Tuna are the gold of the ocean—and, because certain species are so sought-after, they’ve become synonymous with overfishing and modern slavery. But in some areas, populations that were teetering on the edge of total wipe-out seem to be making a tentative comeback. Are things finally turning around for these fisheries?
They had started paying out the line the previous afternoon, steaming ahead at full speed while sending mile after mile of three-millimetre-wide monofilament out behind them into the Tasman. Every 11 seconds or so, the crew clipped a snood—a 14-metre-long length of nylon—onto the main line. On the end of the snood dangled an arrow squid the size of a man’s hand, and a 60-gram lead weight.
By the time they were done, it was dark, and the main line stretched for about 30 nautical miles, invisible beneath the surface of the water. In the far distance, the Southern Alps glowed white above the West Coast.
For Michael Smith, the boat’s captain, it was his first surface longlining trip. Universally known as Smithy, he grew up in Greymouth when there were only a couple of choices for a bloke looking for physical work: you could go down the mines, or you could go to sea. Smithy was 15 when he chose the sea.
Since then, he’d tried his hand at inshore trawling, deepwater trawling for orange roughy and hoki, and bottom longlining for ling, hāpuku and bluenose. At 44, he wanted a new challenge. Trawling was mechanised, but longlining for tuna was hands-on—a personal fight with each individual fish.
When the crew started hauling the line in again, in the middle of the night, hook after hook had a fat tuna attached. Smithy grinned—they’d struck a school of big, oily, yummy fish.
As the boat approached each fish, one of the crew unclipped the snood from the main line and transferred it to a fight line. The men’s attention turned to that one animal. Smithy took the fight line in gloved hands, feeling the pull of the fish below, battling for its life.
The line slackened and he knew the fish was winding up its strength. “Ooh, he’s going to run!” called Smithy. Then, twaaang, the line shot away from him, his hands burning as it slid through his grip. He let it slide. He needed to play the fish, let it run for a bit, then let it know who was boss. You couldn’t just wang the fish in a hauler and bring it up using the brute force of a hydraulic lift—that would only rip the hook out of its mouth.
Smithy fought the hefty bluefin to the side of the boat, then the three other crew helped to hoist its glistening gunmetal body onto the deck. It weighed perhaps 150 kilograms. One of the men shoved a stainless-steel spike into a little dimple on its head, killing it instantly, then slipped the deck hose into its hot insides for 15 minutes to flush the blood out. Smithy went back to the wheel, gunned the engine, and moved the boat on to the next hook.
Soon, there were eight or ten massive fish on the deck, blood trailing behind the boat, sharks circling in the water. Smithy was surrounded by life—and death. “Wow,” he thought. “This is a frickin’ blast.”
It was 8am by the time they’d hauled in the last fish. Smithy had just worked 18 hours straight—but that was the nature of fishing. You worked until the job was done. Hard work, but it came with such an adrenaline rush. “I dunno if I’ll ever grow out of this,” he thought.
Tuna are some of the largest, fastest, most finely tuned fish in the sea: schooling, torpedo-shaped, migratory hunters. Humans have hunted them in turn for thousands of years. We stamped their image onto coins in ancient times, and incorporated them in music and art from the Mediterranean Sea to the Pacific Ocean. Today, tuna are one of the world’s most lucrative fish, netting US$40.8 billion globally in 2018, according to a report by United States-based policy research group the Pew Charitable Trusts. Tuna fisheries employ people in more than 70 countries, and sustain the economies of multiple Pacific Island nations. But soaring demand for tuna over the past 50 years has decimated global populations. Forced labour and abusive working conditions are rife in some offshore fleets, and controversies abound over bycatch and damaging fishing methods.
The same six species of tuna fished commercially in New Zealand waters—southern bluefin, Pacific bluefin, yellowfin, bigeye, albacore and skipjack—are also caught by small-scale fishers in the coastal waters of Pacific nations, and by industrial purse-seine vessels and longliners operating in the island states’ exclusive economic zones and in the remote high seas.
The Western and Central Pacific Fisheries Commission (WCPFC), established in 2004 to conserve stocks of tuna and other highly migratory fish, is the organisation that manages the populations of tuna fished in the area: albacore, skipjack, yellowfin and bigeye. In 2019, the region’s catch of all four species totalled three million tonnes—the largest in history. More tuna are caught in the waters off Kiribati each year than in the entire Atlantic Ocean. Even so, according to the latest stock assessments, all four tropical tuna populations are in the green. And according to Francisco Blaha, a fisheries consultant for Pacific Island nations who’s based on Auckland’s Waiheke Island, when it comes to the sustainability of tuna catches, the western and central portion of the Pacific is actually doing better than anywhere else in the world.
