Are tuna stocks being overfished?

The industrial fishery for tuna began in the 1950’s, but in that short period, it has depleted stocks on a global scale, with total annual hauls rising from 550,000 to over 4 million tonnes in just fifty years.

Skipjack is by far the main tuna species caught, making up over half of the total tuna catch. Other significant species include yellowfin, bigeye, albacore and the two bluefin species. The main commercial tuna fishing nations are Japan, Taiwan and Spain.

The vast majority of these catches are destined for the canned tuna market, which is worth £250 million annually in the UK alone. The great bluefin tuna, on the other hand are destined for the prized Japanese sashimi market, where a single fish can be worth up to US$100,000. Increased demand for sushi and tuna steaks in the West have made tuna an important global commodity, making up around 10% of international fish trade.

Despite often amazing fecundity and massive, transoceanic ranges, most tuna stocks are now considered fully or overexploited. Their gregarious nature often means tuna schools are made up of different species which makes selectively targeting a single species difficult, as vulnerable and more abundant species shoal together.

According to assessments carried out by ICCAT, the organisation responsible for managing tuna fishing in the Atlantic Ocean, virtually all Atlantic tuna stocks are heavily exploited, some unsustainably so, and catches are, in many cases, in decline.

A large problem facing tuna on a global scale is the level of illegal, unreported and unregulated (IUU) fishing. As many tuna are caught on the high seas, it is hard to ensure all vessels adhere to regulations regarding the minimum size, total catch or fishing gear allowed by international management bodies. As a result a considerable number of the tuna caught in the open ocean are not reported to the authorities, which makes managing stocks and setting annual quotas an even harder job for scientists.



Bigeye - All stocks of bigeye tuna are overexploited and some are depleted. As bluefin stocks in the Pacific started to dwindle, large bigeye tuna were caught for the burgeoning sashimi market in Japan, with catches doubling from 1980 to 2000. Catches of bigeye peaked in 1994, but had plummeted by almost 50% by 2004. Catches have been fairly constant over the past ten years; not due to a sustainable fishery but rather the ever-increasing effort that goes into catching these fish. The large quantities of illegal catches for many years mean that scientific assessments of the abundance of the stock are very uncertain.

Yellowfin - Catches of yellowfin tuna have fallen over 30% since 2003. As with bigeye, larger individuals have been targeted for the sashimi market. Though the pole and line fishery is sustainable, the vast majority of yellowfin are caught on longlines and in purse-seine nets. Scientists are calling for a cut in the total allowable catch for this species, to allow stocks to recover.

Albacore - Albacore stocks in the Pacific are at record highs and the Marine Stewardship Council has given the U.S. and North Pacific pole and line fisheries its accreditation. Unfortunately, the same cannot be said for their Atlantic cousins, with an IUCN assessment labelling them ‘vulnerable to critically endangered’.

Skipjack - Skipjack are the most fecund of all the tuna and swarm in vast schools, up to fifty thousand strong. They constitute 60% of the total annual tuna catch with over two and a half million tonnes landed in 2007- a tenfold increase in fifty years. While Skipjack stocks are generally considered to be healthy, the characteristics of skipjack tuna stocks and fisheries make it extremely difficult to conduct stock assessments. ICCAT has not conducted a stock assessment for Atlantic (West or East) skipjack tuna since 1999, and there are no definitive conclusions available on the status of the stocks.

Bluefin - The majestic bluefin is the largest of all tuna, the biggest recorded individual weighing 679kg. They are warm blooded, their hearts pumping ten times faster than other fish of the same size and their powerful muscles can produce bursts of speed up to 100km per hour. It is these muscles that give their flesh the deep red colour so prized in Japanese sushi markets. The market for them is so lucrative that it has lead to the serial depletion of stocks; first in the Pacific, the Western Atlantic and more recently in the Mediterranean. They are listed as critically endangered by the IUCN and their management by the International Commission for the Conservation of Atlantic Tunas (ICCAT) was dubbed an ‘international disgrace’ last year in an independent review.

An almost unregulated farming industry in the Mediterranean, where wild individuals are caught and fattened in cages to increase their value, resulted in quotas being flouted and IUU fishing running rampant throughout European waters. Scientists have been calling for a massive reduction in the total allowable catch for many years but their cries have gone unheeded. The general consensus is that unless fishing ceases and the bluefin stocks are given sufficient time to recover, they will collapse in the near future. At a pivotal meeting in Marrakech in November 2008, ICCAT made headway in legislation preventing IUU fishing, but political agendas saw the total allowable catch remain at a level that may well result in the commercial extinction of Mediterranean bluefin - with some research suggesting that the current catch levels could remove all the adult fish in three years.



ICCAT also considers the populations of blue marlin, white marlin, and North Atlantic swordfish to be over-fished.

Tuna species are a significant source of food in many countries. They are very important economically, with world trade in tuna worth in excess of US$5 billion. In terms of the global trade in fish commodities, tuna accounts for around 8 per cent of imports by value and quantity.

Tuna is commonly consumed in two forms: either fresh, or canned:

Sashimi is prepared from fresh, high quality raw tuna meat, or from tuna frozen at temperatures below -40ºC immediately after capture. Traditional sashimi is prepared from the three species of bluefin, bigeye and yellowfin tunas. It is served in thin slices, dipped in soy sauce and/or wasabi (Japanese horse radish) and consumed raw. Sushi is a cylinder of rice combined with vinegar, with a slice of sashimi on the top or in the middle.

Tunas that are not acceptable for sashimi are sold in the steak market, generally in Europe and the United States. Steaks are generally prepared from bigeye, yellowfin and albacore tunas, mostly fresh but also frozen.

Japan is the world's largest producer and market for fresh and frozen tuna and tuna based products (excluding canned tuna), although tuna in the form of sashimi and steaks is becoming increasingly common within the European and North American markets.

The major importers of canned tuna are the United States, the United Kingdom and France, in terms of both quantity and value. Skipjack, yellowfin and albacore are the species principally used for canning. The fish, which are generally frozen, are cut up, cooked and then canned in brine or oil.

The depletion of worldwide tuna stocks is not just a disaster for the marine environment, but also for communities around the globe which have relied on these animals for millennia. The water surrounding the Pacific Islands supplies 6% of the world’s tuna and for some island chains, no tuna means no future. Industrial fleets have robbed locals of livelihoods and food, with many commercial vessels plundering more tuna in one trip than the artisanal fisheries can take in a year. However, this is not restricted to developing countries, and catches in many Mediterranean tuna traps fisheries have fallen to such low levels that a way of life five hundred year culture could disappear in the near future.