IRA FLATOW: This is Science Friday. I’m Ira Flatow. This next story is about the world’s most popular fish. Here’s a little hint.

SPEAKER: Sorry, Charlie. Only the best tuna get to be Starkist. Insist on Starkist. Tell them Charlie sent you.

IRA FLATOW: That’s the famous Charlie the Tuna commercial from back in the day when Americans were getting their feet wet over tuna fish sandwiches, tuna noodle casseroles, all things made from canned albacore tuna. Fast forward to the more chic way to eat tuna– sliced into tiny pieces rolled into sushi with the pricier and meaty red raw bluefin tuna.

But don’t let those tiny sashimi slices fool you. Do you know how big a tuna is? Bluefin tuna are colossal. On average, they’re about 500 pounds. And the biggest one ever caught was a whopping 1,500 pounds. My next guest has me hooked on learning more about the surprising science of tuna and the history of how they became the world’s most popular fish– Karen Pinchin, science journalist and author of the new book, Kings of Their Own Ocean: Tuna, Obsession, and the Future of our Seas. She’s based in Halifax, Nova Scotia. Welcome to Science Friday.

KAREN PINCHIN: Thanks for having me on, Ira.

IRA FLATOW: Nice to have you on. Let’s start with some basics. Describe for me what a bluefin tuna looks like.

KAREN PINCHIN: So imagine the biggest mackerel you can conceive of, like a tiny little mackerel but the size of a grand piano. That’s kind of what we’re talking here. It’s a fish that evolved between 65 and 55 million years ago in the late Paleocene. It’s the most remarkable color.

Photographs do not do this fish justice. It’s almost like a rainbow in all the colors as they shift on its body. And it has these extremely sharp-looking fins. Its tail almost looks like it can be a weapon. It kind of has these really sharp points. It’s a remarkable creature.

IRA FLATOW: And it can live up to how long?

KAREN PINCHIN: So like a lot of things about the ocean, it’s hard to get exact numbers here. But generally between 18 and 30 years is our understanding, which is magnitudes more than any other tuna species.

IRA FLATOW: And you say that it can change its skin color. It reminds me of an octopus.

KAREN PINCHIN: It’s a phenomenon called flashing. And it most often occurs when a fish is fighting or stressed or while it’s dying. And its skin can go from black to white to silver to mauve to teal. It’s really, really spontaneous. And only very lucky fishermen get to see it. It’s quite remarkable.

IRA FLATOW: Wow. Wow. That is remarkable. Now tell me how a bluefin is different from an albacore or a yellowfin tuna.

KAREN PINCHIN: So the primary difference is how it evolved to swim in the open ocean. So they’re technically part of the same family. That family is scombridae. But very early on, back when the continents were still connected and you had the Tethys Sea, it was a precursor to the Mediterranean, that was where the bluefin tuna evolved.

And then as the continents separated and the bluefin had to go farther afield into the Atlantic Ocean to find food, it developed this incredible system called a rete mirabile system. It’s like a heat pump in its body essentially. And it allows it to be warm-bodied. So it takes all the heat that a lot of other fish would lose through their gills and actually recycles that heat back into its muscles, its brain, its eyes allowing it to really make these remarkable speeds.

An example of that is, in 1962, one fish that was tagged by a scientist near the Bahamas migrated 10,000 kilometers in 50 days and was caught off the coast of Norway. So that’s like five consecutive marathons a day for more than a month.

IRA FLATOW: Wow. That is amazing. And tuna have a sort of third eye, right?

KAREN PINCHIN: Yes. This is one of my favorite tuna facts is that it has a little translucent window called a pineal window on the top of its head. And that’s connected to an organ in its brain like a piece of cartilage that essentially senses light. And so it does these incredible super deep dives called spike dives very often when it’s breeding and spawning. And that little window allows it to sense light and day and depth.

IRA FLATOW: That is cool. How did you get hooked on tuna? What drew you into researching and writing a book about this fish? I mean, I’ve loved tuna my whole life– eating it that is. But you’re researching it. What drew you in?