The situation is different for two species fished in the New Zealand region: the most valuable tuna, southern bluefin and Pacific bluefin, which migrate south in winter to the waters all around New Zealand. They’re targeted by a few dozen surface longliners off the South Island’s West Coast, like the one Smithy works on. Smithy’s crew mostly catch southern bluefin, but they’ll occasionally haul up a giant, even more lucrative Pacific bluefin.
“We refer to them as a lottery fish—it only takes one hook to turn your whole trip around,” says Smithy. “I’ve never had one of those really monster bluefins, but I might get one next week. That’s the beauty of it.”
The southern bluefin Smithy catches are mostly destined to become sashimi in Japan. Each fish will be laid out on the floor at fish markets and auctioned to the highest bidder. In 2019, a 278-kilogram Pacific bluefin caught off Japan was bought at Toyosu Market in Tokyo for a record NZ$4.3 million by the attention-seeking owner of a Japanese sushi restaurant chain. On a normal day, Pacific and southern bluefin net around $38 and $35 per kilo respectively, according to Pew, meaning each fish is still worth thousands of dollars.
On Smithy’s boat, the fish are treated accordingly. The deck is covered with carpet to minimise damage to their shiny skin. On some longliners, tuna are carefully wrapped in muslin shrouds and placed in ice in the hold. Smithy’s current vessel has a refrigerated brine tank instead, filled with water chilled to below zero. After being bled, gutted and gilled, the fish are given unique tags to identify them, and immersed in the tank as soon as possible after leaving the sea, to prevent deterioration. “Every fish is precious,” says Smithy. “We treat them like a baby, apart from the fact we’ve killed them.”
The Japanese like their tuna perfectly unblemished, he says—unless there’s a good story behind the damage. Sometimes a mako shark will attack a tuna while it’s on the line, biting the tail off so the fish can’t swim away. “We actually get quite good money for them sometimes, if it’s a bit garked up and it’s died in battle with a shark. It’s got a bit of mana, I suppose.”
The animal itself is worthy of respect, says Smithy, but it’s his job to catch it, and he loves the work. “In a perfect world, maybe we shouldn’t be hunting the apex predators… but it’s a good living, and it’s a good clean fishery. I certainly don’t want to drive any species to extinction. That’s not logical. You want them to survive.”
It’s hard to judge a fishery over just seven years, Smithy acknowledges, but it looks healthy enough to him. “From what I see, there’s no shortage of tuna around where we work. But I don’t know what goes on overseas.”
That is the challenge when it comes to globe-trotting fish like tuna. They may visit New Zealand in some seasons, during some stages in their life cycle, but their peregrinations depend on climate and currents, and take them across oceans and borders. Managing tuna fisheries requires cooperation, diplomacy and negotiation between countries that don’t always see eye to eye. For the past 30 years or so, those negotiations have taken place within regional fisheries management organisations like the WCPFC.
The story of the southern bluefin tuna is both a cautionary tale and a cautiously hopeful example of success.
Southern bluefin are powerful hunters, eating fish, squid and crustaceans. Their warm blood supercharges their muscles, allowing them to accelerate at twice the rate of a Ferrari, and keep up a steady pace of three kilometres an hour for weeks at a time. They live for much longer than other tuna species, up to 40 years, and the largest of them top two and a half metres in length and 260 kilograms in weight. Unlike skipjack tuna, which are sexually mature at the age of one or two, southern bluefin don’t reproduce until they are at least eight years old.
“It’s kind of the difference between rhinos and rabbits,” says Amanda Nickson, the director of international fisheries research and advocacy at Pew.
Then again, a rhino has one calf every two to five years. When a female southern bluefin spawns, she releases several million eggs into the warm seas south of Java, where the entire population of adult southern bluefins meets each summer to breed. It’s not known whether all female southern bluefins spawn every year, and only a fraction of those eggs will survive the terrors of the open ocean, but those that do follow the Leeuwin Current down the west coast of Australia.
In the summer, the juvenile fish hang out in the Great Australian Bight, where some of them are rounded up by South Australian vessels and towed to aquaculture pens in Port Lincoln to fatten up. Adult tuna leave their tropical spawning grounds in the autumn and migrate to the cool, deep waters of the southern Atlantic, Indian and Pacific oceans to feed.
Commercial vessels started fishing southern bluefin in the 1950s, and the global fishery peaked in the early 1960s with more than 80,000 metric tonnes taken in one year. (In New Zealand, most of the southern bluefin catch was used for crayfish bait.) Fisheries management aimed to maximise catches, not sustainability. In the late 1970s, the southeast Australian southern bluefin fishery collapsed, and by the early 1980s it was clear that the species as a whole was in trouble.
