Atlantic Bluefin Tuna: The Forgotten Superpredator

We would expect that a huge, aesthetically pleasing, and ecologically important large predator would be world famous and celebrated in its own right. Especially if it is endangered, has evolved some extreme physiological adaptations, or launches violent, coordinated attacks on prey. However, there is one such species that does not derive any such benefits. 

The Atlantic Bluefin Tuna (Thunnus thynnus). Called the ultimate fish by none other than David Attenborough. Although our perception of tuna is as food, this is a major injustice to this fish. It would be unthinkable to consider tigers or wolves as not being wildlife, even if we ate them as food, but this is the exact plight facing the bluefin. And it is this exact lack of awareness that has led to the the fact this species is known mostly for sushi and being endangered, rather than for being the creature of superlatives that it is.

Few people, even those that care about the fate of the bluefin, know just how awesome an animal it is in life. As a result, people what would otherwise be impressed find it hard to relate to this fish. And that may well be the driving factor behind this species's extinction: lack of appreciation.

This fish has only a few decades, and possibly just a few years, for us to stop its human-caused extinction. My hope is that this doesn't end up being an eulogy to the species, but realistically, it may well become one. Due to this, this post will be among my longest posts to date, to try and write down as much as possible about this incredible animal before its demise.

Above: a giant bluefin nearly 10 feet long dwarfs a scuba diver. Credit to Brain Skerry.

These are truly enormous fish: even today, Atlantic bluefin regularly exceed half a ton in weight and grow over 10 feet in length. Giants (over 400 pounds is considered "large" or giant) like these are much rarer than before, however; a sad side effect of fishing for only the largest individuals.

https://www.youtube.com/watch?v=_VA45L6SXRU

There is a good reason tuna are often referred to as superfish. Everything about them has evolved for peak athletic performance. And even among tunas, the bluefin stands out, having taken these adaptations to the extreme. All organ systems aside from the reproductive system has been changed to enable this fish to be a cut above the rest. This is how you build a swift-moving, high-seas predator.

The body shape matches a teardrop, with the widest part of the body occurring at around 2/5th of the distance from head to tail. This is the most hydrodynamic shape that is physically possible to achieve.

A tuna's main engine is among the most specialized in the animal kingdom. The tail is tall, very stiff, narrow-bladed and swept-back, a form referred to as "lunate". The horizontal keels on the caudal peduncle knife through water as the tail swings from side to side, reducing water resistance and thus the effort needed to beat the tail. The yellow finlets, extending from the like serrations on a saw blade, cut down on turbulence by altering water flow across their surface.

When swimming, tuna make only the minimum amount of side-to-side body movement, and nearly all of the forward thrust is produced by the rapidly beating tail. It's the most energy-efficient way of moving through water. This method of swimming is actually called thunniform swimming, after tuna.

To further streamline the body and make swimming more economical still, most of the fins on a tuna are fully retractable, like the wings of the F-111. The wing-like pectoral fins slot neatly into shallow, cowling-shaped depressions on the flanks, and the first dorsal fin and pelvic fins fold into grooves on the back and underside respectively. These fins are thus kept out of the way during high-speed attacks, but they unfold during tight turns or complex maneuvers for better mobility. The pectorals can also function as a pair of swept-back hydrofoils, allowing the tail to focus on propulsion when the animal is cruising at a moderate pace. 

The remaining fins (the second dorsal and anal fins) are all slender and swept-back, producing as little water resistance as possible. And they have been modified in one other, very crucial way: they are shapeshifting fins. At their bases lie special sinuses filled with fluid, an extension of the lymphatic system. Muscles around this sinus apply hydraulic pressure, which acts on the bones and on fin rays, finely changing the fin's shape and angle as necessary in a particular situation.

https://news.stanford.edu/2017/07/20/tuna-fin-movement-controlled-biological-hydraulic-systems/

Above: a diagram of what makes this predator so competitive in a harsh environment. To see an interactive graphic of this depiction, go to http://ngm.nationalgeographic.com/2014/03/bluefin-tuna/superfish-interactive

Internal physiology of tuna matters just as much as the hardware. As seen in the above diagram, red muscle makes up for a significant part of a tuna’s musculature, a much greater percentage of body mass than in any other fish. White muscle is used for bursts of intense, short-term activity, and red muscle is for sustained activity for long periods of time. With red muscle fibers running down the entire length of their body, tuna are built for endurance.

Bluefin have massive gills and the largest area for gas exchange found in any gill-breathing fish, all the better for extracting oxygen from the water. The gill plates are fixed in place to reduce water resistance: tuna need to swim constantly to breathe. Oxygen delivery has also been improved. Tuna blood contains double or even triple the concentration of hemoglobin compared to inshore fish, and their hearts are several times as large, to pump blood at a high rate. These fish can swim further and faster, and dive deeper, because these adaptations ensure that it takes much more than usual to deprive a bluefin tuna of oxygen.

