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Requiem for a Fish? The Atlantic Bluefin Tuna


“The oceans are the planet’s last great living wilderness, man’s only remaining frontier on Earth, and perhaps his last chance to prove himself a rational species.”

John L. Culliney, author of Islands in a Far Sea.  Nature and Man in Hawaii

In recent posts I have been writing a lot about climate change.  This blog is about the whole environmental crisis and it’s important to not neglect those other aspects – overuse of resources, pollution, and so on.   And so I turn to overfishing, and to one of the most magnificent fishes in the sea: the Atlantic Bluefin Tuna, Thunnus thynnus.

Exquisite Magnificence – the Tiger of the Sea

At four meters in length and 500 kilograms weight, the Atlantic Bluefin is one of the largest fishes in the sea, and an animal seemingly designed for sheer speed and beauty.  The largest ever recorded was a 4.5 meter long specimen, and the heaviest ever landed by a sport fisherman was a 678.58 kg fish caught off Aulds Cove, Nova Scotia, Canada in 1979.  (There is an earlier report of a 787 kg fish caught in the Black Sea.)  If engineers set out to build an efficient open-ocean fish they would have difficulty improving on the Atlantic Bluefin (and if the Bluefin did not exist, their imaginations would probably leave them far short of realizing anything like it).  Its overall body shape from its inflexible, streamlined snout to its narrow, rigid peduncle supporting a large, high aspect ratio tailfin maximizes its passage through the water.  The tiny finlets between the dorsal and anal fins and the tail, as well as the arrangement of scales over the widest part of the body minimize turbulence and drag.  It even has little slots into which it stows its dorsal and anal fins, and shallow depressions on its sides in which to house its pectoral fins, when swimming at speed.  And it is fast, very fast — the Atlantic Bluefin is variously reported to cruise at 1.5 to 4 knots, to cruise at 10 to 20 body lengths per second, to maintain 8 knots for significant periods, and be capable of burst speeds of 20 knots (converting knots, that’s 3 to 7, 15, and 37 km per hour respectively, while the body speed estimate could represent 72 to 144 km per hour for a 2 meter fish).  Its close relative (and very similar in size, shape and biology), the Southern Bluefin, Thunnus maccoyii, has been clocked at 75 km per hour.  Lists of the 10 fastest fish put bluefins ahead of other tuna but behind wahoo, marlin and sailfishes.  Sailfishes and cheetahs can do 112 km per hour; we manage 27.

Atlantic Bluefin Tuna
(photo from National Geographic site)

The Atlantic Bluefin swims continuously, as do all tunas.  In evolving its aerodynamic shape, it has lost the ability to pump water over its gills and must move forward to ram water through its open mouth.  It is an exceptionally efficient swimmer because in addition to its streamlined shape it is one of the very few warm-blooded fishes.  This feature, unique to the tunas and billfishes, relies on the simple fact that muscular contractions generate heat.  By routing the blood vessels from the gills (where blood is inevitably cooled to ocean temperature) not through the center of the body as in other fishes, but via vessels close to the body surface, this cool but oxygen-laden blood does not cool the core of the fish.  Furthermore, blood is then carried down into the muscle mass on each side of the fish, and, by means of an intricate arrangement of closely intermingling incurrent and excurrent vessels, this cool blood ‘captures’ the warmth in blood emerging from the muscle in adjacent excurrent vessels, effectively keeping the heat trapped within the muscle.  As a consequence, the Atlantic Bluefin keeps its body temperature between 28o and 33oC while swimming in water ranging from 7o to 30oC.   Incidentally, similar ‘countercurrent’ exchange systems of blood vessels in the upper legs allow ducks to stand around on the ice without getting cold (other than their feet), and no, ducks are not particularly closely related to Bluefin tuna – they just discovered the same plumbing trick.

Drawing of the Atlantic Bluefin from EU Commission site.

