While the powerful new film The End of the Line has sparked a media frenzy of outrage, and pricked the conscience of many people about eating endangered fish, especially tuna, it's not like any of this information is new. The data are unequivocal and have been for years.
The bluefin is a magnificent, iconic creature whose days are now numbered. Since industrial-scale fishing of southern bluefin tuna began in the 1950s, for example, stocks have been reduced by some 95 per cent and the species was listed as endangered by the International Union for the Conservation of Nature (IUCN) in 1996.
According to the World Wildlife Fund, the bluefin will be extinct in just 3 years and yet the response of top-end restaurants, such as the Anglo-American Japanese chain Nobu, is to blather on about the ‘cultural significance' of eating tuna for the Japanese people - and likely hike up the price of their tuna dishes as stocks become more difficult to obtain.
Sadly the global, and in particular the Japanese, appetite for bluefin shows no sign of slowing. But of course, most of us don't make a habit of dining in expensive restaurants like this or of eating bluefin. When we eat tuna we usually eat it from the tin and it is likely to be the yellowfin, skipjack, albacore or sockeye variety. Tuna producers would have you believe that these types of tuna are the ‘rats of the sea' (though I dare any of them to use this as an advertising slogan) - meaning they are plentiful and not at risk. But don't pat yourself on the back just yet.
Today, around 5 per cent of the world's entire fish catch, by weight, is tuna and the global tuna business is worth around $5.5bn. The fish are caught in the Pacific, Atlantic and Indian oceans and there are processing and canning centres across the world, in places such as the Maldives and the Philippines.
All of the 23 identified, commercially exploited stocks are heavily fished; at least nine of these are classified as fully fished and a further four classified as overexploited or depleted. Three stocks are classified as ‘critically endangered', three as ‘endangered', and three as ‘vulnerable to extinction'.
Studies show, for instance, that the yellowfin, the UK's favourite tinned tuna, is likely just 15 years away from extinction due to chronic overfishing. Likewise Pacific albacore seems plentiful for the moment, but Atlantic stocks are considered ‘vulnerable' to ‘critically endangered'. According to a recent Greenpeace report, skipjack is the highest volume tuna catch in the world, yet the huge overcapacity in purse-seining fleets - the most common method of catching skipjack (see box below), is now undermining both the sustainability of the stocks and the economic viability of the industry itself.
The increasing use of Fish Aggregation Devices (FADS), (floating devices around which tuna and other large fish instinctively aggregate in vast numbers), as a means of rounding up fish for the purse seiners, means that the skipjack fisheries also threaten the survival of the more vulnerable bigeye and yellowfin since large amounts of juveniles of these species are caught as bycatch.
In 2001, a study of the by-catch of the purse-seine tuna fishing industry in the western Indian ocean for example, found that between 1990 and 1995 the boats caught 118,000-277,000 tons of yellowfin and skipjack tuna. The by-catch - which went largely unrecorded by the fisheries - was staggering: 944-2270 tons of shark; 720-1877 tons of rainbow runners; 705-1836 tons of dolphin fishes, 507-1322 tons of triggerfish; 113-294 tons of wahoo; 104-251 tons of billfish; 53-112 tons of mobula and manta; 35-89 tons of mackerel scad; 9-24 tons of barracudas, and 67-174 tons of other fish. In addition there were unspecified numbers of turtles, whales and dolphins caught in the nets. Other studies suggest that endangered dugong are also caught in the nets. By-catch is considered waste and all these fish and marine mammals were thrown back into the ocean dead. A high price to pay for the tuna in your sandwich or casserole.
Toxins in the Tin
Sustainability is not the only concern with tinned tuna. Like all top marine predators tuna can over time bio-accumulate toxins that have been dumped into our seas - such as mercury.
Mercury is released from the smokestacks of coal-fired power plants, cement kilns and certain mining activities. Once in the air, it rains down into waterbodies where it finds its way into fish, accumulating especially in fish that are higher up the food chain.
In 2005, US pressure group the Mercury Policy Project tested a sample of white albacore tuna and found levels of the heavy metal were significantly higher than in other tuna species and that 5 per cent of tins analysed were so contaminated they should have been recalled as unfit for human consumption.
More recent data from the US Geologic Survey (USGS) suggests that the rate of mercury contamination in tuna and other Pacific fish has increased 30 percent since 1990.
Roughly 75 percent of all human exposure to mercury comes from eating fish. Mercury is a central nervous system toxin and exposure early in life, even in very small amounts, can lead to permanent developmental effects including reduced attention span, language, visual-spatial skills, memory and coordination. In adults it can result in paraesthesia (a tingling sensation on your skin), depression, arrhythmias and cardiomyopathies, tremors, insomnia, personality changes and irritability, headaches and blurred vision amongst other symptoms.