In 1989, Australia, Japan and New Zealand began discussing what to do. They set a global quota of 11,750 tonnes—about half of what the catch had been in previous years. (In 1989, New Zealand also voluntarily set its quota far below that of other countries, at 420 tonnes compared with Australia’s 5265 tonnes—apparently as a “grand green gesture”, says tuna governance expert Kate Barclay from the University of Technology Sydney.) The convention they agreed on came into force in 1994, with the Commission for the Conservation of Southern Bluefin Tuna (CCSBT) formed to administer it.
Over the next few years, there were heated disagreements over how many southern bluefin were left—the estimates were full of uncertainty and relied on logbook data from Japanese longline vessels—as well as what the total catch should be, how it should be divvied up between the nations as quota, and whether Japan should be given additional quota to allow for research. Australia and New Zealand argued there were too few fish to allow some to be caught for scientific purposes, and no country wanted to give up any commercial quota for research. In 1998, Japan declared it would take a 1425-tonne scientific quota anyway, so Australia and New Zealand took Japan to the International Tribunal for the Law of the Sea over it. Tensions were high, and because the countries couldn’t agree, the quota remained what it had been since 1989.
Seeking to reduce the conflict, in 2002 the CCSBT began working on a “management procedure” for southern bluefin tuna, meaning that the total catch would be determined in response to scientific research, rather than as a result of negotiation. But in 2006, a scandal erupted that undermined confidence in both science and international cooperation: an independent review of southern bluefin sold in major Japanese tuna markets revealed there had been substantial, continuous under-reporting of longline catches dating back 20 years. Australian researchers say a significant proportion of the illegal catch was taken by Japanese fleets. Since much of the available information about the abundance of the stock relied on data collected by these fleets, the population estimates were probably also inaccurate. The unreported catch equated to 178,000 tonnes—more than double Japan’s agreed quota over the period.
The report was never made public, and Japan did not accept the findings, but agreed to halve its quota for the next five years. A 2009 stock assessment revealed that two decades of international management had not been able to increase the numbers of fish. The global catch was 10,941 tonnes—the lowest in more than 50 years—and the numbers of breeding adults were estimated to be just five per cent of what they’d been before commercial fishing began. Southern bluefin numbers had declined so quickly that, in 2011, the International Union for Conservation of Nature (IUCN) listed the species as “critically endangered” on its Red List. Some scientists said the species was unlikely to recover. The same year, the CCSBT finally agreed on a management procedure, a set of science-based rules that would be used to determine catch limits. Its goal: to build up southern bluefin tuna numbers to 20 per cent of the original, unfished spawning population by 2035, while allowing for commercial fishing.
This system has really turned things around for the southern bluefin, says Nickson. “It’s close to a world first, and it’s the reason that you are starting to see some incremental improvements in that population. It means that science is at the very heart of the decision-making every time. And the industry considers it one of the best things that was ever done.”
It was so successful, in fact, that the CCSBT’s modelling estimates that the tuna population has increased by around five per cent every year since 2011. It reached the 20 per cent goal early, in 2020. In 2018, the total catch was increased to 17,647 tonnes per year, where it has remained. A new management procedure has been adopted, with the goal of reaching 30 per cent of the original tuna population by 2035. (Non-profits such as WWF and Pew argue that 40 per cent is a safer target, providing a buffer against climate change or other shocks.)
“Southern bluefin tuna is really a good-news story,” says Ann Preece, a fisheries scientist at Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO).
New Zealand’s southern bluefin quota is currently set by the CCSBT’s management procedure at 1088 tonnes, of which 1046 tonnes are allocated to commercial fishers, with 20 tonnes to account for discard deaths and other mortality, another 20 tonnes to reflect the sudden growth of the recreational fishery, and two tonnes to reflect Māori customary fishing. In 2019, then-Minister of Fisheries Stuart Nash set a recreational bag limit of one bluefin per person per day “until we understand more about this highly variable developing fishery”.
When the bait hits the water, it’s quiet for a moment, and then the feeding frenzy begins. Kris Miletic pulls on his wetsuit as the crew encircles the school of southern bluefins in a purse-seine net the size of a football field. Another boat manoeuvres an even larger floating cage into position nearby.
Then it’s Miletic’s turn. He jumps into the purse-seine net, wearing just a mask and snorkel. At first, all he can see is water, then he’s surrounded by fish. One swims lightning-fast towards him and turns at the last millisecond, centimetres from his face. The rest of the world disappears, and it’s just Miletic and the tuna. Like them, he’s part of the food chain.
Miletic’s job right now is to estimate the number of bluefin in the net, and how old they are. Last time they set the net, he guessed 4500, and he was pretty close—there were 4800. If too many are too small—juveniles aged two or three years old—the crew might decide to open the net and let them swim free. But these fish are mostly around eight to ten years old, so Miletic connects the net to a sea gate that opens into the floating cage.
The purse-seine captain starts drawing up the net, and the tuna are channelled into the pen. Underwater, Miletic counts every tenth fish with a hand-held “fish clicker”, and a video camera records numbers as well. It takes just six minutes to transfer 400 fish.
