Sushi is in danger of falling victim to high oil prices after fishing industry groups warned that a third of the world's long-line tuna fleet - the ships that catch the high-grade tuna used in the Japanese dish - could remain docked this year as soaring fuel costs make fishing unprofitable.
The business is already in decline due to dwindling fish stocks. Japan Tuna, an industry group, said the cost of heavy fuel for long-range tuna ships had doubled over the past year to Y120,000 ($1,137, €733, £576) a kilolitre.
It said 20 per cent of Ja-pan's fleet of 360 ships might suspend operations during July to October, when catches tend to be lowest.
Wholesale prices for the choicest tuna cuts - those served in high-end restaurants - have risen by about 25 per cent in the past year, although the price of lesser grades sold in supermarkets has barely budged.
Japan had more than 800 long-range tuna ships a generation ago but the worsening economics of fishing and tighter international quotas have reduced that number by more than half.
Takeshi Hamada, professor at Tokyo Marine Science and Technology University, said declining stocks and higher fuel costs would hit consumers.
"Tuna sashimi used to be a dish for rich people. In the future it could become a delicacy again," he said.
Yuichiro Harada, managing director of the Organisation for the Promotion of Responsible Tuna Fisheries, a Tokyo-based group covering 12 countries, said 140 Taiwanese, Chinese and Korean ships had already decided to suspend operations during the season and more were likely to do so.
The organisation estimates that a third of the global long-line fleet - about 400 ships - could be out of action.
Mr Harada said many owners were only sending ships out to generate cash flow to pay off loans. Daily hauls have already fallen by about 20 per cent due to overfishing, while international quotas on the most valuable tuna varieties, such as southern bluefin, mean captains can no longer target them to maximise revenues.
"The quotas are bearable because we know that after a few years stocks will recover, but who knows when oil prices will come down again," he said.
Long-line tuna fishing uses hooks rather than nets to minimise damage to the fish and leave it suitable for serving raw. Japan is by far the largest market but demand is growing in North America, Europe and elsewhere in Asia - places that could see the sharpest price increases because of market constraints in Japan.
The threat of mass suspensions follows strikes and port blockades by French fishermen over high fuel costs and underlines the impact of rising oil prices on global food supplies.
The issue is one of the topics being debated at a United Nations-sponsored global "food summit" under way in Rome.
In Japan, experts say low-cost competition from Taiwan, South Korea and China, combined with consolidation among supermarkets - which has increased retailers' pricing power - have made it difficult for the country's fishermen to pass on higher costs.
