Saturday, September 19, 2009

Do You Know What "Dolphin-Safe" Means?

Dolphin-safe logoAaaagh! Another example of the law of unintended consequences.

Read all about it in The Ecological Disaster That Is Dolphin-Safe Tuna on Southern Fried Science. It's written by Dave Shiffman, a marine biology grad student who goes by the name WhySharksMatter. (via

To summarize, the practice of commercial tuna fishing is based on catching large groups of mature tuna all at once in a "purse seine net," controlled by a bunch of small boats that work with a larger parent ship. There are two ways to find a large group of tuna:

  1. Find a group of dolphins (when they come up for air) and you will often find a large group of tuna, because for some reason, dolphins follow tuna.
  2. Put a floating object on the ocean surface. This will attract large groups of tuna, as well as large groups of many other ocean species. Then catch the tuna (and a lot of "bycatch" of the other species at the same time, including dolphins and immature tuna).
Tuna fishermen traditionally used the first method, but, as we all remember, there was an outcry a number of years ago about how many dolphins are killed while catching tuna, so that method has been abandoned in favor of the second option, which is marketed as "dolphin-safe tuna."

Here's the key point, though: it's not actually dolphin-safe, and and it's even less safe for the other species in the vicinity. Quoting from the article, these are the comparative results of the two methods:
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.
The article goes on to point out that while dolphins are not an endangered or threatened species, many of the others caught with the floating object method are, such as sea turtles and sharks. (See the recent coverage of damage to shark populations from fishing specifically for their fins, often discarding the rest of the animal.)

The article concludes with these thoughts about dolphin-safe tuna:
this is a classic example of the false value our society places on marine mammals.... I think to wipe out the populations of so many other species in order to save a few individual dolphins (recall, dolphin populations aren’t threatened by dolphin-associated fishing, though lots die) is ludicrous.

I think we should go back to fishing dolphin-associated sets AS SOON AS POSSIBLE and hope that the damage done to shark, seabird, sea turtle, and large fish populations by the dolphin-safe disaster is fixable.
Of course, all of this begs the question of whether tuna fishing and tuna consumption in general can be sustainable. Blue fin tuna, for instance (used in sushi), is on the brink of extinction. From what I've read, yellow fin tuna is on the ropes in some fisheries, but not overall. Giving up tuna (like the argument for giving up or substantially decreasing consumption of meat in general) is an important step toward fashioning a more sustainable way of eating.

Footnote: Dave Shiffman was on public radio in July to discuss this issue, debating someone from the Earth Island Institute, who was advocating dolphin-safe methods as the best solution. Shiffman also wrote a follow-up piece about that conversation. It all goes to show how complicated it can be to make positive environmental changes.

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