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Dolphin-safe tuna: conservation success story or ecological disaster?




The commonly believed narrative about dolphin-safe tuna goes something like this: Lots of dolphins were being killed by tuna fishermen, outraged environmentalists led a massive PR campaign, legions of adorable children wrote to their elected officials, elected officials changed the rules to protect dolphins, and everything is better now. Hooray, we saved an innocent species and helped the environment!

That narrative is a great story. It shows that if a few people who care can convince others that their cause is just, there’s no limit to what we can accomplish. It’s inspiring. Too bad it’s not really true. As it turns out, we made things worse- a LOT worse.

Before we get into specifics, a little background  is in order. The tuna fishery, one of the world’s largest, employs tens of thousands of people and provides millions with a cheap source of protein. It can be difficult for people who have never seen it in action to appreciate the scale of modern commercial fisheries. Commercial fishermen aren’t out on the high seas with handheld rods and reels catching one fish at a time. The nets that tuna fishermen use, which are called purse seines, are miles long. With a net that size, it’s pretty much impossible to catch only tuna. Those nets also catch anything that happens to be swimming near the tuna. These unfortunate animals, killed for being in the wrong place at the wrong time, are called bycatch.

The diagram below shows how tuna purse seine nets work. Once a school of tuna is located (we’ll discuss how that happens a little later), a series of support ships help to deploy the giant purse seine from the main factory ship. The bottom of the net is drawn closed, and the contents of the net (tuna and bycatch) are brought onto the main factory ship.

Figure from "An introduction to monitoring, control and surveillance systems for capture fisheries", available at FAO.org

Once the tuna are located, the method for catching them is just as I’ve described above. The differences, and the source of the controversy with tuna fishing, comes from how the tuna are located in the first place.

There are three ways that tuna schools can be located. The first is to search for them directly using surface ships and small aircraft, which is inefficient, time-consuming, and not always effective (you can’t see tuna from the surface if they’re deep enough or if weather conditions aren’t ideal). The second is to attract tuna using floating objects, which we’ll discuss in more detail shortly. The third is to follow dolphins- for unknown reasons, dolphins in the Eastern Tropical Pacific are often found associated with schools of large tuna.

Now that we have some background, let’s return to the “environmentalists saved dolphins from fishermen” narrative. The first part of the narrative is  mostly true. Because finding dolphin-associated schools of tuna was extremely easy (unlike tuna, dolphins have to return to the surface where they are easy to  spot), it was the preferred method for decades. The Eastern Tropical Pacific Tuna Fishery had a high rate of dolphin bycatch. According to NOAA’s Southwest Fisheries Service Center, an estimated six million dolphins were killed during the forty or so years that purse seining around dolphin-associated tuna schools took place. That’s approximately 150,000 dolphins per year, which is by far the largest cetacean bycatch of any fishery in history. However, it is important to note that mortality from being tuna bycatch did not mean that dolphins were endangered. The two primary species involved are spinner dolphins (data deficient) and spotted dolphins (least concern).

The second part of the narrative is also true. A massive PR campaign led by the Earth Island Institute resulted in making it illegal to sell tuna caught from dolphin-associated schools in the United States. Dolphin-safe tuna was born.

Now that fishermen could no longer use what was previously the most common method for catching tuna, they needed to change strategies. They turned to using floating objects (sometimes called FAD’s or fish aggregating devices) to attract tuna to a known location. One of the strangest known behaviors exhibited by open-ocean animals is their tendency to aggregate around any solid object that floats. This might have something to do with the fact that many open-ocean animals go their entire lives without seeing any sort of hard surface. This method is extremely effective for aggregating tuna, but it also aggregates many other species. Setting a purse seine around a dolphin-associated tuna school results in catching primarily large adult tuna (the target size because they have more meat per unit effort and because they have reproduced already) and dolphins (which are not endangered) . Setting a purse seine around a floating object results in all sorts of bycatch, including endangered sea turtles, open ocean shark species which are already in serious trouble, and high numbers of small tuna (which have not yet reproduced).

