China’s high-seas fishing fleet, the largest and farthest ranging in the world, is only economically viable due to state subsidies, while Japan and Spain provide even larger funding to their long-distance fleets than Beijing, according to a study.

Governments provided subsidies for fishing in the high seas — areas outside national waters that cover about two-thirds of the world’s oceans — worth $4.2bn in 2014, far exceeding profits derived from the activity, said the authors of a report published this week in the journal Science Advances.

Environmental groups such as Greenpeace have called for a ban on high-seas fishing due to declines in stocks of fish such as tuna and shark. Some 4.4m tonnes of high-seas fish worth $7.6bn were caught in 2014.