EXTINCTION comes in various ways. The dodo was done in by sailors who not only killed the birds themselves but also brought to Mauritius animals such as dogs and pigs that plundered their nests. Przewalski's horse, which once roamed the steppes of Mongolia, is thought to have become too dispersed in the wild to breed. It was saved from extinction only because there happened to be some specimens in European zoos that were reintroduced to Mongolia in the 1980s. As efforts to prevent the bluefin tuna suffering a similar fate are increased, some conservationists wonder whether there will still be a breeding population left to save.

Bluefin tuna are a pelagic species: they live in the open waters, far beyond the reach (and governance) of individual nations. They are also one of those predators at the top of the ocean's food chain, preyed upon mostly by man. They grow up to four metres (12 feet) in length, weigh as much as 250kg (550lb) and, when chasing prey—mostly sardines—can swim at a speed of 70kph (45mph). They also range widely, traversing the Atlantic Ocean to reach breeding grounds in the Mediterranean Sea. But what was once known as the common tunny has, over the past few decades, come to be at serious risk of extinction, thanks to overfishing driven by demand from Japan, where bluefin tuna are considered a delicacy and are used in sushi and sashimi.

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Efforts to protect the species have floundered. Now conservationists are trying a new approach, using the Convention on International Trade in Endangered Species of Wild Fauna and Flora, better known by its acronym, CITES. The convention strictly controls, for example, trade in ivory, in order to protect elephants from poaching. It has the power to ban any international trade in a species deemed endangered. But because the convention is an intergovernmental treaty, a member state must propose a species for this status. On June 5th Monaco did this for bluefin tuna.

On July 16th Nicolas Sarkozy, the French president, announced that France would support the placing of Atlantic and Mediterranean bluefin tuna on the CITES list. He was joined by Huw Irranca-Davies, Britain's fisheries minister, who said he would seek American support for the proposal. As America already thinks the Atlantic bluefin tuna is overfished by Europeans, Mr Irranca-Davies will probably be pushing on an open door. The proposal therefore looks likely to succeed, though that will not be known for certain until the countries that have signed CITES meet to discuss the proposal in March 2010.

Yet even if the trade in bluefin tuna were to be halted completely, there would be no guarantee that the species would recover. Experience with other fisheries, such as the collapse of the cod population of the Grand Banks off Newfoundland in 1992, has shown that the dynamics of an ecosystem can change when a top predator is removed completely. Fifteen years later, the northern cod stock has not recovered.

In a study published last year in Conservation Letters, a group of scientists led by Brian MacKenzie, of the Technical University of Denmark, describe how they ran a computer model of the bluefin tuna's population dynamics. Their conclusion is that, on current trends, the population in the north-east Atlantic and Mediterranean will collapse because young fish are being caught before they have the chance to breed. Indeed, the World Wildlife Fund, a nature conservation organisation, reckons that bluefin spawners will be virtually eliminated by 2012.

As Prince Albert, Monaco's ruler, wrote in the Wall Street Journal last month, “The forces of selfishness and stupidity that wiped out the great whales and the northern cod in the last century are steaming ahead at full speed... The bluefin tuna is as endangered as the giant panda and the white rhino.” Unless a ban is enforced almost immediately, the only examples of the species could be found in large aquariums.