It has been invisible, so it has gone largely unheeded, but the wrecking of the seas is now the world's gravest environmental problem after climate change, British scientists said yesterday.

Such destruction has been caused by over-fishing in the marine environment and only massive protected zones, where all fishing is banned, will allow the sea's damaged areas to recover, members of the Royal Commission on Environmental Pollution said.

These non-fishing reserves should cover fully 30 per cent of UK territorial waters, the commission suggested, in the most drastic call ever made to scale back fishing in Britain or Europe. The proposals were welcomed by environmentalists, but attacked by some fishing industry groups, who said they would threaten yet more livelihoods, and that recovery measures have already been taken.

But the commission, representing some of the country's most senior environmental scientists, was insistent. It is not just the question of plunging fish stocks, critical though many of these are, it said in a new report; rather, the concern is for the whole marine ecosystem, with seabirds, dolphins and porpoises killed in their thousands, smaller marine organisms wiped out and the seabed comprehensively destroyed by trawling over vast distances.

The report, Turning The Tide, calls on people and policymakers everywhere to recognise for the first time the real scale and true nature of the problem: that decades of competitive fishing have put the whole marine ecosystem under siege. The central point is that it is the ecosystem, and not just threatened individual fish stocks, such as cod or haddock, that needs looking after.

The commission's members call for a simple but profound policy change: the "presumption in favour of fishing" should be reversed. Until now, fishing has been allowed anywhere unless the regulating authorities can demonstrate that harm is being done to ecosystems or habitats.

But this has not prevented severe ecosystem damage, the commission reports, saying that it should be for fishing interests to demonstrate that their activities will not cause harm. There should be spatial planning in the sea just as there is on land, it says.

Sir Tom Blundell, the commission's chairman and a professor of chemistry at Cambridge University, said: "It is hard to imagine that we would tolerate a similar scale of destruction on land, but because it happens at sea, the damage is largely hidden. On land, we have had a planning system for over 50 years to ... set aside areas for protection. Unless similar steps are taken at sea to allow recovery from decades of intensive fishing, species may disappear and the ecosystem itself be put in danger."

The report concludes that fishing is a threat to our seas, not only around the UK, but globally, and sets out a litany of the destruction that has been caused. Populations of more than 40 per cent of commercial fish species in the north-east Atlantic and neighbouring seas are below sustainable limits. Large quantities of unmarketable fish - in some cases up to 50 per cent of the catch - are discarded at sea.

Thousands of seabirds and marine mammals such as dolphins and porpoises are killed, getting tangled and drowning, in nets or caught on the hooks of "long-line" fishing gear.

The seabed has been destroyed over vast areas in the North Sea and other seas, and the myriad organisms that live there wiped out by beam-trawling, in which heavy gear is dragged along the bottom. Substantial marine nature reserves, off-limits to fishing boats, must now be the way out, the commission says. Britain is committed to setting up marine reserves over the next decade, but the call for 30 per cent of UK waters to be so dedicated is the first time anyone has put a precise number on the project.

Euan Dunn, the head of marine policy at the RSPB, said: "What the Royal Commission has done is to sharpen the debate by suggesting what size this network should be."

Sir Tom said that around the world there was evidence that creating marine reserves led to a several-fold increase in the size of fish, shellfish and other animals in a relatively few years. Commission members said implementing their recommendations would clearly lead to a further shrinkage of activity in UK fishing communities.

George McRae, the secretary of the Scottish White Fish Producers Association, said: "There are 20,000 kilometres of oil pipelines in the North Sea and on top of that there are oil platforms and rigs and all sorts of legitimate industrial activity, which have had a huge impact on the environment. I haven't heard any suggestion that these should be curtailed in any way."

Commission members accept that their recommendations are one thing, but getting them agreed by the European Commission in Brussels, where they would have to be implemented, is quite another. Commission member Professor Paul Ekins said: "We hope that it will not be necessary for there to be a complete collapse of fish stocks for someone to recognise that something radical needs to be done."

© 2004 Independent Digital (UK) Ltd