catchy phrase is better described as “some dead dolphin and mixed-species tuna.” The aforementioned catching method, sometimes still used, is “major dead dolphin and mixed species tuna.” As far as I know, none of the forms of massive-scale tuna fishing is even remotely safe for dolphins – some ways just kill less than others do.So, how do the methods differ? One is called a “backdown.” After netting all the tuna and dolphins through the normal process, the ship motors slowly in reverse. This, with the help of a few speedboats, lowers a part of the net down below the surface. Hopefully, the freaked-out dolphins will then swim out. Sometimes they do. Sometimes boats chase them out. But if the tuna follow them, the net is quickly yanked up. All the while, daylight is fading, the crew and workers are on the clock, and fuel is being guzzled. This is “dolphin-safe” tuna. Other methods don’t even use a backdown.

Waiting to catch the tuna when they are away from dolphins requires more time, effort and money, but is the only way to ensure dolphins are safe from slaughter. Reportedly, some boats do not set on dolphins, but until tuna consumers make this distinction, the prices of unscrupulous competitors will hurt the real “dolphin-safe” businesses.

Dolphin tourism can sometimes be at odds with commercial fishing interests. It makes it a little harder to surround a group of dolphins with helicopters, speedboats and a factory ship when a happy group of photosnapping tourists is in the way. On rare occasions, frustrated pilots in rickety helicopters that look more like lawn mowers than aircraft will attempt to drive off the people by buzzing a tourist boat near dolphins. If you are rooting for the dolphins, you can stay with them until there is not enough daylight for the time-consuming process of chasing and netting.

Why don’t the dolphins just smack a few boat captains on the head as they jump over the nets and swim away giggling? Because, like humans, dolphins, once they start to panic, are not so smart. Ancient instincts, such as freaking out, take over. And, as with humans, being in large groups makes panic worse. Dolphins are used to vast spaces; a net causes panic, and they just don’t think to jump over.

I wonder how commercial fishers will fare once the big pods are gone. This may sound distressingly familiar if you know about the vast herds or flocks of animals, such as American bison and passenger pigeons, which have disappeared on land and in the air. As the buffalo once did, the dead dolphins rot in waste or fall to scavengers, and, as with the passenger pigeons, a point may arrive when the population crashes suddenly to extinction.

Hopefully, Costa Rica will take as much interest in the people fishing around dolphins as it does in the tourists who come to see them. If so, perhaps the country’s dolphins can keep on diving.


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