Yet all that is nothing compared to the most extreme physiological adaptation the bluefin has up its sleeves. While not truly endothermic, all true tuna are able to raise and maintain their body temperature, and it is the bluefin that takes this feature to its zenith. This predator is capable of keeping its body temperature between 77–91 °F in the frigid waters of the North Atlantic, its main hunting grounds. Even the Arctic Circle isn't beyond the reach of the bluefin. In fact, the bluefin is hot-blooded to the point that if it is forced to exert itself for hours at a time, such as being hooked on the end of a fishing line, it can cook itself to death (a dreaded phenomenon called "burn" by commercial fishermen)

The secret to this trick is a specialized countercurrent heat-exchange system, the rete mirabile, that prevents metabolic heat from escaping into the surrounding water. Heat lost from blood leaving the musculature is re-absorbed by chilled, oxygenated blood coming from the gills. This enables the bluefin to keep its brain, eyes, spinal cord, muscles and heart running at high temperatures constantly, enabling quick reaction time and sustained speed in frigid waters. It also enables for faster digestion, enabling the bluefin to more efficiently process and store the calories gained by eating, and to be able to eat again in a short period of time.

Bluefin are fast swimmers, with a maximum speed of 25 miles per hour. This burst of speed is reserved only for times when it's really needed, however, and most of the time is spent at a much slower pace. Normal cruising speeds are only around 5 mph.

While tuna (and other fish also known for high-performance adaptations, such as billfish) have been stated as achieving extremely high speeds of over 50 miles per hour, these are based entirely on non-scientific sources or outdated studies using poor methods. Swimming at over 30 miles per hour would be physically impossible for any animal: cavitation affects body tissues at such speeds, cutting down speed and causing injuries. (For the same reasons, orcas and other cetaceans are much slower than books would have you believe)

In addition to not tiring easily, tuna also recover extremely quickly from exhaustion, in just a matter of seconds. Like other animals, the bluefin resorts to anaerobic metabolism for quick bursts of activity (like the final rush at the climax of an attack), leaving an oxygen deficit. But due to its adaptations, it can recoup this deficit easily and without ceasing to move, enabling it to repeat the process within a short period of time. Because their entire lifestyle relies on being in perpetual motion, taking a rest as most fish do would be fatal.

In short, the bluefin is superbly adapted for outswimming, outlasting, outdiving, outtraveling, outeating, and outgrowing other fish. All are skills critical in the pelagic environment.

There are two breeding populations of Atlantic bluefin: one breeds in the Gulf of Mexico, and the other in the Mediterranean. The species is widespread throughout both these areas, and throughout the North Atlantic. There used to be a third population in the Black Sea, and a fourth off the Brazilian coast, but fishing has killed these groups off.

Until recently it was thought that the North Pacific population of bluefin was the same species, but this population has been reclassified as a separate species, the Pacific Bluefin Tuna (Thunnus orientalis). It's just as much, if not even more, endangered than the Atlantic bluefin, and its migrations are even more spectacular.

Above: Atlantic bluefin swimming near the bottom. Credit to Brian Skerry.

Unusually among tunas, the Atlantic bluefin will often venture inshore and near the sea bed to hunt, usually off the Eastern Seaboard. Most true tuna species stick to places where they can't see the sea floor. Not this one.

But open water, specifically the epipelagic zone (surface to 200 meters down), is still the bluefin's primary hunting ground. While they can dive down to over half a mile deep to track down squid or lanternfish, they don't stay there for long, unlike, say, bigeye tuna (which specialize in rapid, vertical movements and deep diving)

This is a harsh environment where there are few sources of prey and even fewer cover. The pelagic waters of the world's oceans are called "marine deserts" for being barren of life, and this is especially true in tropical waters. The lack of sustenance in clear tropical seas is part of why tuna became capable of controlling their body temperature, in order to penetrate the colder, richer waters in temperate latitudes.

But every desert has its oases, and the open ocean is no exception. The edges of the epipelagic zone, where the high seas meet more fertile coastal waters, are far richer in life. Oceanic islands, as well as submerged sea mounts (underwater peaks), influence currents and are a magnet for large pelagic predators. Upwellings also bring nutrients to the surface and allow for plankton blooms, which attract the plankton-feeding fish the bluefin preys on.

As mentioned above, bluefin are warm-blooded, and so it's not much of a surprise that the cold, nutrient waters of the North Atlantic are their main summer haunts. Areas like the Gulf of St. Lawrence, Gulf of Maine, Georges Banks, and the Azores are therefore reliable places to find these fish, since they turn up regularly each year to hunt.

The deeper waters off the west coast of UK is on its way to soon becoming a bluefin hotspot as well, if recent observations are any evidence (http://blueplanetsociety.org/2015/11/atlantic-bluefin-tuna-new-perspective/)

For the bluefin, and for all hunters that specialize in plying the high seas, survival means traveling vast distances from one of these oases to the next, hunting as they go. Searching for prey is a immense task, but bluefin have a much easier time at it. Why? Because they search in groups.

