Tuna catches across the Indian Ocean have fallen sharply in the last two years but experts are split over what is threatening the region's €3.8 billion industry.

Conservationists blame years of unchecked exploitation while processors say climatic conditions may be driving the fish deeper away from their nets.

Tuna catches in the Indian Ocean, which accounts for roughly a quarter of the global haul, dropped by about a third last year to their lowest level for more than a decade.

Early indicators for this year show catches to be markedly below recent averages, Alejandro Anganuzzi, head of the Indian Ocean Tuna Commission, told Reuters.

"We cannot rule out the possibility that overfishing has occurred," he said.

Other forces such as changes in wind patterns, currents or the impact of predators might also play a part, he said.

Similar falls in catches are seen in the Pacific, where environmental groups say decades of overfishing has slashed some stocks by as much as 85 per cent. European fishing firms now chase tuna in the Pacific after numbers fell in the Atlantic.

Last month, EU fisheries regulators banned trawling for bluefin tuna in the eastern Atlantic and Mediterranean to stop overfishing of a species that was approaching complete collapse.

Rewards for fishermen remain high.

Market prices for the delicacy have roughly tripled since last year. In Japan, where there is huge demand for tuna to make sushi, top quality fish can sell for up to €64,000 each.

In the Seychelles, tuna canning is worth €116 million a year and accounts for more than 90 per cent of export earnings.

One of the biggest canners in the region, Indian Ocean Tuna (IOT) Ltd, says its volumes have dwindled by about 18 per cent to 70,000 tonnes processed annually for the last two years.

IOT's general manager, Alain Olivieri, said the Indian Ocean had seen a "terrible" fall in catches, which he blamed on higher water temperatures pushing fish deeper out of reach of nets.

Experts are divided over whether these warmer warmers are the result of climate change or of cyclical ocean conditions.