Scientists studying global catches of fish between the years 1988 and 1991 have shown that current levels of fishing are fundamentally unsustainable because of the fragility of the marine ecosystem.
They found that up to a third of the total quantity of fish living in the most productive parts of the ocean are taken to maintain current levels of consumption. This is basically unsustainable, they say.
Because the fishing industry takes fish from all levels in the ecosystem - from shrimps to tuna - its huge appetite threatens to destroy the delicate balance of marine life.
The scientists' research is based on estimates of the quantity of the Sun's energy captured by marine plankton - needed by the marine environment to sustain fish stocks.
They calculate that 8 per cent of the total marine plankton (algae) is required to maintain fish stocks throughout the world, about four times previous estimates. But in shallow seas that are rich in fish, such as continental shelves, this jumps to between 24 per cent and 35 per cent of the total amount of marine plants.
"This is a really staggering figure,'' John Beddington, professor of population biology at Imperial College, London, said. ``The implication is that current catch levels are probably not sustainable.''
Professor Beddington says that the new research, by Daniel Pauly and Villi Christensen at the International Centre for Living Aquatic Resources Management in Manila, the Philippines, is important because it demonstrates the global fragility of the fishing stocks. ``We know individual stocks have collapsed but here we're talking about the whole world,'' Professor Beddington said.
Dr Pauly's research is based on figures from the Food and Agriculture Organisation of the United Nations which show that of the total world fish catch of about 94 million tons a year, some 27 million tons are discarded for economic reasons, essentially because the fish are too small or of the wrong type.
The research shows that human activity is having a far greater impact on marine life than has been realised, Dr Pauly said. ``At the end of the day everything relies on the marine algae and we have turned the seas into a production system for fishing.''
Professor Beddington said the research emphasises the need to change global fishing policy. He said the fishing industry is overcapitalised and losing $54bn (£33bn) a year. ``These losses are largely met by subsidies. The failure of fisheries management to address the problems of unrestricted access and to stop unsustainable levels of harvesting - which has led to the depletion of many major stocks - is estimated to be costing a further $25bn each year.''
The basic problem, Professor Beddington said, is that there are ``too many fishing boats'' in the world.
Even if overfishing is stopped, he warned, there is little likelihood that fishing stocks will recover to exactly what they were before.