Laboratory tests in the US in 2007 found that even canned light tuna, which is touted as a ‘safer', lower mercury seafood choice, can be unsafe. Six percent of cans tested contained more than 0.35 ppm, and as much as 0.85 ppm. White or albacore canned tuna had an average of 0.35 ppm. The designated ‘safe' level is 1.0 ppm.
It’s easy to be sceptical about the potential effect of something so ubiquitous as tinned tuna on our body burden of mercury. But when Canadian researcher Bruce Lourie tried to gauge the damage done for his new book Slow Death By Rubber Duck, he found that eating 7 tuna meals over a two day period (tinned, sushi, sashimi, and grilled tuna steaks) Increased blood mercury levels by nearly 2.5 times.
Down on the farm
So is farmed tuna the answer? For a big species that needs to move constantly and needs hundreds (maybe thousands) of miles of ocean territory in which to roam in order to be healthy the answer is no. Tuna farming has all the attendant problems of other fish farms such as those for salmon including disease and the difficulty of getting the unhappy fish to breed in captivity - usually requiring them to be dosed up with hormones. Sadly, the fish-farming of today has more in common with the factory farms for meat, eggs and dairy: generating large amounts of waste and entirely removed from ecological systems (see Ecologist article 'Fishy Business'). And farming, which occurs in pens at sea is no guarantee of toxin-free tuna.
The provenance of tuna can be difficult to establish. Most tins don't tell you how or even where the fish were caught. In 2008 a report by Greenpeace ranked retailers and canning companies in order of their tuna-fishing policies. Sainsbury, Co-op and Marks & Spencer came top; Princes and John West - most of whose fish came from purse-seiners - came bottom.
Even so, conservationists say pole and line caught tuna or that sourced through trolling (see box below) practiced by small scale domestic sustainable fisheries is a cleaner method since there is no by-catch. (There is even some evidence that albacore caught with long-line fishing gear are older fish and have accumulated more mercury than younger, pole and line, or troll-caught albacore - another reason to only buy sustainably caught tuna).
In the last few years the Marine Stewardship Council has begun to certify small-scale sustainable tuna fisheries. Although there are some brands of tinned tuna that are troll and/or pole and line caught - in the UK the Co-op and Sainsbury's have already moved their sourcing towards pole and line fisheries for tinned tuna - fish caught in this way are more likely to be sold in local markets rather than processed and shipped worldwide.
Plenty more fish in the sea?
There's no happy answer to the problem of tinned tuna. If retailers want to continue selling tuna in the future, then they need to stop buying from unsustainable, unfair and, in some cases according to Greenpeace, illegal sources. To be able to ensure that the tuna on their shelves is sustainably caught from well managed fisheries, retailers must be able to trace the whole suplly chain accurately. This means knowing where, when and how it was caught, and also that the fishing operator pays a fair price for their fishing license from the coastal states whose resources they exploit.
If, as a consumer, you care about fish stocks and the future health of our ocean ecosystems, and your favourite brand or retailer cannot guarantee where your tuna comes from or how it was caught, then you will simply stop buying it (sustainable, locally caught mackerel is a good substitute in your lunchtime sandwich). Retailers and fisheries will soon get the message.
KNOW HOW YOUR TUNA WAS CAUGHT
The vast majority of fished tuna is caught by large commercial fishing vessels using one of two methods: long-line fishing and purse seining. Both methods produce by-catch in large numbers. Other methods have significantly smaller environmental impact but are responsible for only a tiny fraction of the fish available to consumers in the United States and Europe.
This method involves releasing extremely long fishing lines - some of them long enough to stretch from London to Brighton - to which are attached shorter lines and thousands of baited hooks. It's effective but not selective and can end up catching other species, such as the seabirds that go after the bait in shallow waters. The birds, snared by the hooks, usually drown.
Longlines, which are made of non-biodegradable monofilaments, are often lost and can drift at sea indefinitely, snagging, entangling, and killing marine life for decades after they ceased ot be used by fishing vessels.
This method is particularly effective at catching yellowfin tuna. It involves laying out a very large net in a wide circle, which is then drawn inward, capturing the marine life inside. It also produces a significant by-catch of other fish, turtles and marine mammals.
Pole and line/trolling
Pole and line fishing, or bait-boat fishing, is the oldest fishing method. Used by local fishermen and sport fishers, it causes far less harm to the environment than commercial methods do. Trolling is a fishing method in which multiple (5 to 21) single lured or baited lines are towed behind a slowly moving vessel. Both methods are very selective and eliminate the problem of by-catch.