Michael McCarthy: Exploitation of global stocks has hit a dangerous peak

However you look at it, there are only so many fish in the sea, and the number that can be caught all around the world now seems to have reached its limit.

The total global catch has climbed steadily for more than half a century after the Second World War from about 20 million tons to about four times that figure. But in recent years it has reached a peak, despite continuing fishing effort from nearly 25,000 big fishing boats.

The implication is clear - world stocks as a whole are now being globally overexploited, and declining. The latest figures available, from the one organisation that keeps them, the UN's Food and Agriculture Organisation (FAO), show that the total of wild fish caught in the sea went from 75 million tons in 1999 to 76.8 million tons in the year 2000. But it fell back to 74.9 million tons in 2001 and 72.5 million tons in 2003.

The figures have to be read carefully, because the full world fisheries totals include fish from farming, which is rapidly expanding right across Asia, and inland fisheries. Another problem with the statistics is that the Chinese, the world's biggest harvesters of sea fish, have for years been massively inflating their catch figures, a team of fisheries researchers from the University of British Columbia at Vancouver declared in 2001. In a paper in the journalNature, Reg Watson and Daniel Pauly alleged that a clearly declining trend in world catches had been masked by the Chinese practice of increasingly over-reporting the amount of fish China lands each year. Fisheries scientists think regional officials exaggerate catches so that they can meet constantly increasing targets.

Using statistics gathered by the FAO since 1950, the scientists created maps of world fisheries catches and then built a computer model to predict catch sizes in different ocean regions.

It showed China's reported catches were unrealistically high when compared with catches from other ocean areas that have similar characteristics. The difficulty was that the FAO said it had to accept the figures national governments gave.

The FAO says China remains the world's largest fish producer, with reported fisheries production of 44.3 million tons in 2002, providing an estimated domestic food supply of 27.7kg per capita, as well as production for export and non-food purposes. However, it now acknowledges "there are continued indications that capture fisheries and aquaculture production statistics for China may be too high".

The vast majority of the world fishing fleet is concentrated in Asia. Peru takes the second biggest catch after China - nearly 9 million tons annually - followed by the US, Indonesia, Japan and Chile. The most-caught marine species is the Peruvian anchovy, followed by Alaska pollock and skipjack tuna.