KAREN PINCHIN: So I’m part of a generation that has been taught our whole lives– save the bluefin. That has been the mantra is that, by eating this fish, you’re somehow morally complicit in its oncoming extinction. But I grew up far in land in Ontario in Canada. And I would fish lake fish– a floppy bass, a trout– but didn’t really a lot about saltwater fishing. This was a new world for me.

But I had been writing about restaurants and culinary culture and science for quite a long time when I got a phone call from a scientist named Molly Luckovich when I was doing grad school in New York. And she said you will not believe the story of this fish. And the fish came to be called Amelia for Amelia Earhart, a woman who I said crossed the Atlantic Ocean on currents of a different kind.

And it was tagged first by a man named Al Anderson, a charter captain in Rhode Island. Three years later, she tagged the same fish, which just that in and of itself is extremely unlikely– tagging a fish this size again. And then the tuna wore a pop-up satellite tag. She tracked it as it moved up the Eastern seaboard. And then it disappeared until 2018 when this one fish crossed the Atlantic Ocean, spawned, left the Mediterranean, and was caught in a Portuguese set net and was killed and shipped to the world’s second largest fish market in Madrid.

And so the ability to track that fish over that period of time, the fact that transatlantic migration is something that science hasn’t incorporated into models for decades and decades– this was a remarkable fish. And it had been tagged by some remarkable humans. And so that was the story. And the more I got into it, the more I realized that there were all these themes of history and culture and science and crime that were encapsulated in these arguably simple-seeming stories.

IRA FLATOW: I want to know more about Amelia’s journey because, from reading your book, I understand it was vital to really upsetting our ideas about tuna’s migratory patterns, things that we didn’t know before.

KAREN PINCHIN: And that’s one of the most outrageous things about fishery science is that so much of what we take for granted now about how fish move, how we manage the stocks. Even just the word stock implies like a certain degree of commercial value. But a lot of the science is so young compared to other fields. And so this one fish, it broke a line. And this line was drawn in 1981 at ICCAT, which is the international body that manages tuna.

And it was a move championed by the United States whose delegation said, listen, if the Europeans won’t reduce the number of tuna they’re catching, we’re going to draw a line down the middle of the ocean. All the fish on the western side, those are ours. All the fish on the eastern side, those are yours. They set quotas for the Canadian government, the US government, and the Japanese fleet that had been historically catching tuna in, quote unquote, “our” waters.

And that was it. That was how the fish was managed as two stocks that spawned in two different places– one in the Gulf of Mexico and the other in the Mediterranean. And any fish that kind of went back and forth, they were considered anomalous. And over decades of dedicated tagging and tracking these fish from the air and watching catch landings and analyzing the otoliths, the tiny little ear bones, scientists are starting to understand that maybe this framework that set all these quotas and determined international management, maybe they’re just not useful anymore.

IRA FLATOW: They’re not accurate. In the book, you chart the story of Al Anderson, a fisherman based in Narragansett, Rhode Island. His business model was taking out people on his boat where he tagged bluefin tuna and then putting the tuna back in the ocean. I mean, what can his story help us understand better about the bluefin tuna?

KAREN PINCHIN: I think first off is the power of the individual action in the face of something that seems incomprehensible– tagging one fish and putting it back into the ocean– this huge, huge body of water. What are the chances it’ll come back?

IRA FLATOW: And he was doing this by himself.

KAREN PINCHIN: Yeah. Yeah. Just one man on a boat. Sometimes, he had a first mate. He collaborated with a Woods Hole scientist named Frank Mather III who pioneered giant bluefin tagging in the US. He loved the respectability, I think, that the tagging gave him. He loved the data that he would get back out of it. And I get into his personal story. He had a very hard childhood and teen years and parental situation.

