The fishmonger - or more likely nowadays, the fish counter at Tesco's - has a fabulous array of fish. Here are mackerel from Cornwall, there are Dover sole from the English Channel, herring from the North Sea … true, they all seem smaller than they used to be, but look, there's orange roughy from the tropics, and blue whiting from the vasty deeps.

Then there is salmon, down in price again this week - and nobody can say they're getting smaller. You can buy them as big as you like.

Ah, yes, salmon. There is a simple rule about salmon; eating farmed salmon is bad for you, while eating wild salmon is bad for the fish.

Lord knows what's gone into that bargain salmon on the slab, with its diet of anti-sealice chemicals, its poorly formed tail (a giveaway) and dull skin. Pay up for a magnificent silver wild salmon, on the other hand, and you are helping to destroy one of nature's finest creations.

The wild salmon on the slab encapsulates the disaster that is overtaking the world's fishing industry. It probably comes from Ireland and, if so, it was almost certainly caught in a monofilament drift net. These vast devices are strung across miles of sea, where the salmon run from the north Atlantic, round the coast of Ireland towards the famous salmon rivers of Scotland and northern Europe.

They don't have a chance. The nets are invisible in water, and all but the smallest fish are caught. The more they struggle, the more they enmesh themselves. The seals are presented with an all-they-can-eat smorgasbord from the net (which is why seal numbers are soaring), and the fishermen have a harvest of silver.

The Irish drift-netters are doing fine, thanks. Catches are good, so what's the problem?

Simple. Every other nation has agreed to stop the carnage, to give salmon numbers a chance to recover. Ireland has refused to do so, despite the clear economic gain from such a move.

A study commissioned by the Irish government concluded that, in 2002, each salmon caught in a drift net was worth £14, while a salmon caught by a sport fisherman was worth £250, when his hotel, transport, equipment and fishing fees were added in.

The 30,000 fish caught on a line were worth three times as much as the 180,000 netted salmon. They used to say that, if you couldn't catch fish in Ireland, you should give up; it's not quite too late for that to be true again, if only the Irish government would see what is in its country's best economic interest.

Your Irish, netted, wild salmon are cheap because they are so easy to catch. They run where their instinct tells them, and the industrial fishermen are waiting. The fish have no answer to the technology of bigger boats, mile-long invisible nets and sonar searchers.

As with salmon, so with most of the fish species on the planet. The burgeoning technology means they have nowhere to hide and, as long as there are some left, the fishing boats will find them, and bring them cheaply to Cap'n Birdseye's factory or Asda's counter.

When a species is all gone, well, there are plenty more fish in the sea, and the new technology is brought to bear somewhere else - most recently, off the west coast of Africa.

The sea is astonishingly resilient, but there are limits. The Canadians had hunted cod, once a super-abundant species, to the brink of extinction off the Grand Banks. In 1992, they finally called a halt, to allow the stocks to recover. Twelve years on, the cod have not recovered, and some marine scientists argue that they never will. Other, less palatable species have moved into the ecological niche they once occupied.

On this side of the Atlantic, the pillage continues, helped by the Common Fisheries Policy, surely one of the most lunatic policies ever to emerge from the Brussels asylum. Whatever it was supposed to do, the effect of the CFP is to encourage the European Union's industrial fishing boats to grab whatever they can, while stocks last.

There are a few glimmers of light in the gloom. Iceland's prosperity is built on fish (which is why the Icelanders desperately needed to win the cod wars against the British) and its 200-mile limit is rigorously enforced.

The fishing is closely monitored and controlled, and the fishermen "own" areas. They can decide not to fish, confident that others will be kept out and that the fish will be bigger next year. New Zealand has a similar system. Neither is perfect, but both are oceans away from the rape of the seas which is the result of the CFP.

Short of reform of this shameful policy - and we all know that reforming anything in the EU is almost impossible - here is a suggestion for combating some of the netting. The Gulf of Mexico contains sunken battle tanks and surplus ships. These have provided a key for reefs to grow, and their presence has made trawling the seabed impossible. By the time the tanks rust away, the reef is self-sustaining. Already, there has been an explosion of marine life, and hugely valuable sport fishing for big fish.

There's no reason except the blind prejudice of the environmental lobby why something similar is not possible in the north Atlantic. As the North Sea oil platforms reach the end of their lives, they could be dumped in a pattern to provide a haven for marine life.

The trawlers would stay away for fear of losing their nets, so there would be no need for the sort of nightmare rules that have turned commercial fishermen into form-fillers. A really daring proposal would see the platforms turned into a fishing destination for adventurous sport fishermen, who would come for the giant fish that would soon emerge in the sanctuary.

Sport sea-fishermen in Britain could do with a break. They take a trivial proportion of the fish landed, bring jobs and enjoyment to coastal towns, and now they are being threatened with the need to pay £22 a year for a licence, a tax that will certainly cost more to administer and police than it will raise.

It makes you want to slap Margaret Beckett, the minister in charge of Dreadful Defra, in the face with a wet halibut - except that we really should leave this poor fish alone.

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