Above: a pod of bluefin seen from above. Credit to Wayne Davis.

Atlantic bluefin show some of the most complex social behaviours of any fish, since they live and hunt mostly in groups. This social behaviour first manifests when young bluefin are half an inch long, and continues until death. Younger fish travel in large groups: mature adults travel in smaller, close-knit pods of up to 20 fish.

Social dynamics and communication behaviour in tuna is virtually unstudied, but already some interesting observations are being made. One observation that has been known for some time is that bluefin arrange themselves by size. Giants will only live with other giants, juveniles will only live with similar-sized juveniles, etc. This may be to prevent cannibalism in the food-poor waters of the epipelagic zone. However, on occasion, juvenile and small adult fish may hunt alongside the faster, more powerful giants.

Above: Bluefin following a humpback whale. Credit to Wayne Davis.

Younger bluefin also often associate with larger animals like whales, though nobody knows why.

Above: Bluefin following a basking shark. Credit to Wayne Davis.

Above: a lone giant. Credit to Wayne Davis. 

Some large bluefin occasionally break off from their groups, hunting alone.

Above: A typical swimming formation. Note that the fish are placed at equal intervals. Credit to Wayne Davis.

Masters of synchronized swimming, bluefin have an array of formations they arrange their groups into, each of which has a different use.

Swimming in a single file like this reduces turbulence and enables the fish to take advantage of each other's slipstream, saving energy. It's the same reason geese migrate in skeins.

Large adults also often swim in a straight line, called "soldier formation".

Since tuna lack any method of making sounds, they have to rely on visual cues to coordinate with each other. The flanks of a tuna have several set colours and patterns that they can change into, most of which are metallic. An excited bluefin will shimmer in several hues of gold, purple, light blue and silver, switching from one base colour to another rapidly. Iridescent, light-blue vertical bars will also appear and then disappear on its flanks in heated moments.

These colour changes and flashes serve two functions: to communicate with fellow tuna during a hunt or when mating, and to confuse prey. The eyes of many marine fish are especially sensitive to blue and ultraviolet, so it is possible to "overload" the prey's vision using the iridescent blue bars. Rapid, unpredictable colour changes startle the quarry. And these displays can be seen from some distance and are also highly visible to fellow bluefin, so by changing their appearance in a certain sequence, they can coordinate with each other to set up an attack.

Above: Flashing bluefin. Credit to Wayne Davis.

Rolling on their side, or "flashing" (as one tuna is doing here) is an example of this communication.

Above: Hunting formation. Credit to Wayne Davis.

Among the world's pack-hunting predators, bluefin are among the most cooperative and organized. Their knack for teamwork is what makes a group of giant bluefin one of the deadliest predatory forces in the Atlantic.

The typical hunting formation is a series of wide parabolas, with individuals placed at precise, equidistance intervals. It's one of the greatest feats of coordinated behaviour in the world, rivalled only by orca pods and crocodilian hunting assemblies. Other tuna also hunt in formation and communicate with visual signals, but none are as meticulously organized as this.

When prey is detected, the tuna work as a team to sweep the prey into one of the parabolas, then close ranks to encircle their victims. Like a net cutting off escape routes, the arms of the parabola formation wrap around the school of baitfish, leaving no exit.

https://link.springer.com/article/10.1007/BF00692374

Small fish are the mainstay of the bluefin's diet, and they have a method of hunting that is common among many open-water predators: forming a bait ball.

The best defence for schooling fish is confusion. By synchronizing their movements, and travelling in immense shoals, species such as herring and mackerel make it nearly impossible for predators to lock onto and isolate a single individual. There is also the advantage that the greater the numbers of prey, the less likely that a given individual will be eaten.

Bluefin (as well as other tuna species and many other marine predators), however, turn this defensive maneuver against their prey. By cutting out a large section from the main shoal using the arms of the parabola formation, they end up with a smaller group of fish whose movements they can control more effectively. The tuna then relentlessly attack this school from below and from the sides, causing them to travel up to the surface, where they can't escape. 

Corralling the fish in this manner forces them to press tightly together. Now there is no reason to identify single individuals, because any attack on the bait ball would ensure at least one fish due to the density of prey. The bluefin take turns rampaging up through the bait ball until the entire ball has been consumed. Then they rearrange themselves in the parabolic formation, return to the main shoal of prey, and repeat the whole thing.

If you want to know just how insanely violent bluefin tend to be when attacking live prey....well just take a look at this gif and the ones coming up. "Feeding frenzy" is the best term but doesn't really cover it, since each fish is massive.

Above: Bluefin attacking a massive herring bait ball. Credit to Wayne Davis.