He climbs aboard. Already, spotter planes are searching the Great Australian Bight for other schools of tuna, and while the weather holds and the fish are abundant, Miletic and the crew repeat the process until the tow pen contains somewhere between 13,000 and 15,000 southern bluefins.
Then they start the long, slow trip home to Australia’s tuna capital, Port Lincoln, dragging the cage behind them. Travelling at just one knot, the journey can take several weeks. Once a day, sometimes more, Miletic suits up and gets into the pen, checking for signs of illness in the tuna or damage to the cage, such as a shark ripping a hole in it. By the time they arrive at Port Lincoln, the fish are so used to Miletic’s presence he can just about touch them.
The fish are transferred into large, circular farms floating in Boston Bay. They spend the next four to six months getting fed sardines twice a day, eating as much as possible. “It’s just an ongoing smorgasbord from sun up to sun down for these fish,” says Miletic.
Finally, in late winter, it’s all over. The fish have fattened up, reaching anywhere from 18 to 50 kilograms. A small purse-seine net is shot off inside the pen, capturing around 700 tuna—the number that can be processed in a day.
Miletic, wearing neoprene dive gloves, positions himself in the net near a conveyor belt that runs from the water’s surface up into the fishing boat. Then he grabs each fish with his hands as it swims past him. “It’s all timing and precision.” He grasps the tail first, then flips the heavy fish upside down and back to front—a disorienting position that momentarily stuns it. Then he puts his hand on its nose and guides it into the conveyor belt. “I can do that move every 10 seconds—bloop, bloop, bloop—but it’s taken me a lot of years to get in tune with these fish and practise my techniques to be able to harvest them like that.”
On the boat, the fish is spiked, bled, gutted and placed in a tank full of ice, until it is transferred to a Japanese freezer ship, flown directly to Japan’s fresh-fish markets or, increasingly, sold to Australian restaurants and retailers.
“I don’t look at them as a piece of sashimi. I look at them as a species,” says Miletic. “I find them quite intelligent. I feel so comfortable with them. They are a beautiful animal.”
If he feels any discomfort over what he does, he says, it’s no different from that of a farmer who loves his cows but turns them into beef.
Three decades ago, no one thought that voracious, migratory tuna could thrive in a cage, but ranching has been so successful that the vast majority of Australia’s 6165-tonne quota of southern bluefin is now harvested from the pens off Port Lincoln.
The remote town of around 16,000 people lies near the tip of South Australia’s Eyre Peninsula, more than seven hours’ drive from the state capital, Adelaide. For two generations, tuna has been such big business that the place reputedly has more millionaires per capita than any other Australian locality.
In the 1950s, immigrant Europeans began pole-and-line fishing for southern bluefin in the area. They switched to purse-seining in the 1970s, around the time that Miletic’s boat-builder father arrived in South Australia from Croatia and got work building steel tuna boats. The town endured tough times when the global catch limit was slashed by 70 per cent in the early 1990s, though. A new strategy was called for, and some local fishers pioneered the idea of tuna ranching. Now, the practice has spread globally. According to industry spokesman Brian Jeffriess, the chief executive of the Australian Southern Bluefin Tuna Industry Association, 70 per cent of the global market for premium sashimi is now produced by farming, while the remaining 30 per cent is caught by longlining operations like the one Smithy works on.
The contrast between Smithy’s and Miletic’s jobs—the fact that fishing for southern bluefin looks so different in Australia from how it is in New Zealand—has led to international tensions.
Australia criticises New Zealand over its high levels of seabird bycatch, says Jeffriess, who attends the CCSBT’s annual meetings. “Bycatch is the skeleton in the cupboard in this fishery, and New Zealand’s performance on seabird bycatch is a very sore point with the other countries.”
New Zealand reported to the CCSBT that 167 albatrosses and 79 giant petrels were killed as a result of fishing for southern bluefin tuna in its waters in 2019.
That means for every 10,000 hooks that hit the water in New Zealand, four albatrosses were killed—a much higher rate than for Australia’s tuna longline fleet.
Stephanie Borrelle from BirdLife International says the real number of deaths is likely higher. Bycatch numbers are either self-reported by fishers or recorded by independent fisheries observers, who are required by the CCSBT to be present on only 10 per cent of bluefin tuna fishing trips. (Pacific-wide, COVID-19 disruptions have meant that observer coverage on tuna boats has dropped dramatically.) Fisheries New Zealand’s own reports indicate that non-fish bycatch is significantly more likely to be reported when an observer is on board.
By contrast, Australian tuna longliners are required to have cameras, and authorities randomly review about 10 per cent of the footage. Unreported seabird bycatch leads to the vessel being flagged and investigated, meaning compliance is high, says Borrelle.