The Atlantic Bluefin is a voracious apex predator and a schooling species which ranges widely through the ocean, moving between seasonal feeding grounds and breeding locations.  Currently, scientists have distinguished at least three genetically distinct populations – western Atlantic, eastern Atlantic, and Mediterranean – with different spawning grounds.  However, these populations mix to some extent during the year, and animals have been known to cross the Atlantic in as little as 60 days.  They are managed as if there is a western Atlantic population and an eastern Atlantic and Mediterranean population, but that is almost certainly a simplification.  The western Atlantic population spawns at specific locations in the Gulf of Mexico in May and June, and used to range from Newfoundland to Brazil at other times of the year.  Bluefin tuna no longer occur in Brazilian waters, and overall, this population’s number of adults has declined to about 29% of numbers in 1970.  The eastern Atlantic and Mediterranean populations spawn at specific spawning locations within the Mediterranean from May to August.  At other times, the eastern Atlantic population ranges from Norway to the Canary Islands.  The size of the eastern Atlantic and Mediterranean populations together has declined to about 57% of numbers in 1970.  There are other differences between the western and eastern populations; members of the western Atlantic population do not mature until their 8th or 9th year, while those spawning in the Mediterranean begin between their 3rd and 5th year.  In both populations maximum age is 30 to 35 years although there are some early claims of 50 year old individuals.

People have fished for Atlantic Bluefin tuna for tens of thousands of years.  Phoenician fishermen operated traps for them in the Mediterranean around 2000 BC; they are mentioned by Aristotle and Pliny the Elder; and their bones have been retrieved from prehistoric archeological sites.  They are now perhaps the most valuable fish on earth because of the exceptional quality of their flesh for sashimi and sushi.  They were not always so highly valued.  Prior to the mid-1970s, Bluefin tuna were a low-value species because their highly flavored, red, blood-rich muscle was less suitable for canning than was the meat of other tuna species such as Albacore with its whiter meat.  (Albacore have one strip of red muscle along each side and this is typically removed in the canning process and diverted to cat food.)  But in the mid-1970s, Japan began to outfit its tuna fleet with ultra-cold freezers and fish could be held for the sushi market.  Suddenly, Bluefin from any ocean became highly valued and were being sold at auction at Tokyo’s Tsukiji Fish market for many thousands of dollars each.  Freezer-equipped fishing fleets began to target them explicitly.  In the mid-1980s, in Ceuta, Spain, large fish spent after spawning began to be collected by purse seine and placed into sea pens for fattening over several weeks or months before harvesting them for the sushi market.  This tuna farming evolved to include the capture and grow-out of younger Bluefin that were also shipped to Japan.  The value of this fish grew yet again, adding yet more pressure to overfish them.

Auction of tuna at Tokyo’s famed Tsukiji Fish Market

Fisheries for very valuable fish become exceedingly difficult to manage, because there is too much money to be made, temptation to flaunt the rules can be strong, and fish can be shipped rapidly half way around the world.  Fisheries for species that are taken on the high seas, rather than in national waters, are also difficult to manage because enforcement of rules is far more difficult.  Fisheries for what are called straddling stocks, meaning highly mobile species whose populations persist in moving across international borders, are also difficult to manage – and the Atlantic Bluefin travels throughout the Atlantic and the Mediterranean.  Its management since 1969 has been by ICCAT, the International Commission for the Conservation of Atlantic Tunas, an FAO-sanctioned body with representatives of 48 countries that border or engage in fishing in the Atlantic Ocean and its regional seas.  ICCAT has had to cope with deficiencies in data, excess fishing capacity, and the need to proceed by means of consensus as it worked to bring catches under control.  It should not be a surprise that Atlantic Bluefin have been overfished, despite sincere effort by numerous managers to prevent this happening.  Too many strikes against this beautiful fish.