And he used the tuna as a way to kind of– and striped bass, which he tagged as well. Over his lifetime, he tagged more than 60,000 fish. And about 5,000 of those were juvenile bluefin tuna. And I think, ultimately, it’s this idea that, do you have to be a perfect person in order to do interesting or good or useful science, even if it’s citizen science? And I think that’s the thing that helped me develop a real affection for Al who passed away before I even had the chance to discover his story.

IRA FLATOW: Walk me through a bit about bluefin tuna history and popularity because I remember there was a time where the tuna were being overfished. I think it was in the 1990s. How did their numbers eventually rebound?

KAREN PINCHIN: This is such an interesting story where, in some cases, the scientists they loathed some of the environmentalists. These people were really, really battling it out. But there were a lot of factors. One of the factors was that we needed better data. We needed systems that said, where are these fish? How many of them are we catching?

Part of it was that we did have to bring in a moratorium in the United States and Canada. Al said this in his books that he wrote. A lot of US fishermen don’t understand that we are fishing under a scientific quota. All the bluefin tuna that were caught basically throughout the ’90s in the yachts, a lot of those fish were technically for science.

But when a single fish is being sold for $50,000– $50,000– then the market has this kind of real power. So one of the issues is also that there was a large criminal market. When something has that kind of value, when you have that kind of demand, there’s a real scramble. And then the last thing is that the quotas that were being set internationally, the body that I mentioned, ICCAT, it was rife with political influence.

The science was just– the scientists would say maybe this year we should catch only 10,000 metric tons. And all the delegates from all these tuna fishing nations would say, well, like thanks for the advice, but we’re going to set the quota at 30,000 metric tons. That’s a lot of tons. That’s a lot of tuna.

IRA FLATOW: If you’re just joining us, we’re talking with Karen Pinchin, author of a new book, King of Their Own Ocean: Tuna, Obsession, and the Future of our Seas. This is Science Friday from WNYC Studios. As you’re describing this, I’m thinking to myself, and I’m sure my listeners are too, and I think about it every time I open a can of tuna fish, is there a way to ethically eat tuna?

KAREN PINCHIN: There is. And that has been a very modern emergence that has come from this better science and from this better management. And I had sushi last week. I had bluefin tuna at my local sushi restaurant. And because it’s locally caught on either rod and reel, that’s where you have one fishing rod, one fish, or by harpoon, that’s one harpoon, one fish, and it’s one of the tightest managed, most productive fisheries on the planet right now.

I talked to scientists who’ve spent the past 30 years trying to save the bluefin. And they said it’s now not a fish I worry about. Carl Safina, a couple of years ago, went out with a friend on his boat off Montauk and caught a bluefin tuna. And they kept it. He was the environmentalist who essentially led the charge against a global trade in bluefin tuna in the ’90s.

And now it’s healthy enough that even people who would have condemned it years ago are now saying that now we have other things to worry about like forage fish, herring in the North Atlantic. Hopefully, this is a hopeful story that can be used as a template, as a framework in the face of a really dire situation, how individual action can actually make a difference.

IRA FLATOW: It almost sounds like we’re in the middle of climate change and global warming that it may be helping the tuna out some way.

KAREN PINCHIN: That’s a very strange silver lining in this whole story is that bluefin tuna need waters of 22 degrees Celsius or warmer to breed. And it means that all these places where it would otherwise reproduce– Gulf of Mexico, Mediterranean– those are warm places. And it can range so widely in the ocean that a lot of scientists say, in some cases, populations may be recovering because of climate change because it can benefit from the warming waters. But that is in the short and medium term. The real danger is that we’re just playing God with all these unintended consequences. So I would say that it will benefit with a grain of salt.

IRA FLATOW: Karen, a fascinating book. Thank you for writing it, and thank you for being a guest.

KAREN PINCHIN: Thanks so much, Ira.

IRA FLATOW: Karen Pinchin, science journalist, author of the new book, Kings of their Own Ocean: Tuna, Obsession, and the Future of our Seas. Karen is based in Halifax, Nova Scotia. And if you want to learn more about tuna and read an excerpt of the book, it’s on our website, sciencefriday.com/tuna.

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