In New Zealand, cameras are deployed on around 20 boats fishing along the west coast of the North Island, where the fishers are likely to encounter Māui dolphins. The rest of the commercial fleet—including surface longliners fishing for tuna—isn’t yet required to have cameras. Though the addition of cameras to all fishing vessels is planned, it has been repeatedly delayed. Fisheries New Zealand now says there will be cameras on 345 inshore vessels by 2024, and surface longliners fishing in high-risk areas, where there are a lot of albatrosses and black petrels, will be prioritised.
Birds and fishing boats are drawn to the same rich waters, and longline bait is irresistible to an albatross. “There are mitigation measures that work, but you have to use all of them, and you have to follow them diligently,” says Borrelle.
Currently, surface longliners fishing for bluefin tuna have to use a tori line: a string running above the main longline with metre-long fluorescent streamers to deter birds. In addition, fishers must either set their line at night, when seabirds are less active, or add extra weights so the line sinks quickly out of the birds’ reach.
These days, Smithy almost always sets his line at night. If a hook comes up with bait still on it, the crew don’t throw it over the side like they used to, but store it on board so birds aren’t encouraged to follow the boat. Smithy has even made his own seabird deterrent: lengths of bamboo strung over the part of the boat where the fish are hauled aboard. Observers come on his boat every year to check the processes.
Despite all these measures, there are times—especially around the full moon, says Smithy—when catching a few birds is unavoidable. If a big fish on the hook fights its way to the surface, it might bring other baited hooks up with it.
“On some trips, you might get half a dozen [birds] in one set,” he says. “We don’t want to be bloody catching them. I quite like the old seabirds, the big dopey buggers, hooning around.”
In 2020, a New Zealand vessel fishing for Pacific bluefin tuna off East Cape caught four endangered Antipodean albatrosses on one line, even though it was following regulations—setting during the day, but using a tori line and weights. That suggests the current measures are insufficient, says Borrelle. “And it’s a huge loss. Antipodean albatrosses have declined by 42 per cent in the last 15 years.”
At the CCSBT’s 2020 meeting, BirdLife International singled out New Zealand (alongside Japan) for its “unacceptably high” numbers of seabird deaths, and urged the country to adopt more stringent measures. New Zealand said the majority of fishers were following the rules, but there isn’t actually any proof, given the lack of cameras and the low number of observed trips. “It’s easy to lay blame elsewhere, but we can’t say for certain that those seabirds are not being caught on New Zealand boats,” says Borrelle. “Until we have electronic monitoring of some kind—maybe not cameras, but some way of verifying that they’re using these mitigation measures correctly, then we can’t tell other countries to do the same thing.”
Meanwhile, New Zealand is taking issue with the way Australia counts fish and estimates the weight of juvenile bluefin entering the Port Lincoln pens. The weight determines whether Australia is sticking to its quota—but because the fish aren’t killed until later, the ranchers can’t weigh them directly. Instead, they rely on video footage of the fish entering the farms from the towing pens and use algorithms to convert the estimated lengths of the fish into tonnes. It’s not a perfect science, and negotiators from New Zealand and some other countries think the Australians should try a different technique that’s used in Europe—stereo video—which they say is more accurate. Australia disagrees and is “dragging its feet” in improving its estimates, says Glen Holmes, a marine ecologist with Pew’s international fisheries programme.
New Zealand government negotiators feel so strongly about the weight-estimation issue, though, that in 2019 our representatives said they wouldn’t accept any changes to the total catch unless Australia could show it had improved its counting techniques.
But non-profits, including Pew, say that decoupling catch limits from their science-based rules sets a dangerous precedent that could reintroduce “a climate of dysfunction” and undermine the system credited with bringing southern bluefin back from the brink.
The population of southern bluefin tuna is bouncing back—that’s something the negotiators generally agree on. But governments and fishing industries have been wrong about such things before. How can they be sure now?
New genetic sampling methods are giving scientists the most accurate picture yet of just how many southern bluefin are swimming around out there—and they don’t rely on reporting by the commercial fishing industry.
Usually, fisheries managers use physical tags to estimate abundance. A plastic, metal or electronic tag is inserted into the fins of a few thousand fish, which are released back into the ocean. The number of tagged fish recaptured later gives an indication of the size of a population. But tags can fall out, fishers can fail to return the data—or misreporting can distort the numbers. “There’s always an under-reporting rate of those tags,” says Preece.
So instead, every year CSIRO researchers take tiny muscle tissue samples, the size of a grain of rice, from about 5000 two-year-old southern bluefin tuna off South Australia. The scientists do a DNA test on each sample, which becomes an invisible, lifelong tag for that fish. The tuna, meanwhile, are released and continue their normal migration. Some head to New Zealand waters, while others swim into the Indian Ocean. But the following summer, most of them meet up again in the waters of the Great Australian Bight, where Miletic and his colleagues scoop up some of the now-three-year-olds and drag them into Port Lincoln.
