"To state that all exploited taxa will have collapsed by 2048, the authors have made a simple extrapolation of their results across the next 40 years. This is statistically dangerous," said Serge Michel Garcia, director of the FAO's Fishery Resources Division.

He added: "Such a massive collapse ... would require reckless behaviour of all industries and governments for four decades, and an incredible level of apathy of all world citizens to let this happen, without mentioning economic forces that would discourage this from happening."

The US-Canadian study warned that accelerating overfishing and pollution of the oceans could force seafood completely off of mankind's plates by the middle of the 21st century.

The scientists said they were "shocked" and "disturbed" by the conclusions of their own research, saying the trend toward mass disappearance of fish and seafood species was speeding up.

If not reversed, they said, humans would have to stop eating seafood by 2048.

"Most if not all conclusions regarding the relation between species diversity and the resilience of the ecosystem ... have been available for years if not decades," Garcia said in an e-mail to AFP.

"It is evident that a further decay of the situation of wild stocks can only be globally detrimental for food security," he said.

The effort to combat the situation, "as we see it from FAO, shows contradictory signs of progress (in a few leading countries) and stagnation (in many developed ones)," he wrote.

FAO member states are "struggling to implement" a 2001 code of conduct for responsible fishing, "often despite unfavouravble economic and social conditions", he said.

Positive signs include the implementation of the "ecosystem approach", which also dates from 2001 and is "progressing rapidly in a small number of leading countries", along with quotas and eco-labelling, he said.

In the Mediterranean Sea, trawling below a depth of 1,000 meters (3,300 feet) is prohibited, he added.

"Faster progress (would require) a stronger political will ... fuller collaboration of the industry, more participative governance and more deterrent enforcement," Garcia said.

Noting that the UN agency estimates global demand for fish at 180 million tonnes in 2030, Garcia said: "Assuming that wild stocks continue to produce about 90 million tonnes as they do today, this implies doubling the present aquaculture production with a not insignificant impact on the environment and a potential shortage in fish meal (used for aquaculture feed)."

Currently some 35 million tonnes of fish is processed into feed for farmed fish and livestock.

Nearly one fish in two, 43 percent, consumed in the world last year came from fish farms, compared with nine percent in 1980.

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