Environmentalists say the North Sea is facing a crisis but those accused of causing it say the situation is over-exaggerated. Where does the truth lie? In the first of a two-part series, John Dean looks at the environmentalists' claims.

THEY may only make up 0.002 per cent of the world's marine surface area, but the wild waters of the North Sea are regarded as one of the planet's most productive for wildlife.

Now there are grave warnings that the sea is facing a crisis which has eradicated some species and is pushing others to the brink of extinction.

Environmental organisations including Greenpeace and the Wildlife Trusts, the umbrella organisation for wildlife trusts across the country, say the damage done over the past 40 years means all governments with coastlines along the North Sea need to improve protection.

Those blamed for causing damage, however, point to the work they have done over recent years to reduce pollution and disturbance and, in some cases, dispute the extent to which species are threatened.

The case for the prosecution, mounted in separate recent reports by Greenpeace and the Wildlife Trusts, includes:

l Overfishing: according to Greenpeace, North Sea herring and mackerel catches have collapsed since the 1960s and cod has been reduced to one sixth of its 1970s level; the Wildlife Trusts says fish stocks have declined by 35 per cent in just 25 years, the common skate is in desperate trouble and halibut, haddock and monkfish have suffered serious declines;

l Industrial pollution: discharged into rivers and estuaries and absorbed into animals' bodies; in addition to damage to fish, Greenpeace says the presence of pollutants reduces seals' ability to fight fatal illnesses such as phocine distemper virus, which claimed so many lives in 1988 and 2002;

l Agricultural pollution: fertilisers washed into streams and rivers off fields can cause potentially devastating eutrophication, which can also be caused by fall-out from vehicle exhausts and excessively enriches the nutrients in the sea. This leads to huge growth of algae, which removes the oxygen needed for sea creatures to survive;

l Ships routinely flushing out oil and chemical tanks and ballast tanks: with 200,000 ships crossing the North Sea every year, the risk is high, according to Greenpeace, not just from deliberate releases but also accidental loss of hazardous cargoes.

l Dredging for sand and gravel for the construction industry: the organisations say this has caused severe damage for shallower areas, constantly destroying seabed habitats which take years to recover; in addition, some North Sea areas, according to the Wildlife Trusts, are trawled by fishing nets up to 400 times a year, making it almost impossible for many creatures to re-establish colonies;

l Climate change: North Sea water temperatures are rising but shifts in global flows could, in time, cause a potentially catastrophic cooling, according to Greenpeace.

l Unrestricted development... of sustainable energy developments such as coastal windfarms, which the Wildlife Trusts wants to see regulated. Head of marine policy Joan Edwards said: "We know that any development offshore has an impact on the marine biodiversity and can have an negative effect. The sea is dynamic and if you do something in one place it can have an effect elsewhere. Renewable developments are being fast-tracked at the moment but there is not a planning system for the marine environment, no process to say this is what is proposed, is it in the right place, should it go elsewhere?"

According to both organisations, the cumulative effect has been devastating for the North Sea, which is home to 230 species of fish as well as sponges, sea urchins, shellfish, larger creatures such as harbour porpoises and dolphins, and, where, at most times, ten million seabirds are present.

Over-fishing remains one of their biggest concerns. Although only covering 000.2 per cent of the world's marine surface area, the North Sea provides four per cent of fish landed by trawler fleets.

Greenpeace says annual catches were stable at one million ton-nes from the start of the 20th century to the start of the Second World War, after which amounts increased dramatically due to new technologies which have made fishing fleets more efficient, partly because they could better locate shoals and partly because vessels were much larger and could carry bigger catches taken by huge seabed trawl nets.

Cod illustrates the point, according to Greenpeace, which says the estimated spawning stock has declined from 250,000 tonnes in the 1970s to 40,000 tonnes in 2001.

Greenpeace is also concerned that vast amounts of fish are discarded, an estimated 720,000 tonnes a year in the North Sea, and that the likes of porpoises and dolphins can be accidentally caught in nets.

The pressure group's oceans campaigner Oliver Knowles said: "Politicians are failing to protect the North Sea. For fisheries to be sustained long-term there need to be healthy fish populations. Fishing needs to be sustainable wherever it takes place if we are not to empty the oceans of fish and other marine life."

It seems a grave prosecution case to answer - but those for the defence argue that it may be over-exaggerated.

TOMORROW: In the concluding part of the series, John Dean examines the other side to the argument and initiatives to reduce the threat to wildlife habitats