A few months later, CSIRO researchers collect random tissue samples from 10,000 to 15,000 of those fish as they’re processed on the factory line and do another DNA test. Based on how many matches they get—how many of the tagged fish are caught the following year—the scientists can estimate the total number of two-year-old fish in the population, giving an early warning of problems with breeding that could affect future stocks.
“We wouldn’t be able to do this project if we didn’t already know quite a lot about southern bluefin tuna,” says Preece.
The first estimate of juvenile abundance using this method, in 2016, was 2.27 million two-year-olds, based on finding 20 matching DNA fingerprints between 3000 tagged and 15,000 harvested fish. In 2018, that number dropped to 1.15 million—but Preece cautions that breeding success naturally varies from year to year. The 2019 figures, which are still being analysed, look promising.
But it is CSIRO’s second tool, called close-kin mark recapture, that has scientists and the industry most excited. The method has taken 15 years to fine-tune, and gives researchers the ability to estimate the population of breeding adults—a crucial measure for assessing the sustainability of fishing. Instead of counting how often the same fish is caught twice, close-kin mark recapture assesses the probability of finding fish that are related to each other. Each year, CSIRO scientists take tissue samples from three-year-old juvenile southern bluefin tuna harvested from the pens in Port Lincoln and compare them with samples from breeding adults wild-caught in Indonesia. Genetic tests reveal the numbers of parent–offspring pairs among the sampled fish. “We’re aiming to get in the order of 50 pairs out of 15,000 samples, so it’s a needle in a haystack,” says CSIRO’s Campbell Davies, the lead scientist behind the research.
Complex formulae generate the final estimate of the number of breeding adults, but the principle is simple, says Davies. Imagine a small village, he says. If you chose 20 random people from that village, it’s likely that some of them would be related, or that you’d find a mother and child. If you plucked 20 random people from the streets of Auckland, the chances would be much lower. Similarly, the number of parent–offspring pairs the scientists find tells them whether there’s a village or a city of fish out there.
Close-kin mark recapture was pioneered for southern bluefin tuna in 2012 and incorporated into the CCSBT’s stock assessment for the first time in 2013. It showed that the population was larger than previous stock assessments had predicted. “I’m sure that helped generate enthusiasm for the technique,” says Davies, drily.
New genetic techniques called SNPs (the same ones used for COVID-19 tests) have also allowed Davies’ team to identify half-sibling pairs—fish born to one common parent over different years. That provides a separate measure of abundance, allows the scientists to check their working, and also tells them the parent has survived to breed again. “If you do enough of those over enough years,” says Davies, “then you can estimate what the mortality rate of the adults is without ever having seen them.”
In 2020, the population of spawning southern bluefin tuna (not including the more numerous juveniles) was estimated to be between 1.4 million and 1.8 million individuals, using the close-kin mark recapture technique. “We’ve demonstrated you can do this for an international fishery where there’s a lot of value, and a lot of political controversy and interest,” says Davies.
The method has since been adopted for estimating populations of New Zealand and Australian great white sharks. CSIRO is working with other regional fisheries management organisations to trial close-kin mark recapture for other tuna populations, including Pacific bluefin, Atlantic bluefin, the South Pacific albacore stock, and yellowfin tuna in the Indian Ocean.
All of those will be more complex than southern bluefin, says Davies, as the other species breed in multiple locations and are more numerous, meaning sample sizes need to be much larger to have a chance of finding a statistically significant number of matches. But those problems should be solvable. “It’s potentially quite applicable to a very broad range of fisheries, not just tuna, but it comes down to political institutional will.”
For South Australian tuna industry spokesman Jeffriess, the innovation “is about as good as it gets. If you’re investing heavily in value-adding and buying quota, you really need to be as sure as you can be about the future of the stock. That’s the foundation of everything.”
There’s no doubt that the future of southern bluefin is looking a lot better than it did ten years ago, says WWF’s Bubba Cook, a ponytailed Texan now living in Wellington. But we shouldn’t forget how bad things were, he cautions.
“There is this tendency for fisheries managers and the industry to pop champagne corks and pat themselves on the back whenever they recover a collapsed fishery,” says Cook. “That’s great, but it should never have collapsed in the first place.
“The fact remains that southern bluefin tuna is still an endangered species.”
Is that still true? The IUCN Red List calls southern bluefin “critically endangered”—but that assessment was made in 2011, before the species’ recovery.
Bruce Collette led the team responsible for that verdict a decade ago, and he’s just completed another analysis of all 61 species of tuna, mackerel and billfish (which include marlin and swordfish). Collette is a veteran ichthyologist who spent most of his 60-year career at the Smithsonian National Museum of Natural History in Washington and he’s also the chair of the IUCN’s Tuna and Billfish Specialist Group.