In the North Atlantic, several fish species stand out as prey for bluefin. Herring and mackerel are both abundant and fat-rich, the perfect meal for an active predator that burns a lot of energy. In recent years, however, stocks of herring have started to decline, which may be a minor factor in the plight of the bluefin.

Sand eels are also eaten if they are available: unlike herring or mackerel, these are rarely herded to the surface, but devoured at depth.

In deeper water, bluefin may also make near-vertical dives to feed on squid.

Above: a giant bluefin flashing as it hurtles towards a prey fish on the surface. Credit to Carl Safina.

Above: "The Chase". The best sequence of a bluefin tuna making a kill ever taken.

Larger prey may also be consumed, and bluefish are a special favourite. Normally these two species are competitors for the same prey, but bluefin get large enough to swallow an adult bluefish in one gulp.

A recent development in the Gulf of St. Lawrence is that the bluefin who migrate there annually have learnt to follow commercial fishermen. They pick off herring and mackerel that fall out of the nets.

Video here (along with guest appearances by pilot whales, also eating the herring): https://www.youtube.com/watch?v=wM6UU45EMnY

Bluefin feeding in this way have learned to check for fishing tackle before eating a dead or dying fish, making many close passes before actually eating. These animals are not mindless and learn by experience, as well as by watching others. As a result, most anglers have been resorting to using live bait and lighter line.

However, the view of this species as a predator of other fish and squid might be only part of the story. Even though most images, like this one, show bluefin eating fish, jellyfish make up a surprisingly high proportion of their diet in the Mediterranean (up to 80% in juveniles and 60% in adults, though these are unusual cases). Jellyfish are poor in nutrients, so may appear to be a poor dietary choice, but they are common and really have no defences against something as mobile as a bluefin. 

This is not to say that the bluefin's skill as a bait ball specialist has been overblown (since it wouldn't need such complex hunting tactics if it didn't use them). It seems that while bluefin tuna are still primarily fish-eaters, they will opportunistically eat whatever prey that is most common in a given area, and in the Mediterranean, that often happens to be jellyfish.

Sadly the declining numbers of bluefin (and other large predators) has led to an overpopulation of jellyfish as well as of small prey fish, disrupting entire marine ecosystems. In fact many marine ecologists warn of "a gelatinous future" if jellyfish continue to increase as they are now.

http://yalikedags.southernfriedscience.com/declining-predators-eat-mediterranean-jellies/

Highly visual animals, Atlantic bluefin tuna rely almost entirely on their large eyes to search for prey. This means they are restricted to hunting where there is visible light, with the twilight zone being as deep as they can go.

Above: When predators team up: giant bluefin tuna hunt side-by-side with common dolphins and some shearwaters. Full video: https://www.youtube.com/watch?v=XzZhSl_00pI

The feeding activities of tuna benefit many other predators that aren't as skilled at hunting groups of small, schooling fish. Species that cannot form their own bait balls often follow bluefin, hoping to crash the party.

Dolphins do have the skills to round up their own bait balls, but they cannot travel as far or as deep as tuna can. So they often travel alongside tuna, hoping that the latter can drive prey further below into shallower depths, at which point both predators work to round up the prey. Tuna also benefit from this arrangement and often shadow dolphin superpods, since dolphins can search a far wider area thanks to their echolocating abilities. 

Some sharks also follow tuna (and dolphins). Like the dolphins, they are capable of forming their own bait balls, but the more predator species there are in one group, the more more likely the chances of victory. A multi-species pack like this is surprisingly common in open oceans worldwide, and it's always a sight to behold.

Above: Shearwaters join in on a bluefin hunt.

Seabirds, however, are the greatest beneficiaries of tuna hunts. Paradoxically, most pelagic birds spend the majority or even all of their time at sea on the wing, rather than on/in the water. Most can only dive to a certain depth to catch prey and a few species are unable/unwilling to swim at all. So they rely on the activities of underwater predators to bring their prey to the surface. 

Tuna hunt in large groups that can easily be seen from the air, and they almost always create bait balls that they trap against the surface. This brings the prey fish within reach of plunge-diving birds, and when the feeding frenzy reaches the surface, it enables even those that cannot swim to pluck fish from the waves.

In fact, many seabirds (especially in the tropics) are entirely dependent on large tuna species to bring them access to prey. Most of the time, this means yellowfin tuna, but in northern waters only bluefin are around to do the job. Loss of tuna, or even a worldwide reduction in tuna numbers, would mean certain extinction for these birds.

Of course the birds (the ones that can swim at least) do take a risk when they plunge into water with such a large, formidable predator. While bluefin are not normally bird-eaters, they may eat birds by accident during a frenzied assault on a bait ball, and it's likely that large adults include any swimming animal small enough to swallow as "dinner".

The above incident, which went viral, took place when an estimated 900+lb bluefin entered a marina, and people started to feed it. A seagull grabbed the fish just before the tuna did, but it was already in the process of opening its mouth and engulfed the unfortunate bird.

