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Bluefin Tuna at Risk

Sustainable Aquaculture May Have the Solution


Wild-captured Atlantic bluefin tuna raised in a cage in Spain.   ©TunaTech GmbH (Germany)
Wild-captured Atlantic bluefin tuna raised in a cage in Spain. ©TunaTech GmbH (Germany)

The Strait of Gibraltar—where the Atlantic Ocean pours into the Mediterranean Sea—is so narrow that on a clear day the African coast is visible from the small fishing community of Barbate, in the southern Spanish province of Cadiz.


For millennia, fishermen have hunted this water for Atlantic Bluefin tuna as the massive fish funnel through this thin gap between continents towards their spawning grounds each spring.


These powerful, swift, deep-diving fish were once so plentiful the waters teemed with them. But severe overfishing in the 20th century pushed their populations into danger zones by the 1970s.


Since that wake-up call, government bodies have worked in tandem with their foreign counterparts to save a species of fish that crosses countless international boundaries in its lifetime.


Today, decades of conservation efforts, such as fishing quotas and limits on fishing techniques, have helped the Atlantic Bluefin tuna rebound, according to the International Union for Conservation of Nature (IUCN). However, the Southern Bluefin tuna remains “endangered,” and the Pacific Bluefin tuna is “near threatened,” the IUCN says.


And now there are efforts to sustainably “ranch” and “breed” these fish, which normally reach weights of hundreds of pounds.


Ancient Tuna Fishing


Centuries ago, Phoenician fishermen were the first to set up the “Almadraba,” a netting system using boats that is still practiced today.


Victim of a trawling net.   ©Christi_j/Pixabay
Victim of a trawling net. ©Christi_j/Pixabay

The Almadraba-style corralling of thrashing bluefin, their giant bodies smashing against each other in a futile attempt to escape, turns the churning waters slowly to pink, then red. Such a sight might seem barbaric, but it is arguably more ecologically beneficial than the high-tech trawlers that track nearby shoals and drop huge nets that gather up everything in their wake. At least the ancient netting method allows juvenile fish to escape, grow, and propagate, ensuring the survival of the species.


The worldwide appetite for tuna sushi, sashimi, or simply steak wasn’t always there: Tuna was once viewed as a gamefish to be caught for sport.


But then tuna meat became popular fare in Japanese sushi restaurants, and now several species face unquenchable global demands for their delicious cuts of meat. Case in point: One tuna can fetch as much as $30,000 at Tokyo’s Tsukiji market, the world’s largest seafood market.


Tuna sale at Tsukiji Fish Market.   ©Fisherman/Wikimedia Commons
Tuna sale at Tsukiji Fish Market. ©Fisherman/Wikimedia Commons

Quotas and Other Fishing Controls


Still, if all three types of Bluefin—Atlantic, Pacific, and Southern—are to survive, they will need to be fished using modern, sustainable methods that allow their numbers to climb.


The introduction of international fishing quotas for all varieties of bluefin, radically reducing the catch of smaller bluefin, and limiting the number of adult tunas fished, has helped the numbers rebound.


In 2017, the Western and Central Pacific Fisheries Commission and the Inter-American Tropical Tuna Commission agreed to work together to replenish the Atlantic and Pacific Bluefin tuna populations to 20% of their historic levels by 2034, National Public Radio reported. Currently, the Pacific tuna stock is less than 3% of what it once was.


Kevin Piner, research fishery biologist at the US National Oceanic and Atmospheric Administration (NOAA) Fisheries’ Southwest Fisheries Science Center, led a recent Pacific bluefin assessment that shows promising results. “The new findings demonstrate the resilience of a species that can multiply quickly when given the chance,” he said. However, more sustainable methods will be needed to satisfy demand and keep fish stocks high.


'Ranching’ Tuna


In the middle of the Mediterranean, over 1,000 nautical miles from the nets of Barbate, the small island of Malta lies close to the spawning grounds of the Atlantic bluefin.


Unsurprisingly, this is the heart of commercial fishing in the region and where scientists are using a more sustainable approach to bluefin fishing called “ranching.”


This method, imported from Australia, involves capturing juvenile tuna in the wild and transporting them to large pens where they are grown to market size. Ranching accounts for one third of the Atlantic bluefin quota, up to an incredible 14,000 tons of fish per year.