The group has just recommended to the IUCN that southern bluefin tuna be moved from critically endangered—the worst-possible status—up to endangered, but the IUCN has not yet made this official. IUCN ratings are derived in part from how much a species’ population has declined over three generations. Long-lived, late-spawning southern bluefins have long generations of 12 to 20 years, meaning three generations would encompass between 36 and 60 years. Due to overfishing, the species declined between 78 and 90 per cent over those decades, says Collette. “It takes a long time to recover from that.”
It also means the species must make consistent gains over the next few decades to climb out of its endangered status, he says. “Then it will probably be ‘threatened’, or ‘near threatened’, or ‘vulnerable’. Everybody is doing the right thing for southern bluefin. But it’s gonna take a while.”
Collette says the Red List criteria were developed for land animals, and acknowledges that the benchmarks are not perfectly suited to commercially fished marine species. His team has faced criticism from conservationists “saying everything’s a disaster” and fishers “saying there’s more fish than we’ve ever seen before”.
In the 1960s, Collette carried out fisheries research on Atlantic bluefin tuna. “I know how abundant bluefin were,” he says.
“Now, some of the fishermen say, ‘Oh, there’s so many bluefin.’ But that’s because they don’t know how many bluefin there were. We killed them.”
A fish population numbering in the millions doesn’t sound close to extinction, especially when compared to species like the Māui dolphin or New Zealand fairy tern, which have just a few dozen individuals remaining. But humans reduced passenger pigeons from billions to zero in just 50 years. A recent University of Otago study showed that the great auk—a puffin relative that thrived in the millions across the Arctic in the 1500s—was driven to total extinction by human hunting by 1844. And though the Atlantic cod fishery off Canada and the northern United States has essentially been closed since it collapsed in the 1990s, cod populations have failed to recover.
Ecosystems are complex, and we don’t yet know where tipping points lie for species that are naturally numerous. There has also been little research into the role southern bluefin tuna play in the wider ocean ecosystem. The species might be back up to 20 per cent of the unfished population—but less than a century ago, there were five times as many swimming from the tropics to the Southern Ocean each year. What other rhythms were lost as their numbers dwindled?
Climate change adds more uncertainty. Modelling predicts the Pacific stocks of skipjack and yellowfin tuna will move eastwards as the globe warms—out of the jurisdictions of some Pacific nations. And all the southern bluefin in the world breed in one location south of Indonesia, gathering to release their sperm and eggs at once. If something goes wrong—the waters get too warm, or too many adults are taken from the population for there to be the necessary critical mass to trigger spawning—breeding could fail to happen at all.
Even if the science shows a tuna stock is healthy, that doesn’t mean you can say the same about the people working on the fishing boats.
The complexity of tuna supply chains, and the difficulty of tracing fish back to where they were caught, has made it hard to hold people accountable for poaching or human-rights abuses (see page 64).
This cuts close to home for WWF’s Bubba Cook. In 2015, his good friend Keith Davis went missing while working as an observer on a tuna transshipment vessel in the eastern Pacific, 800 kilometres from the coast of Peru. Davis, an American, was the fourth fisheries observer to disappear on the job under mysterious circumstances in recent years. He is presumed murdered.
When Cook heard what happened, he tried to prevent the ship selling its haul of tuna, to hold the companies involved accountable and “hurt them in the pocketbook”. He contacted everyone he could think of but was told it was impossible: the supply chain was “too diffuse and opaque”.
“That fish ended up being offloaded in Panama, and so the product of a murder ultimately made it into people’s homes and onto their dinner plates.”
In the years since, Cook has made it his mission to champion new technologies that promise to untangle those murky supply chains and make tuna traceable. Pilot studies show huge potential. Satellites can be harnessed to show where fishing is occurring in places it shouldn’t, and artificial intelligence is starting to be used to review images, video footage and radio communications for illegal activity. “That will change the entire landscape,” Cook says. “We’ll no longer be in a situation where the sea keeps her secrets.”Rapid genetic testing, too, will give authorities more power to crack down on rule-breakers. In 2016, two Chinese vessels—the Da Yang 15 and Da Yang 16—were boarded by officials on a New Zealand government high seas patrol operation in international waters between New Zealand and Fiji. Genetic samples taken from the catch and sequenced back in New Zealand a few weeks later revealed that more than 100 tonnes of valuable southern bluefin had been misreported as lower-value bigeye. The following year, the Chinese government deregistered the fishing company and fined it $850,000. “China had to concede that they were fishing southern bluefin illegally,” says Cook. “Technology provided the smoking gun.”
Such genetic checks are about to get even easier, he says, with the recent development of a hand-held device that can confirm the identity of a fish in two hours.