Above: a pod of false killer whales carve up a 800+lb bluefin, a rare catch for any predator.

The Atlantic bluefin doesn't have to worry much about being eaten itself, at least after it survives the perils of childhood. Very few animals can prey on adult bluefin. Their massive size and strength, combined with their speed, make them hard to catch and even harder to overpower.

The Mediterranean population of orcas has a unique hunting culture that specializes in small bluefin. Working in groups, they pursue single fish to exhaustion. But this only works with small tuna less than 40 pounds in weight: adult bluefin can outrun the orcas or outlast them in a battle of attrition. Similarly, great white sharks, which also rely heavily on tuna, are limited to making stealthy midwater attacks under cover of darkness.

There are, however, two predators that can kill even large bluefin in broad daylight: the False Killer Whale, and the Shortfin Mako Shark. Both animals are as large as or larger than adult bluefin, meaning they have the strength to take one down, and both share the warm-bloodedness of bluefin. Neither species feeds heavily on bluefin, however (though the shark could if more bluefin were around).

False killer whales hunt in groups, using teamwork to isolate a lone individual, then brutalizing it for hours on end. The mako, on the other hand, uses speed and finesse, slicing off the tuna’s tail to cripple it (and preventing it from breathing at all) before swooping back for the fatal blow.

Truly epic migrants, Atlantic bluefin, especially those from the western stock, make transoceanic voyages almost on a routine basis. Both the western and eastern populations migrate to the other population's home waters on feeding trips, ranging far and wide in search of prey. Some fish have been recorded making repeat crossings. 

The details of bluefin migrations were a mystery for many years. Most people assumed these fish were migratory and travelled far, but they severely underestimated the distance (see below). The use of pop-up satellite tags (or PSAT tags) in the 1980s, which could record travel data before detaching from the fish, changed all that.

Above: The forehead of a bluefin tuna, right where the pineal window is. Credit to Brian Skerry.

How these fish navigate, with great accuracy, over such long distances is still being studied. Bluefin possess a pineal window just above the forebrain, and it is thought that this enables the tuna to sense changes in light conditions rapidly. But other cues such as magnetism, current patterns, and landmarks must also play a role.

This long-distance migration has huge implications. The International Commission for the Conservation of Atlantic Tuna, or ICCAT, has a line (called the ICCAT line) that is used to separate the two bluefin populations. The idea was that fish from one side of the Atlantic stayed on that side, with the populations meeting only in the Mid-Atlantic. By counting fish caught in the western half as part of the western population and vice versa, ICCAT gathers population data, which it uses to determine how large each population is and whether it is stable, growing or declining.

Of course, as we already know, this is wrong: bluefin completely ignore the ICCAT line and routinely cross the Atlantic, so place of capture says nothing about the population a bluefin belongs to. The line accomplishes nothing more than provide false statistics, by mistakenly counting fish from one part of the Atlantic as being born in the other part just because said fish was caught there. However, the ICCAT line is still being used, despite having been outdated for decades. Scientists working as ICCAT consultants have repeatedly urged the organization to stop using the line (and to reduce/stop bluefin fishing in general), but the agency hasn't listened. 

ICCAT is so infamous for going against its scientific body that it has been called "the International Conspiracy to Catch All Tuna" instead. It's said in jest, but this is much closer to what actually happens at ICCAT meetings, rather than what ICCAT is supposed to do. This is the tragic reality for bluefin conservation.

http://www.pewtrusts.org/en/research-and-analysis/fact-sheets/2012/10/05/improving-the-count-of-western-atlantic-bluefin-tuna

Above: Spawning formation. Image courtesy of NOAA. This is likely the only image of bluefin doing the deed.

Spawning takes place in spring from late March to May, but mostly in April. The event often occurs at night.

The tuna shoot up towards the surface in formation. The surface of the ocean lights up as the bluefin flash past in pairs or small groups, releasing eggs or sperm with each pass. Sometimes males and females actually swim belly to belly as they push out their progeny. Soon the sea turns opaque with reproductive cells, understandable given that each large female can produce up to 30 million eggs. The larger the female, the more eggs she produces, and therefore giant females are critically important for the health of the population.

In around two days the eggs hatch. Larval bluefin are tiny, only around 3-4mm in length. At this size they are unable to swim and must drift with the current, feeding on other plankton. They are vulnerable to almost anything, including the small fish their parents prey on. 

But by the end of the year, the situation would be completely reversed. The turbo-charged, superbly adapted physiology of the bluefin enables for rapid growth. The young literally grow one millimetre a day, and within one week develop the muscles, fins and general body shape of their species. And when twenty-five days old, they start to migrate and seek out company, and are half an inch long (more than twice their length when they first hatched). This is, however, still a much slower rate of growth than other tuna species.

The western population grows more slowly, and matures later, than the eastern population.

Above: a Phoenician coin depicting a bluefin tuna.

