Jellyfish, slime and the International Conspiracy to Catch All Tuna  

The Observer has one of those sorry tales about over-fishing that appear in the press from time to time - How the world's oceans are running out of fish.

The future of our seas has never been more precarious. Ninety years of industrial-scale overfishing has brought us to the brink of an ecological catastrophe and deprived millions of their livelihoods.

It is early morning in Barcelona's La Boqueria market and the fish stallholders are setting out their wares. Mounds of pink and grey glisten down the dim alleys - shoppers and tourists peering at the fins and tentacles. It is not like any fish shop in Britain - some stalls sell five different species of squid and cuttlefish, half a dozen types of shrimp and prawn, 10 different cuts of salt cod. It is a fish eater's haven in the heart of a city that eats and sells more fish than anywhere else in Europe.

Anyone who cares about where their fish come from - and this should mean anyone who wants to go on eating them - should take two tools when they visit the fishmonger. One is the handy guidance provided by the Marine Conservation Society, Fish to Avoid and Fish to Eat (the latter is still the longer); the other is a ruler. My ruler is the type handed out to commercial fishermen by the international advisory body, Incofish, and has pictures of key species with marks indicating when they can be considered mature (and, thus, OK to catch).

So I set about lining up my ruler against the La Boqueria fish, starting with the mackerel (should be 34cm), the plaice (39cm) and the redfish (45cm). All turn out to be mere babies. The mackerel is half the designated length. A glance around the stalls shows 10 or more species on the MCS's Avoid list, including hake, swordfish, monkfish, bluefin tuna and, of course, cod.

I don't spend much time doing this because the Catalan fishmongers don't like my ruler - or me. They don't want to talk about why they are selling tiny hake (one of Europe's most endangered species) and why not a single fish in the market has any 'sustainable' labelling.

One old lady asks me what I'm after. 'I want to know why the Spanish are eating so many undersized fish from populations that are running out,' I say. 'It's simple,' she says. 'We like fish and small fish taste better.'

Is anyone not aware that wild fish are in deep trouble? That three-quarters of commercially caught species are over-exploited or exploited to their maximum? Do they not know that industrial fishing is so inefficient that a third of the catch, some 32 million tonnes a year, is thrown away? For every ocean prawn you eat, fish weighing 10-20 times as much have been thrown overboard. These figures all come from the United Nations Food and Agriculture Organisation (FAO), which also claims that, of all the world's natural resources, fish are being depleted the fastest. With even the most abundant commercial species, we eat smaller and smaller fish every year - we eat the babies before they can breed.

Callum Roberts, professor of marine conservation at York University, predicts that by 2050 we will only be able to meet the fish protein needs of half the world population: all that will be left for the unlucky half may be, as he puts it, 'jellyfish and slime'. Ninety years of industrial-scale exploitation of fish has, he and most scientists agree, led to 'ecological meltdown'. Whole biological food chains have been destroyed.

Many of those fish you can see in such glorious abundance in Spanish markets - and on our own supermarket shelves - come not from European seas but from the coasts of the continents of the poor: Africa, South America and parts of Asia. Fishermen have always roamed far afield - the Basques began fishing the great cod populations off Newfoundland at least 500 years ago. And when serious shortages in traditional stocks around Europe began to be commercially apparent 30 years ago, the trawler fleets began to move south.

Strangely one of the first international attempts to conserve fish stocks, especially for the more easily exploited nations, also became part of the disaster. The United Nations Convention on Law of the Sea, signed in 1979, extended national rights over fisheries to 200 miles from a country's coasts. But it included a provision that, if fish stocks in that zone were surplus to national needs, the country could sell its rights to outsiders. That convention allowed cash-strapped and sometimes corrupt countries in west Africa to raise funds by letting the industrial trawler fleets in. Since 1979 the EU has negotiated deals on fishing rights with a string of impoverished African countries. Despite the EU's own studies indicating massive and quite possibly irreversible damage to fish stocks off west Africa, these deals continue to be struck.

In 2002, the year an EU report revealed that the Senegalese fish biomass had declined 75 per cent in 15 years, Brussels bought rights for four years' fishing of tuna and bottom-dwelling fish on the Senegal coasts, for just $4m a year. In 2006, access for 43 giant EU factory fishing vessels to Mauritania's long coastline was bought for £24.3m a year. It's estimated that these deals have put 400,000 west African fishermen out of work; some of them now take to the sea only as ferrymen for desperate would-be migrants to the Canary Islands and Europe. And among the millions of Africans who depend on fish as their main source of protein, consumption has declined from 9kg per year to 7kg.

North Atlantic fish stocks have been in decline for well over a century. Callum Roberts points out in his recent book The Unnatural History of the Sea that it was obvious from the 1880s that fish stocks were in decline. Fish catch records from the 1920s onwards show that, despite the enormous improvements in boat design and trawling technology and better refrigeration, catches of the great Atlantic species, such as haddock, cod, hake and turbot, remained constant or slowly declined. As they have ever since.

Unlike global warming, the science of fish stock collapse is old and its practitioners have been pretty much in agreement since the 1950s. Yet Roberts can think of only one international agreement that has actually worked and preserved stocks of an exploited marine animal - a deal in the Arctic in 1911 to regulate the hunting of fur seals on the Pribilof Islands. So why has the international community failed so badly in its attempts to stop the long-heralded disaster with our fish?

'Quite simply,' Roberts says, 'agreements and deals brokered by politicians will never be satisfactory. They always look for the short-term fix.' ...

The Newfoundland cod fishery, for 500 years the world's greatest, was exhausted and closed in 1992, and there's still no evidence of any return of the fish. Once stocks dip below a certain critical level, the scientists believe, they can never recover because the entire eco-system has changed. The question is whether, after 50 years of vacillation and denial, there's any prospect of the politicians acting decisively now. 'It is awful and we are on the road to disaster,' says Tudela. 'But the collapse - in some, not all the situations - is still reversible. And it's worth trying.'