Likewise, there should be no technical barriers when it comes to tracing tuna from bait to plate. Due to public health and legal concerns over E. coli, it’s already possible to track a head of spinach as it travels from the grower to a supermarket shelf. WWF has trialled blockchain technologies that will make it possible to do the same for fish, Cook says, and prevent fishing companies from falsifying information about their catch—but it will take political will and economic imperatives to force the industry and nations to implement them.
In the meantime, Cook says, the choice over which tuna to eat (see sidebar on page 62) isn’t clear-cut. “Until we can get that transparency in the supply chain where we can start to squeeze out the guys who aren’t doing the right thing and reward the guys who are, it’s going to be a real challenge for consumers to make well-informed and well-intentioned choices.”
One radical option for arresting the global decline in tuna populations was raised by American writer Paul Greenberg in his 2010 book Four Fish, written when Atlantic bluefin tuna was in dire straits. (The eastern Atlantic stock has improved so much in the decade since that Collette recommended the IUCN classify the species as “least concern”.)
Why do we empathise with and protect one sort of large apex ocean predator, Greenberg wondered, but see no problem with killing millions of another sort? “Whales have become wildlife,” he wrote, “but tuna remain food.”
A series of international conservation campaigns in the 1970s and 80s changed the way many consumers thought about whales and dolphins—though, as Greenberg points out, that philosophical shift was made easier by the fact that demand for whale oil had already collapsed. “By the time the Greenpeace Zodiacs hit the waves, whales as objects of commerce had become more or less irrelevant,” he wrote.
This is emphatically untrue for tuna. The huge sums of money that tuna represent would make such a transformation economically and politically challenging. But is there a moral case for reframing tuna as a creature worthy of our protection, a being worth more than its flesh? Cook suspects it may be an impossible dream: “It’s hard to hug a fish.”
Whales, at least, show affection for their young and sing to each other. Tuna, on the other hand… “It’s like getting someone to show affection for a locust,” says Cook.
“It’s hard to get people to love a big slimy animal that sprays its gametes into the water column and would eat its own young given the opportunity. I don’t think you could get people to show the same kind of compassion.”
New Zealand might be in a position to turn tuna into wildlife, but tuna as food are a “matter of survival” for Pacific Island nations, says Blaha, the Pacific fisheries consultant. “It’s easy to reject a whole food system because your life doesn’t depend on it,” he says, and quotes the playwright Bertolt Brecht: “First comes food, then comes morality.” The industry directly employs more than 20,000 people in the region, and the governments of Tuvalu, Tokelau and Kiribati derive more than half their national income from tuna fishing licences and access fees. “All food systems have impacts,” Blaha says, “so everything is a compromise.”
Tuna are culturally important worldwide, and are present in a vast swathe of the world’s oceans. They provide jobs, renewable protein resources, and are an integral part of marine ecosystems we’re only beginning to understand. All that makes cautious management essential.
“What we should not be doing is looking at the data and saying, ‘Let’s take the riskiest quota there is because then we can make a little bit more money this year,’” says Nickson. Pew’s “Netting Billions” report into tuna value chains showed, in fact, that catching more tuna can actually result in less money. The collective end value of the seven most important commercial tuna species peaked in 2014, with five million tonnes fetching US$42.2 billion. In 2018, more fish were caught—5.2 million tonnes—but the revenue dropped to US$40.8 billion.
“The overall value of tuna decreased, even though more tuna was taken out of the ocean,” says Nickson. “And it’s a really strong argument for why you want to manage for ocean health and sustainability.”
Some tuna species—including southern bluefin tuna—have been hauled back from the edge of extinction by governments and industries agreeing on and enforcing catch limits, backed up by science, and supported by citizens and environmental advocates. But the relative health of the fishery hasn’t solved other problems—the human-rights issues, the political squabbling, the subsidies, the traceability.
With their wanderings, tuna trace threads of connection across the globe. The migrations of southern bluefin tie New Zealand to Australia, Indonesia and the Pacific Islands. A fish born off Java is caught within sight of the Southern Alps and flown to Japan, while elaborate, murky supply chains link distant-water fleets owned by Taiwan and crewed by Indonesians to Thai canning factories and supermarket shelves worldwide.
These links—and the billions of dollars at stake—force nations to the negotiating table. To save tuna from extinction, to ensure tuna fisheries continue to exist, countries have to meet, cooperate and accept short-term compromise for long-term collective gain.
The benefits of doing so—of letting tuna unite us rather than divide us—may surge beyond healthy fish populations. If it’s possible to save a fishery, can we also expunge slavery from fishing boats? Stop albatrosses swallowing hooks? Improve the health of the oceans more broadly?
The challenges are formidable, but perhaps tuna can show us the way.
July 12, 2021: This story was updated to correct the description of how tuna populations are estimated using muscle tissue samples.