In the relationship of our species with marine life, the bluefin holds a truly special place, because it was the first marine megafauna to be exploited as a food source by humans. Even in the Stone Age, when humans were first causing species extinctions worldwide, bluefin were hunted in Europe whenever they came close enough to shore, as evidenced by cave paintings. Early Iron Age archaeological sites on the Iberian Peninsula often contain bluefin bones. 

The Phoenicians then developed a method of hunting these fish that is still in use today, known as the matanza or the tonnara. Using a series of fixed nets that intercepted the migrating tuna as they followed their traditional routes in the Mediterranean, they herded the fish towards the inner court, where they were killed in a bloody chaos of foam, muscle, and knives. The Roman Empire also harvested bluefin tuna in this manner, and stored its flesh by drying it, using it as war rations.

Above: a tonarra. Note the unfortunate ocean sunfish that also got trapped with the bluefin: it will likely be killed and discarded.

Large-scale commercial fishing for bluefin is a much more recent development, owing to Japan. And as everyone reading this probably knows, it led to the current, sorry state of this species. The story is far too complex for me to tell here, and deserves a book of its own, but here is an overview:

Despite the Japanese justification that "eating bluefin is a tradition and should be our right", bluefin tuna became popular food fish only relatively recently, in the 1970's. Japanese companies exporting electronics and other goods to the US and Canada hoped to return with something that could be imported and sold in Japan, and Atlantic bluefin tuna (which was then a sportfish that was just killed and discarded in fishing tournaments) seemed to be the thing. With successful marketing, the market exploded overnight, and quickly spread to include the Pacific bluefin (then still considered the same as Atlantic bluefin) and the Southern Bluefin Tuna (Thunnus maccoyii), which lives in the Southern Ocean and as far north as Australia and New Zealand.

Nowadays, bluefin of all three species are sold for truly exorbitant sums, each fish costing around double that of an equivalent mass of silver; the most expensive fish ever was a Pacific bluefin, sold to the highest bidder for over $1.7 million. The problem with these displays of commerce is not only that they are legally selling an endangered species, but also that they continue to reinforce the idea of bluefin tuna as a luxury dish, and not as an endangered species or an animal.

In fact, the Japanese corporation Mitsubishi is buying bluefin tuna by the ton and storing them in huge underground freezers, thus trying to make all three of the species go extinct on purpose. This might sound idiotic, but there is a sinister method to the madness. By causing the bluefin to go extinct, and stockpiling tens of thousands of their bodies in edible condition, Mitsubishi is hoping to make the price of bluefin skyrocket even higher while controlling the global supply. The benefit to Mitsubishi is, of course, that it makes a huge amount of profit from this. It's a truly callous and unthinkable act: to deliberately hope for and cause the extinction of not one but three species for money. Mitsubishi has defended itself by stating that all the tuna it buys are sourced sustainably, but this is simply a lie to save face. There is no such thing as sustainably caught or farmed bluefin and there might not be in the future.

http://projectcensored.org/mitsubishi-profits-worlds-tuna-become-critically-endangered/
http://www.independent.co.uk/environment/nature/revealed-the-bid-to-corner-worlds-bluefin-tuna-market-1695479.html

Besides the legal fisheries, there is also a huge amount of illegal fishing activity that goes ignored by ICCAT despite the evidence. Many nations in the European Union profit from illegal fishing, and therefore they are unwilling to provide legal reinforcements, or restrict the legal fishery.

Finally, in the Gulf of Mexico, large, breeding bluefin are frequently killed as bycatch on longlines seeking other species. Since this takes place in the spawning season, the effect is devastating to the western Atlantic population.

The result of all that is, of course, that the Atlantic bluefin is endangered. It's given the Endangered rating by the IUCN, which is the same rating as a tiger, and one rating above the giant panda. And considering the lack of protection for bluefin and the fact being ignored is a big part of this problem, it's likely that the species is actually in far greater jeopardy than the tiger (which is really saying something, since tigers may not survive this century).

Nor does the slaughter stop at just one species. Pacific bluefin populations have declined even more precipitously. And in the Southern ocean, the southern bluefin hasn't escaped the fate of its northern sisters, and is classified as Critically Endangered, as close as it gets to extinction without being actually extinct.

While the number of individual bluefin for all three species are still relatively high, this is deceptive. Most of these are very young fish that will die before they ever get a chance to breed. The demographic that really matters are breeding adults and juveniles that become breeding adults: and there are far fewer of them than there should be.

http://www.nytimes.com/2010/06/27/magazine/27Tuna-t.html

Exacerbating the issue has been the fact there are many (mostly the fishing industry, but also some independent scientists) who claim the situation isn't as dire as it appears, either because there is an undiscovered third population out there or because the two populations we know of are stable/recovering. Both of these arguments are debatable at best and downright false at worst, but they have been leading many members of the public, especially recreational anglers, to become complacent. Even NOAA is divisive over this: some of its independent biologists have published a study that claims a third population does exist, while the majority are skeptical and have pointed out why said study's own data contradicts its conclusions. (disclosure: I follow the second view due to it having far more support)

I have argued with recreational anglers online who have killed Atlantic bluefin, and been attacked by them. They state that because it's (supposedly) only the Pacific and southern species that are still in trouble, it's acceptable to harvest Atlantic bluefin as long as it remains within legal quotas. Said legal quotas are likely to be far too optimistic, however.

