By Paul Rincon
BBC News Online science staff
A team of UK scientists has come up with a cost for establishing a global network of marine "parks" to protect threatened ocean ecosystems.
The cost estimated in the report far exceeds current expenditure on marine parks Image: Callum Roberts
A network with 30% coverage of the oceans would cost $12bn (£6bn) to $14bn (£7.7bn) per year to run, they say.
Some experts say the costs are high, but the authors say the investment would safeguard - and increase - the global fish catch.
Details are published in Proceedings of the National Academy of Sciences.
"The expectation is that protecting areas from overfishing will lead to an improvement in fish catches over time," Professor Callum Roberts, a marine conservation biologist at the University of York, UK, told BBC News Online.
The 2002 World Summit on Sustainable Development in Johannesburg, South Africa, urged the creation of national networks of marine parks by 2012 to protect dwindling fish stocks.
This call was echoed at the 2003 World Parks Congress in Durban, South Africa, which recommended that at least 20-30% of every marine habitat should be protected from all fishing.
The team of researchers, from the universities of Cambridge, Cranfield, Wales and York, conducted a survey of the running costs of 83 marine protected areas (MPAs) worldwide, ranging in size from 100 sq m to 300,000 sq km.
Annual running costs per unit area were higher in small parks, those closer to coasts and in high-cost developed countries.
However, in the parks surveyed by the researchers, present income only accounted for half the amount needed to achieve ideal management standards.
The researchers took into account this shortfall when estimating the running costs. They came up with figures of between $5bn (£2.7bn) and $19bn (£10.4bn) per year to run, depending on what assumptions were made.
In addition to the figure for 30% coverage, the researchers also produced an estimated cost of $9.5bn (£5.2bn) to $10.4bn (£5.7bn) for 20% coverage.
Marine parks promote the recovery of fish stocks, say the researchers Image: Callum Roberts
Dr Christopher Delgado, senior research fellow at the International Food Policy Research Institute in Washington DC, US, regards the costs as very high.
"There is a widening recognition that there is a problem with overfishing. But the question is: 'Who's going to pay?' At the moment, nobody wants to be the one to pay," he told BBC News Online.
Lead author of the study, Andrew Balmford, of the University of Cambridge, is under no illusions about the large financial investment required and the difficulties of implementing such a complex programme at an international level.
"Meeting this commitment to marine protection will require international effort on an unprecedented scale," he says.
A global system of MPAs would create a projected one million jobs, the team argues. The models also assume no income from tourism, which contributes heavily to the funding of existing marine reserves.
Dr Delgado observes that, while it is relatively easy for countries to stop their citizens fishing, making sure those same people reap the benefits of government policies further down the line is more difficult.
Some argue that marine reserves in developing countries create new problems Image: Callum Roberts
But he adds that it is important to distinguish between the situation in developed and developing countries: "In developing countries there is less governance - the ability to control what's going on.
"As a result, marine reserves don't work too well, although they are frequently proposed. Even if they are enforced, all the people who used to fish there have nowhere to go."
Professor Roberts explained there was still a lack of understanding of what was involved in the successful management of marine reserves: "At the moment, there's been a great reluctance to protect areas from fishing.
"But fishing is one of the biggest impacts humans have on the sea. If we fail to curb that then we will fail in our efforts to restore the marine environment."