Farmed vs Wild Fish and Difficulties in Management

“Increasingly, we will be faced with a choice: whether to keep the oceans for wild fish or farmed fish. Farming domesticated species in close proximity with wild fish will mean that domesticated fish always win. Nobody in the world of policy appears to be asking what is best for society, wild fish or farmed fish. And what sort of farmed fish, anyway? Were this question to be asked, and answered honestly, we might find that our interests lay in prioritizing wild fish and making their ecosystems more productive by leaving them alone enough of the time.”

― Charles Clover, The End of the Line: How Overfishing Is Changing the World and What We Eat


Tuna farming has exacerbated the management difficulties faced by ICCAT because fisheries management normally relies upon statistics gathered at or about the time of fish landings to assess the status of the population being fished.  When fish are ‘landed’ into a pen, reared for some time, and only then taken to market information on when and where they were caught tends to get replaced or simply forgotten.  When other fish are caught on the high seas, and shipped to distant ports instead of being landed nearby, more data tend to get distorted or forgotten.  When fisheries are managed by limiting catch, yet dependent on those doing the fishing to report their catches, under-reporting can become an easy way to catch more than you are entitled to.  ICCAT began attempts to reduce the catch of western Atlantic Bluefin in 1981, introducing firm quotas, and had some success given that at that time only three countries were fishing those waters.  Attempts to manage catch for the eastern Atlantic/Mediterranean fishery have been much more difficult, and reductions in allowable catch only commenced in 1996.  Despite the very high value of this fish, ICCAT scientists have continued to comment on the inadequacy of the data which they are using to make their recommendations on allowable catch, and on the extent of IUU (illegal, unreported and unmanaged) fishing.

The extent of the difficulty is shown in this graph from a recent study by Rashid Sumaila and colleagues using trade-based estimates of likely catch to determine probable extent of IUU fishing in the eastern Atlantic/Mediterranean fishery since 2005.   Their estimates of unreported catch (distance between the green (allowable catch) and the red (estimated actual catch) lines conform to ICCAT’s expectations, and have increased as the quota has been reduced so that, now, about twice as many fish are being taken as is permitted.  Late in 2012, WWF provided some insight into a portion of this illegal trade, documenting how some 18 thousand tonnes of live Atlantic Bluefin was shipped from various Mediterranean countries, via Panamanian-registry vessels, to Japan during the years 2003 to 2010.

Figure from Illegal Bluefin, a report from the Pew Environmental Group.

At present ICCAT and FAO both consider the west Atlantic stock to be ‘depleted’ – an FAO term meaning that the population has been depressed through over-fishing to the point that it is substantially less productive than it could otherwise be (this happened during the 1960s long before there were any limits on allowable catch).  The east Atlantic/Mediterranean stock is termed ‘overfished’, which means exactly what it says.  Current catches are too high to be allowed to persist if we want this fish to remain available into the future.  I think it is particularly worth remembering that this designation of ‘overfished’ is based on the reported catches, not on these plus the substantial IUU fishing that is taking place.

So, what else has been happening to Thunnus thynnus in recent years?  In March 2010, it was considered, but ultimately rejected, for inclusion on the CITES list of threatened species not permitted to be traded internationally.  Not surprisingly, Japan voted against, but so did 71 other of the 129 CITES member countries.  Canada joined Japan while the USA voted in favor of listing.  In 2011, IUCN placed it on the Red List as Endangered, but the Red List does not inhibit capture or trade.

‘Endangered’ means ‘in danger of extinction’.  If its status deteriorates further it can be moved to ‘Critically endangered’ and from there to ‘extinct in the wild’.  If nothing more, this gives an easy way to track its slow demise. 