Table from Hall 1998. "Log" = floating object, "school" = tuna found by plane or boat, "dolphin" = dolphin associated

A simple glance at the table above shows that while dolphins bycatch goes down, every other studied species (except “unidentified bony fishes”, “other sailfishes”, and marlins) has much higher bycatch rates in “floating object” tuna fishing than in “dolphin associated” tuna fishing. In other words, while better for dolphins, “dolphin-safe” tuna is disastrous for almost everything else. For open-ocean sharks, floating object fishing is orders of magnitude worse than dolphin-associated fishing. In some cases, such as mahi-mahi, wahoo, and triggerfish, the new method is exponentially worse.

Large numbers of these already threatened sharks are killed by "dolphin-safe" tuna fishing

If you do the math on this (and you don’t have to because the Environmental Justice Foundation already did), you find that one saved dolphin costs 25,824 small tuna, 382 mahi-mahi, 188 wahoo, 82 yellowtail and other large fish, 27 sharks and rays, 1 billfish, 1,193 triggerfish and other small fish, and 0.06 sea turtles.

You and I can argue about the relative value of dolphins vs. triggerfish all day, but the important take-home message here is that we are protecting animals that are not endangered at the expense of dozens of other species, and some of those other species are endangered.

Last summer, I went on NPR’s “The Pat Morrison Show” to discuss this issue with a representative from the Earth Island Institute, the organization most responsible for dolphin-safe tuna policies. I had expected him to acknowledge that the bycatch was a problem, but that it was still important to protect dolphins because they’re intelligent mammals (or something like that). Instead, he argued that there was no bycatch of endangered species taking place under dolphin safe tuna policies, and he accused me of perpetuating the propaganda of evil fishermen who “just want to kill dolphins”. Yikes. His ridiculous rants (and his subsequent refusal to continue the discussion on Southern Fried Science) cost the Earth Island Institute my respect, as well as that of many who heard the interview.

The fight to save the oceans is a long and difficult one, and I don’t know for sure how we’re going to win. I do know, however, that we will never win by making up lies about the other side or refusing to acknowledge when we make mistakes. Let us be honest with ourselves and with the world- the push for dolphin-safe tuna was a mistake. It was a well intentioned mistake, but it was a big mistake with disastrous consequences.

What can we do? The first thing that popped into your head was probably “ban tuna fishing”, which is a more politically correct way of saying “make it impossible for the world’s poor to have healthy balanced diets”. It’s just not feasible to ban purse seine fishing. If you’re interested in helping by “voting with your wallet”, you can support sustainably-caught tuna, which is caught with a rod and reel and has almost no bycatch, but this method makes tuna so much more expensive that it’s not a large-scale solution.

A conscious choice to go back to a previously-banned fishing method that kills large numbers of charismatic animals puts a bad taste in my mouth, but the fact is that fishing for dolphin-associated schools of tuna catches primarily non-endangered dolphins and adult tuna. Dolphin-safe tuna fishing is killing dozens of species, many of whom are endangered, and threatening the integrity of entire ecosystems. The old way may be the better of two bad choices.

This is a modified repost of “the ecological disaster that is dolphin-safe tuna” from the old site. That award-winning post and it’s over 200 comments can be seen here.


Au, DW (1991). Polyspecific nature of tuna schools: Shark, dolphin, and seabird associates Fishery Bulletin

Barker, M., & Schluessel, V. (2005). Managing global shark fisheries: suggestions for prioritizing management strategies Aquatic Conservation: Marine and Freshwater Ecosystems, 15 (4), 325-347 DOI: 10.1002/aqc.660

Girard, C. (2004). FAD: Fish Aggregating Device or Fish Attracting Device? A new analysis of yellowfin tuna movements around floating objects Animal Behaviour, 67 (2), 319-326 DOI: 10.1016/j.anbehav.2003.07.007

Hall, M. (1998). An ecological view of the tuna-dolphin problem: Impacts and trade-offs Reviews in Fish Biology and Fisheries, 1-34

Joseph, J. (1994). The tuna-dolphin controversy in the eastern pacific ocean: Biological, economic, and political impacts Ocean Development & International Law, 25 (1), 1-30 DOI: 10.1080/00908329409546023

LEWISON, R., CROWDER, L., READ, A., & FREEMAN, S. (2004). Understanding impacts of fisheries bycatch on marine megafauna Trends in Ecology & Evolution, 19 (11), 598-604 DOI: 10.1016/j.tree.2004.09.004