Here are the only well-intentioned people I know of that are stating that the situation isn't as bad as it seems (actual scientists, not industry advocates...though who knows?)

http://tunalab.org/documents/PEWtuna-best-available-science-atlantic-bluefin.pdf

http://tunalab.org/documents/ResponsetoPEWfactsheetfinal.pdf

And here are the counterpoints that, for the most part, debunk their arguments.
https://medium.com/carlsafina/bluefin-tuna-new-study-doesnt-hold-water-6aa066d036f7

http://www.pewtrusts.org/en/research-and-analysis/analysis/2014/10/13/an-uncertain-recovery-for-atlantic-bluefin-tuna

http://www.pewtrusts.org/en/research-and-analysis/blogs/compass-points/2017/09/29/has-eastern-atlantic-and-mediterranean-bluefin-tuna-recovered-not-yet

http://www.cbc.ca/radio/thecurrent/the-current-for-october-11-2016-1.3798971/conservationists-fear-surplus-of-atlantic-bluefin-tuna-does-not-equate-to-healthy-stock-1.3798980

Above: Spawning area for the western population of Atlantic bluefin vs. the extent of the oil spill. 

The 2010 Deepwater Horizon oil spill did no favours for bluefin either. The western population of Atlantic bluefin breeds in the Gulf of Mexico, and as mentioned above, these fish spawn in April....which is exactly when the oil spill took place. Cleanup efforts also backfired. The surfactants used to clean up visible oil (so it would appear that environmental issues were being addressed) are not only toxic in and of themselves, they spread the oil into the water, worsening the situation for aquatic species.

http://www.nmfs.noaa.gov/stories/2014/02/2_13_14oil_fish_hearts.html

http://www.pewtrusts.org/en/research-and-analysis/analysis/2014/04/18/bluefin-tuna-four-years-after-the-deepwater-horizon-oil-spill

Above: Breaking the surface. Credit to Carl Safina.

The bluefin doesn't have time on its side: its extinction is likely to take place within this century if things don't change. So what are the solutions?

Some have claimed aquaculture as a solution. All three species of bluefin have been bred in captivity (though the process is too complicated to get into here).

However, farming bluefin tuna comes with new problems to solve. For starters, the food. Remember that bluefin are high-octane fish that never stop travelling. It takes 15 pounds of fishmeal to produce 1 pound of tuna. In other words, it would actually require that we overfish the seas just to feed farmed tuna. This problem could be averted if we switched to plant-based fish food, but it is not clear if tuna can live on such a diet, and again, the input is much greater than the output, making tuna farming a vast waste of resources.

And it's possible farming may reduce the population of bluefin. Most tuna "farmers" are actually ranchers in the Mediterranean who catch large numbers of small fish, fatten them up in pens, and then slaughter and sell them. The reason for this is that bluefin catches are measured in tons, and not number of individuals, so by catching small fish the ranchers can sell far more fish than otherwise. Breeding the fish is an expensive process that tuna ranchers would be unable or unwilling to follow, and therefore, the majority of bluefin "farms" would actually be taking fish from the wild population even if large-scale captive breeding was feasible.

Most tuna farmers and ranchers lie about how many fish can be sold in one year, leading to exaggerated statistics about how feasible tuna aquaculture is. As a result, we seriously have to doubt whether farmed bluefin will ever be able to meet the demand.

Finally, there is the ever-present risk that captive-bred or ranched individuals may leak into the wild, and cause a direct decline of the wild population. Unless taught how to survive in the wild, or released at an age where they have time to learn from experience, animals raised in captivity behave differently than those born in the wild, due to inexperience. Farmed fish tend to be bold, aggressive eaters due to having to compete for food at feeding time, and because they are fed regularly, they are larger. At the same time, they lack the experience needed to survive independently of humans. So if bluefin escaped from aquaculture facilities (or were intentionally released to restock the Atlantic), they may bully or even cannibalize the wild population only to die themselves, leading to a net loss of bluefin. This has happened with many species of trout and salmon, so there are clear precedents for farmed fish causing a decline of their wild counterparts.

http://www.stockholmresilience.org/research/research-news/2014-09-11-out-of-tune.html

https://nomadicecologist.wordpress.com/2015/08/01/farmed-bluefin-tuna-a-luxury-we-cant-afford/

The Atlantic bluefin is a famed sportfish, and has been considered so long before the advent of the Japanese sushi market. Anglers pay a lot of money to fish for this species: could the recreational angling lobby prove to be an ally in the fight to save the bluefin?