Also in 2011, Boris Worm and Derek Tittensor of Dalhousie University published an article in Proceedings of the National Academy of Sciences examining a global trend in range reduction among large pelagic predators.  Their analysis for Atlantic Bluefin showed its distributional range had declined by about 46% since the 1960s, including most of its range off Brazil and in the South Atlantic.  This range contraction occurred at the same time as its overall abundance was falling about 70%.  In 2012, Rashid Sumaila and Ling Huang of UBC published in Marine Policy, an article on managing Bluefin in the Mediterranean.  They reproduced the following graph of declining ‘spawning stock biomass’ (a measure of population size) for the Mediterranean showing it had declined to just 40% of what it had been in the 1970s, which basically confirms what Boris Worm and everyone else knows to be true.  Numbers have been sliding for a long time, and continue to slide despite improving management and imposition of catch limits beginning in 1996.

Figure from Sumaila and Huang, 2012, based on ICCAT stock assessment of 2008.

In November 2010, meeting in Morocco under intense pressure from its members, ICCAT increased the overall allowable catch of Atlantic Bluefin for the first time in 10 years.  The limit for 2013 for the eastern Atlantic/Mediterranean stock will be 13,400 tonnes, up from 12,900 tonnes in 2012.  Its own stock assessment had suggested some modest improvement, and ICCAT did better than expected in holding the increase to just 500 tonnes.  The limit of 1,750 tonnes set for the western Atlantic stock in 2010 and 2011 was continued unchanged.  (Canada and fishing organizations argued for it to be increased; the USA argued for it to be lowered further – there is a pattern here.)  At its meeting, ICCAT also put in place some improvements for catch reporting, and took some minimal steps to stem IUU fishing – all good news, but probably not really good enough.  This iconic fish is hanging on by its finlets.

The Deepwater Horizon accident dumped oil and Corexit into the Gulf of Mexico during the 2010 spawning season, adding just one small additional problem for the western Atlantic Bluefin Tuna.  (Image courtesy U.S. Coast Guard Visual Information Gallery)

About here it seems fair to draw attention to the fact that the western Atlantic stock spawns in the Gulf of Mexico during May and June.  Nobody yet knows what happened to the spawning effort in 2010.  How do tuna larvae do, swimming around in oil and COREXIT?  We will know in six more years and it probably won’t be good news.

To end on a lighter (?) note, and to prove that in Canada the left hand really does not know what the right hand is doing….. while Canada was arguing for increased quotas at the ICCAT meetings in Morocco, COSIWIC (Committee on the Status of Endangered Wildlife in Canada) is proposing to list this species under our Species at Risk Act – a move that would stop the harvest within Canadian waters.  The time for public comment ended December 14th.  Predictably the media had quotes from P.E.I. fishermen who know better than the scientists, and the P.E.I. Fisheries Minister chimed in also.  But the scientific committee of COSIWIC has referenced the decline in spawning stock biomass, stating that numbers of breeding adult bluefin have plummeted 69 per cent since 1970 — from 265,000 to 66,000.


“I know the human being and fish can co-exist peacefully.”

― George W. Bush


So, how do I bundle this all together into a story with some hope in it?  ICCAT continues to improve its ability to manage this fishery, but probably not fast enough.  The more rare these beautiful fish become, the more valuable they become and the harder people will work to capture them.  Switching the sushi industry over to farm-bred (as opposed to farm-reared) fish would be technically very difficult, and the farmed fish will not taste like ones that have swam free, but then we got used to factory pork and factory chicken, and someday soon we will get used to cultured animal protein, the ultimate frankenfood.  I think the pressure on this fish is going to continue for some time to come.  Indeed, it is distinctly possible that despite all the attention, the Atlantic Bluefin is slated to become one of the next of the species we fish to extinction because we are too greedy, too selfish, and too willing to have just one or two slices of the best raw fish in the world.  Still, it remains possible that it will hang on, in greatly reduced numbers – numbers so low that it simply become uneconomic to send factory ships half-way round the world looking for it.  Then, rare as Bengal tigers, the Atlantic Bluefin could become that seldom-seen, but never forgotten, magnificent, wild fish; truly the tiger of the sea.  But if we do not learn before it is to late, and the Atlantic Bluefin does cease to exist, the oceans will be a lesser place, and we, too, will be smaller for needlessly causing its demise.