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Bruce Collette on the sad state of tuna stocks

Zoologist Bruce Collette told EarthSky why bluefin tuna is among the most important – and distressed – of fishes.

Last week, fisheries managers from all over the world discussed the state of the world’s tuna stocks at a meeting known as KOBE III (July 12-14, 2011), which was held in La Jolla, California.

EarthSky spoke to tuna expert Bruce Collette, a senior zoologist at the Systematics Laboratory of NOAA’s Fishery Service located in the Smithsonian National Museum of Natural History, to find out what makes tuna so important – and so distressed – among fishes. Collette published a short paper about some of the challenges tunas face in the July 14, 2011 issue of Science, a globally respected science journal. He told us:

They’re are among the top predators. And … we fish down the food chain. We start with the biggest, most valuable species, and when that gets reduced in population, we go down to the next one, and the next one, and the next one. So if you remove the top predator, you’ve disturbed the entire food chain.

Image Credit: Sifu Remka

Dr. Collette said he’s especially concerned about the overfishing of three species of bluefin tunas – Atlantic, Pacific and Southern. The International Commission for the Conservation of Atlantic Tunas (ICCAT) stated in 2009 that the Atlantic bluefin tuna population dropped dramatically over the last 40 years – by 72% in the eastern Atlantic, and by 82% in the western Atlantic. Dr. Collette said part of what’s propelling the overfishing of bluefin tuna, today, is their high value. In Japan and Hong Kong, Dr. Collette told us, a single fish can fetch tens of thousands of dollars, for use in sushi and sashimi. Recently, he said, one 720-lb Pacific Bluefin was sold in the Tokyo market for $396,000.

The cost of these just keeps going up and up, there’s a high motivation for people to go out and catch them.

It’s hard for tuna to bounce back from the overfishing, he said, because of the particulars of their biology.

These … have a longer life than other fishes and this means that it takes longer for them to repopulate themselves. That is the additional problem.

Image Credit: David Remsen

Bluefin tuna can live 15 to 30 years. Other, smaller species of tuna live less than five years, so it’s easier for them to bounce back.

And one further problem of the bluefin tunas is that they have a mechanism that allows them to be warm-blooded, and they can extend their feeding range into cold water, and grow very rapidly. But because of their evolutionary history, they have to return to warm waters to spawn, like all other tunas…. The Southern Bluefin, which is widespread in cold temperate waters, has to return to a small area between Australia and Indonesia to spawn, and this is an area in which fisheries were concentrated, which reduced the stock seriously.

He said that there are strategies that work to help improve tuna stocks – fishing quotas for tuna catches, for example. There are already established quotas for tuna catches around the world, he said. The problem, he added, is that laws preventing overfishing are either not enforced, or ignored.

The upper end has to be protected by the Regional Fishery Management Organizations (RMFOs) and the governments behind them, and they have to listen to the scientists when they’re given estimates of [fishing] quotas. And, historically, the scientists say you can catch this many, and somebody fuddles in there and says, “Ah, no, we can double that.”

He mentioned an instance of illegal tuna fishing going on in the Mediterannean – 50,000 metric tons of tuna were fished, when a quota of 30,000 was offered. And that quota was already too high, he added. That’s a symptom of something happening all over the globe. According to the Pew Environment Group, which is heavily involved in the Kobe III meeting on the state of the world’s tuna stocks:

Collectively, the convention areas of the tuna RFMOs (Regional Fisheries Management Organizations) cover over 325 million km2, or 91 percent of the world’s ocean surface. Within these areas, over 4 million metric tonnes of tuna are caught annually by tens of thousands of vessels, many of which move from ocean to ocean over the course of a year. The need for coordinated management of these fisheries is clear.

We asked Dr. Collette what all this means – especially when you head out to a sushi restaurant. He explained that it’s good to limit your intake of tuna, but that most tuna served in sushi restaurantts in the United States is yellowfin tuna.

You’re probably getting yellowfin, and yellowfin is not in great shape but it spawns worldwide in tropical waters, so it can rebuild faster. So I don’t really worry so much about ahi, which is yellowfin. Further, the International Sustainable Seafood Foundation is working the other end, the canned tuna end. And they’ve gotten a lot of the major worldwide tuna canners to agree to only buy tuna from sustainable populations, and they just recently added a couple more canneries. So that is going to protect the smaller species. But the bigger species, there’s a lack of sufficient control. There are quotas, but, historically, these have not been well-enforced.

Bottom line: Bruce Collette, a zoologist with NOAA’s Fisheries Service at the Smithsonian Institution, said bluefin tuna is among the most important – and most distressed – of fishes. He said their stocks are in trouble because we’re not enforcing fishing laws designed to protect them, and because of the particulars of their biology: they reproduce slowly.

Beth Lebwohl

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