James Joseph, New Scientist 29 Jul 09;
IS IT OK to eat tuna without feeling guilty? The media is full of reports claiming the demise of tuna stocks. Monaco, France and the UK are calling for the trade in bluefin tuna to be banned. There is no doubt that some tuna stocks are heavily overfished, but they are not the source of the fish you eat in a tuna sandwich or salad. In fact, it's OK to continue eating tuna - at least for now.
Tuna are widely but sparsely distributed throughout the world's oceans. They grow rapidly to very large size and can support major fisheries. They also migrate long distances, and their travels carry them through the fishing zones of many nations and also international waters.
This wanderlust makes tuna more complicated to manage than less nomadic fish. Because the level of fishing in one area can affect their abundance in others, cooperation among the nations through whose waters tuna migrate and those whose fleets catch them is essential. Accordingly, tuna stocks are managed by five regional fisheries management organisations, whose duties are to conduct scientific studies and implement conservation measures to ensure the tuna harvest is sustainable.
Taken together, tuna account for about 5 per cent, or 4.2 million tonnes, of the world's annual harvest of marine fish. The catch is made up of seven principal species. Skipjack, used mostly for canning, accounts for 59.1 per cent. Yellowfin is next with 24.0 per cent, bigeye 10.0 per cent, albacore 5.4 per cent, and the three species of bluefin (southern, northern [Atlantic] and Pacific) make up the remaining 1.5 per cent. Bluefin are the giants of the tuna family and the most highly prized.
These seven species are divided into 23 stocks. Scientific studies have shown that, of these, six are overfished, six are fully utilised (which means they can't sustain any increase in the catch), and nine are not yet fully utilised. Two have not been adequately assessed.
The three most seriously overfished stocks are eastern Atlantic and Mediterranean bluefin, western Atlantic bluefin, and southern bluefin. Unless measures are implemented to reduce catches they might not recover. For the fourth bluefin stock, in the Pacific, a full assessment is currently underway.
Of the remaining three overfished stocks, North Atlantic albacore is recovering and is nearly back to its optimum level; the eastern Pacific bigeye stock is slightly overfished, but management measures due to be implemented this year may allow it to rebuild; and yellowfin in the Indian Ocean may recover thanks to recent pirate activity, which has led many vessels to leave the area.
The other tuna stocks are reasonably healthy. Three of the six fully utilised stocks are at risk of becoming overfished, but conservation measures are being put in place. Overall, about 90 per cent of tuna catches come from stocks that are not overfished.
So contrary to what you might have been led to believe, tuna stocks are largely in good shape. The challenge is to ensure that the healthy stocks stay healthy and the overfished stocks recover.
There are many obstacles to overcome. Each of the management organisations comprises between 6 and 48 member states; most of them require consensus of all the members in order to enact conservation measures, and this is difficult to achieve.
One of the main problems is that there are too many tuna boats - capacity is 10 to 40 per cent more than is needed to harvest the stocks at sustainable levels. There are no strict controls to stop new vessels entering most tuna fisheries, so they continue to be built. This overcapacity results in excessive competition for limited supplies and diminishing economic returns, and makes it difficult for nations to agree conservation measures.
This sort of short-sighted race to exploit a resource without regard for the long-term consequences is what has led to overfishing in many of the world's fisheries. It stems from the tradition of open access to high-seas fisheries, a concept enshrined in the United Nations Convention on the Law of the Sea.
It is time to change the convention and introduce new management systems. The first step would be to limit entry into the fishery. Next, assigning fishing quotas to individual boats, rather than allowing them to compete for as large a share of an overall quota as possible, would motivate fishers themselves to support conservation measures in order to protect their share.
However, achieving consensus for such systems will be difficult because of tension between the haves and have-nots. Most of the have-nots are developing states that aspire to establish tuna-fishing fleets. Tuna pass through waters under their control and many are members of regional management organisations, but in many cases they lack the capital and infrastructure to run fleets. Because they want a piece of the action, they are unlikely to agree to limits on new vessels unless they are guaranteed a right to acquire vessels.
Excluding bluefin, tuna fisheries are close to peak productivity. Unless effective conservation measures are implemented, they will slide down the slippery slope of overfishing. The situation is serious enough that scientists and environmental organisations have joined together with the major canned tuna processors to form the International Seafood Sustainability Foundation. Its purpose is to support the five fisheries management organisations in their duties to implement science-based conservation.
The time for states to negotiate meaningful conservation measures is now, before the healthy stocks become overfished and the overfished stocks are further depleted.
James Joseph serves on the International Seafood Sustainability Foundation's board of directors and is chair of its science advisory committee