It's happened before: one of the groups working to solve the aforementioned by catch problem in the Gulf of Mexico is the International Game Fish Association, the world's largest angling organization. https://voices.nationalgeographic.org/2013/03/20/the-bottom-line-coming-together-for-bluefin-tuna/

Nonetheless, there are some real concerns around recreational angling, such as removal of large breeding adults from the population, post-release mortality caused by stress and fatigue, and the impact capture and release has on female fish, which may reabsorb their eggs and skip breeding as a result. Another problem is the fact many (though far from all) anglers want to take bluefin to sell to the Japanese market, which defeats the whole purpose, if not worsen the problem.

And then there is the fact hunters and anglers tend to focus only on their target species. They want more animals to hook or shoot at regardless of how many there are supposed to be. While it may seem stupid to worry about there ever being too many bluefin, this is what happened to white-tailed deer: it went from nearly extinct to very overpopulated. We don't want other species to die out or decline as a result of our efforts at saving the bluefin.

Perhaps a diving industry could save bluefin, but again, the problem is that few people know how awe-inspiring this fish is when seen in real life. Due to this issue, there is no ecotourism industry around seeing tuna as there are for sharks or whales. It's a real shame, IMHO, since bluefin tuna are exactly the type of animal divers would pay money to see. In fact, bait balls and feeding frenzies involving tuna are considered a major attraction by seasoned, adrenalin-seeking divers.

To any scuba divers who see this, I recommend that you read this article by Alert Diver, a global diving magazine: http://www.alertdiver.com/Tuna-Super-Fish

http://proof.nationalgeographic.com/2014/02/26/brian-skerry-swimming-with-giants/

Probably the best, though among the hardest, option is to simply realize that the Atlantic bluefin is a wildlife species and not just a food item, and that it's an endangered wildlife species that is almost impossible to manage in a sustainable fashion due to its behaviours. Treat it as a part of its ecosystem, and not as a commodity.

This is the same thing that happened to whales and is happening to sharks. Whales were once considered food items or sea monsters, but nowadays they have so much public support and good PR that it's actually posing problems for other species (including, ironically, sharks and bluefin tuna) that are neglected or looked down on due to these attention/money hogs. Similarly, sharks are finally starting to gain major public support, with the last two Shark Weeks being less sensational and more based on genuine science, and with their intelligence and sophistication becoming increasingly better known.

Like whales and sharks, the Atlantic bluefin tuna sits high in the marine food web, and like them it is huge, powerful, intelligent, and evocative. If more people realized the parallels, perhaps more people would support this species. 

And it's not just bluefin tuna: there are plenty of marine animals, from swordfish to giant squid, that also meet the criteria, even though not all of them are threatened. All of them deserve to be placed on the same pedestal we place the predators of the land and the air on. Few if any of them have been.

If the bluefin wasn't a fish, we wouldn't even be having this conversation. The only reason it's being traded, legally, to the point of extinction is because it's a fish, and people do not tend to consider fish as wildlife.

But maybe there is still a window of opportunity left, albeit a rather small one. Maybe, just like we have done before for two other groups of animals, we can accept not just the bluefin but large, oceanic predatory fish in general, as being worthy of existing.

Many people associate spiritually with large, spectacular land animals, as well as marine mammals and even sharks. Why not the bluefin? http://www.saysomethinguplifting.com/2014/10/connecting-with-tuna/

The challenge is this: can we stop eating this species altogether? Can we learn to recognize it for what it truly is? There isn't any way (at least at the moment) to eat any species of bluefin tuna without having a major impact. And even if there was, I doubt people who genuinely knew about bluefin would eat this species. It would be like eating a lion, an orca or a golden eagle....except those three options are far more environmentally friendly than eating a bluefin tuna.

The Atlantic bluefin is a marvel of evolution, and an extreme example of just how cutting-edge an animal's adaptations can be for surviving in one of earth's harshest, most competitive environments. Yet all of these adaptations, which hold great promises in biotechnology developments, are being swept aside as the general public still sees this animal as an expensive food item, or at best an endangered expensive food item.

It's far past time for that to stop.

Above: Bluefin in the Gulf of St. Lawrence. Credit to Brian Skerry.

To make the ending less pessimistic....some resources.

Here is a good National Geographic article on bluefin tuna biology and conservation: http://ngm.nationalgeographic.com/2014/03/bluefin-tuna/brower-text

Superfish: Bluefin Tuna is, as far as I know, the only documentary that focuses on the natural history of the Atlantic bluefin, as well as some notes on research and conservation. It's even narrated by David Attenborough! Read more at http://tvblogs.nationalgeographic.com/2012/04/10/superfish-bluefin-tuna/

To see more animal profiles, visit r/creatures_of_earth.