Ranching, where juvenile fish are captured in the wild and grown to market size, makes up a third of the Atlantic bluefin quota, up to an incredible 14,000 tons of fish per year.

There are two concerns over the future of tuna ranching. First is the taking of young bluefin from the wild; the second is feeding them wild-caught bait fish.


Malta’s docks are now home to numerous refrigerated containers full of frozen bait fish. Every day, twenty-seven containers full of fish are thawed and supplied to the fish farms—each has up to thirty cages brimming with ravenous fish.


‘Breeding’ Bluefin Tuna


The ranching practice is considered unsustainable by many, so scientists in Malta have been working to replicate a technique discovered by their Japanese counterparts over a decade ago—breeding tuna from an egg.


The Japanese process has been successful—over 3,000 tonnes (2,952 tons) of Pacific Bluefin tuna have been grown through this type of aquaculture. But, so far, Japan is the only country to make it work commercially.


Three-day old bluefin hatchling from larvae, ready to live on live feed, raised by Tunatech in hatchery in Malta.   ©TunaTech GmbH (Germany)
Three-day old bluefin hatchling from larvae, ready to live on live feed, raised by Tunatech in hatchery in Malta. ©TunaTech GmbH (Germany)

In Malta, Professor Chris Bridges and fellow scientists from across the Mediterranean have recently perfected a technique to do the same with the Atlantic variety. All they need is financial backing to make the scheme commercially viable.


“Everybody has the same idea: We want to domesticate and breed the bluefin tuna. We know it is possible. Japan has shown us the way, in terms of what they have done, and now it is just a match of getting the right mix of investment together with technology, pushing this thing forward,” says Bridges.


Professor Bridges—part of the team for over a decade at the aquaculture life sciences company, TunaTech—explains how the new method will revolutionize tuna fishing in the Mediterranean: “Basically, we can short-circuit the whole system of ranching and replace it with seed, as in other aquacultures, making it totally sustainable, as you won’t need to fish the wild population.”


He adds: “We can produce as many eggs as we need for the full cycle. The fish that are caught in the spawning areas will still spawn in captivity with anything up to 300-400 spawning fish, meaning that we can collect 70 million eggs every day—a whole dustbin full of them!”


Prof. Jeff Bridges holds approximately 10 million freshly collected bluefin tuna eggs.   ©TunaTech GmbH (Germany)
Prof. Chris Bridges holds approximately 10 million freshly collected bluefin tuna eggs. ©TunaTech GmbH (Germany)

The next step will be to create a hatchery. “With a hatchery, a brood stock would be used continually over the next three-to-four years, which would mean we would only have to take approximately 100 fish out of the wild population. Then, we produce fingerlings [juvenile fish] which could be grown out to any sized fish. You can grow a five-kilogram (eleven-pound) tuna roughly in less than one year.”


The other half of the sustainability equation is getting rid of those refrigerated containers on the Maltese docks. By current estimates, demand for the fish meal they contain will exceed what can be collected from the sea by 2050.


Emerging Solutions


A new plant-based type of feed known as “tuna sausages”—a mixture of soya and fish protein—has been fed to ranched fish as an experiment. After a few weeks, the ranched fish were successfully weaned off the bait fish.


Professor Bridges assures me that in Japanese trials of “green” tuna, the flavor of the fish was unaffected. The task now is to get the cost of land-based protein—which could come from any number of sources from insect protein to chicken feathers—down in price to match the cost of its fish meal competitors.


“The world population is growing, and there is no way we can continue to provide protein and food through fishing,” Professor Bridges says. “That’s the reason we favor aquaculture, as this is the only way to harness the oceans.”


“If we can go to Mars,” he adds, “we have the technology to work in the ocean.”


Aerial view of TunaTech brooding cage holding about 50 adult fish. In top left corner is an egg-collecting net—attached to cage exterior—through which the eggs are collected. In the center is a small feeding chamber.   ©TunaTech GmbH (Germany)
Aerial view of TunaTech brooding cage holding about 50 adult fish. In top left corner is an egg-collecting net—attached to cage exterior—through which the eggs are collected. In the center is a small feeding chamber. ©TunaTech GmbH (Germany)
 

*Gordon Cairns is a freelance journalist and teacher of English and Forest Schools based in Scotland.


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