Purse Seine boats encircling school of fish

The main way that tuna is caught is through purse seines in the Eastern Tropical Pacific. Basically, after a large group of tuna is located, a miles-across purse seine net is closed around them via a group of small boats associated with a large factory ship.

This technique is pretty standard- the main variation lies in how the large group of tuna is located. There are basically three ways to do this:

1) Get lucky and happen to stumble across a large group of tuna visible from the surface in the middle of an enormous ocean. Obviously, this isn’t terribly practical.

2) Attract tuna using floating objects. Stay tuned, we’ll come back to #2.

3) Follow dolphins, because dolphins in the Eastern Tropical Pacific are often associated with large schools of tuna. Dolphins are easy to follow because, unlike tuna, they have to come up for air.

As a result of pressure from environmental activist groups like Greenpeace, it became illegal to fish using method #3, and we now have what is called “dolphin safe tuna”. Technically this means only that the tuna isn’t harvested by searching for dolphins associated with a school of tuna, something that many environmental groups think isn’t a strong enough definition.

“Ten thousand sets of purse seine nets around immature tuna swimming under logs and other debris will cause the deaths of 25 dolphins; 130 million small tunas; 513,870 mahi mahi; 139,580 sharks; 118,660 wahoo; 30,050 rainbow runners; 12,680 other small fish; 6540 billfish; 2980 yellowtail; 200 other large fish; 1020 sea turtles; and 50 triggerfish.”

“Ten thousand sets of purse seine nets around mature yellowfin swimming in association with dolphins, will cause the deaths of 4000 dolphins (0.04 percent of a population that replenishes itself at the rate of two to six percent per year); 70,000 small tunas; 100 mahi mahi; 3 other small fish; 520 billfish; 30 other large fish; and 100 sea turtles. No sharks, no wahoo, no rainbow runners, no yellowtail, and no triggerfish and dramatic reductions in all other species but dolphins.”

Interesting article. So although almost 4000 cute lil dolphins are saved, the cost in other more endangered species, and juvenile tuna (hurting the fishery itself) is very much higher! And if accurate, perhaps too high to justify.

Read the full the article here and discuss.

Filed under: Conservation, Ryan McCardle