The following correction was printed in the Observer's For the record column, Sunday 3 May 2009.

Below Marine Protection Areas in South Africa and New Zealand were described as zones "where trawling is banned". It is only bottom trawling within 100m of the seabed that is banned. It is Benthic Protection Areas, not MPAs, that cover 30% of New Zealand's Exclusive Economic Zone.

A third of the world's oceans must be closed to fishing if depleted stocks are to recover, scientists and conservation groups have warned. Such a measure could "set the clock back 200 years" and reverse the decline in fish populations, after which responsible fisheries management could regenerate the industry.

Callum Roberts, Professor of Marine Conservation at the University of York, has reviewed 100 scientific papers identifying the scale of closure needed. "All are leaning in a similar direction," he says, "which is that 20 to 40% of the sea should be protected." Friends of the Earth, the Marine Conservation Society and the Royal Society for the Protection of Birds all support the idea of a 30% closure. "What we would see is a flourishing of life," Roberts says. "In 20 years, we could get to a point where a lot of species are in a far more productive state."

The proposal comes in the wake of a green paper calling for radical reform of the Common Fisheries Policy, which EU ministers admit has failed. It reveals that 88% of EU stocks are overfished (against a global average of 25%) while 30% are "outside safe biological limits" – meaning they cannot reproduce as normal because the parenting population is too depleted. In the North Sea, 93% of cod are fished before they have had a chance to breed.

The European Commission suggests a reduction in fleet size and a dramatic cut in fishing effort among its raft of measures, but Roberts believes these will not work without the creation of Marine Protected Areas (MPAs). "Just cutting fishing effort is not enough," he says. "If we are ever going to have sustainable fisheries, MPA networks are an essential, indispensable part of any rational management package."

In Iceland, Canada and the US, the creation of MPAs has "brought real increases in fish populations and real recovery of seabed habitats", Roberts says. "Populations of exploited species have increased five-, 10- or even 20-fold within five, 10 or 20 years."

The most convincing example is New England, where stocks of ground fish were "in a dreadful state" in the 1990s. Off Georges Bank, an area of nearly 20,000 square kilometres – a quarter of the fishing grounds – was closed to vessels, and fishing effort was reduced by "a draconian 50 per cent". In the past 10 years, Roberts says, there has been "a spectacular recovery" of key economic species.

As stocks within MPAs recover, the eggs and larvae of fish are carried on ocean currents to fishing grounds, Roberts explains. This helps replenish commercial fisheries. Fish also leave the protected areas, emigrating to places where they can be harvested legally.

Off Lundy Island in Devon, one of only three No-Take Zones (similar to MPAs) in British waters, the lobster population is eight times higher within the reserve. "We have already seen benefits in the lobster fishery immediately outside it," says Giles Bartlett, fisheries policy officer at the environmental charity WWF. In the Isle of Man, where a No-Take Zone for scallops has been created, "there have been significant increases in catches on the boundary of the reserve", he adds. "There, a limited size of reserve is supporting the whole fishery. If you scale those reserves up, you are going to see similar results for demersal [bottom-dwelling] fish stocks. We feel European seas would benefit from this kind of management."

The fishing industry is less convinced, saying pressure on stocks just outside a protected area can "mitigate against the impact" of the MPA. "It almost creates a bull's-eye for fishermen, who know the area on the periphery isn't protected," says Tom Rossiter, research and development manager at Seafish, the UK seafood industry body. "If you shut off an MPA, it will move the fishing effort somewhere else."

Phil MacMullen, head of environment at Seafish, says a distinction must be made between MPAs created to conserve habitats and biodiversity, and those created for fisheries management purposes. "If you are very lucky, you may find an area designated for conservation also gives you fisheries benefits," he says, but the likelihood is low. Seasonal closures at spawning times, and around specific areas such as nursery grounds, are already used effectively by fishermen.

Currently, there are 4,000 MPAs covering just 0.8% of the world's oceans. New Zealand has already closed 30 per cent of its Exclusive Economic Zone – offshore fishing grounds – to trawlers and Australia is considering a similar move. Under the Marine Bill, the UK Government has committed to designating a coherent network of new Marine Conservation Zones (MCZs) by 2012, though there is no mention of a percentage target.