Marine protected areas (MPAs) would need to be tens of thousands of square miles in size � at least as big as the size of Wales � and would need to be established for decades to restore levels of cod and haddock, says the report.

Moreover, creating large MPAs would be likely to intensify fishing in the waters left open for business, so further measures to reduce activity would have to be brought in.

However, the report's authors, a team of marine ecologists from the University of Newcastle upon Tyne, suggest that these 'drastic' measures are unlikely to be feasible and would require a significant policy shift for them to be implemented.

They also acknowledge that there is an 'information deficit' regarding the costs and benefits of MPAs, particularly in the case of the North Sea, and call for more research.

Environmentalists and public bodies such as the Royal Commission on Environmental Pollution are lobbying the British Government to introduce MPAs in parts of the North Sea to conserve marine life and restore fish stocks. The Newcastle University researchers were asked by DEFRA to assess likely effects of MPAs in UK waters.

The report highlights that many MPA advocates are basing their opinions on scientific evidence garnered from small, conservation-oriented MPAs largely in tropical waters. Although the Newcastle team acknowledges that MPAs have brought many benefits to the tropics and elsewhere, it stresses this experience can not be applied to the North Sea, which possesses very different habitats and species.

The Newcastle University report suggests that small MPAs have conservation and localised fishery benefits in the UK, which is good news for shellfish and finfish (e.g. scallops and lobsters) but the MPAs will have to be very large to achieve recovery of North Sea cod stocks.

For the report, Professor Nicholas Polunin and Dr Chris Sweeting, of Newcastle University's School of Marine Science and Technology, reviewed a range of scientific evidence. This included information from existing MPAs in the North Atlantic Ocean, such as those at Lundy Island in the Bristol Channel, the Isle of Man, Georges Bank in the USA and Bonavista Bay in Newfoundland, Canada.

Prof. Polunin said: "Evidence suggests closing off small areas of the ocean won't deliver results with regard to highly mobile species like cod and haddock. These fish, which are among the most economically sought-after species, may travel hundreds of miles to move between spawning and feeding areas.

"You therefore need to create bigger protected areas and enforce them for several decades if you are to see a significant, lasting effect on stocks, which are massively depleted to historically low levels. However, this would raise the problem of intensive fishing activity in areas that are left open, and further fishing restrictions would have to be brought in to address this."

But Prof Polunin added that a lack of information made it difficult to provide accurate predictions: "Although MPAs are valuable tools for the preservation and enhancement of the marine environment, many of the costs and benefits remain speculative due to a lack of research in what is a comparatively new tool for fisheries management. There is a critical need to remedy this information deficit."

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