Most of us like eating fish, but nobody wants to cuddle them. The consequence is that, while otters, seals, elephants, rhinos and even foxes have powerful political constituencies to fight for them, mankind is doing disastrous things at sea without anybody seeming to care much.

Environmental organisations often damage their own causes by overstatement. I am among those who have criticised Greenpeace and its brethren for abusing statistics and indulging in some pretty wild scaremongering. But Greenpeace is absolutely right, in its report published last week, to highlight the scandal of some supermarkets - Asda is branded the worst offender - selling threatened fish species.

The world's oceans are being plundered, and nobody seems willing or able to stop the slaughter. Some fish and crustaceans are successfully farmed: trout and oysters, to name but two. Stocks of others are sustainable, such as herring, sardines, whitebait and mussels. Many species, however, are in desperate trouble, including tuna, plaice, monkfish and cod. Over the past half-century, the world's annual fish catch has risen from 18m tonnes to 95m. The latest figures from the UN's Food and Agriculture Organisation suggest that 52% of commercial fish species are fully exploited, 17% overexploited and 8% depleted.

It is striking to contrast the wave of alarm, if not panic, sweeping the world about avian flu with our indifference to the plight of fish. As long as there are fillets in the shops, we buy them. When species vanish, people shrug and eat something else.

Two important recent books have detailed the world's fishery crisis - Michael Wigan's Last of the Hunter Gatherers, in 1998, and Charles Clover's End of the Line, in 2004. Both tell the same horror story, but neither has prompted useful political reaction. Wigan quotes a Scottish saying, from the days when God was feared. If herring deserted a locality, fisherfolk said, it was because of "the wickedness of the people". In a rather different sense from that intended, the old sages have proved right. Clover invites us to imagine how the world would react if a mile-wide net attached to a steel bar were dragged across the plains of Africa, scooping up or destroying everything in its path - lions, cheetahs, rhinos, elephants, impalas and warthogs. This, he says, is what modern trawlers are doing every day in the oceans of the world.

One-third of the total catch is discarded - dead - as commercially worthless. Nets flatten reefs and aquatic plants. Laws on catch sizes are routinely flouted. Industrial netsmen are estimated to reduce any newly discovered fish community to one-tenth of its size within a decade. Ever bigger boats, with ever more monstrously "efficient" equipment, attack diminishing shoals of fish. Ireland's new super-trawler, Atlantic Dawn, is the biggest such vessel ever built, and accounts for one-third of the nation's fishing capacity. Off northern Scotland, birds and fish are suffering from the near genocide of the sand-eels they eat, taken by netsmen for fishmeal.

Crazily, for social reasons most governments underwrite the killing. Japan is top of the annual subsidy league (£1.4bn) followed by the EU (£644m) and the US (£617m). Individual EU nations, headed by Spain, France, Ireland and Italy, give additional top-ups.

Charles Clover writes: "The fact that the sea is presided over by lunatics who believe there should be commercial fishing in 100% of the sea breeds a culture that is corrosive. Two erroneous beliefs have been allowed to flourish. First, that you can cheat biology. Second, that you can keep people happy in far-flung communities in the west of Ireland, Scotland and Spain by allowing them to fish, when the gallop of technology means that this year maybe only half a dozen people in the village can fish sustainably, and next year it will be four."

Anyone who thinks national governments behave uniquely selfishly about pollution or trade should take a look at the record on fishing. No minister wants to have a row with his country's few but allegedly romantic commercial catchers. Captain Birdseye will make a formidable fuss, and the public cares nothing for the plight of his scaly victims. There is a persistent nationalistic belief that excesses are only committed by others - the Spanish and Japanese dominate our own demonology. In truth, there are no innocents. All netsmen are striving to claw a living amid rising costs and declining stocks. Inspections are so inadequate in many places that nobody is effectively monitoring atrocities attested by a wealth of anecdotage.

One of the few modest recovery stories is that of the Atlantic salmon. This is the almost single-handed achievement of an Icelander, Orri Vigfusson. Despairing at the plight of a fish he loves, 15 years ago he started the North Atlantic Salmon Fund. Its record in curbing commercial fishing, buying out drift-netters and lobbying governments is astonishing.

Cynics say that Vigfusson makes headway only because he has won the backing of rich sportsmen who like to catch salmon with rod and line. But part of his campaign has been the promotion of catch-and-release. Many rivers now get the income from sport anglers, while their fish survive. The consequence of Vigfusson's crusade is a precarious but undoubted revival in the fortunes of the Atlantic salmon. He will take another notable step forward if he succeeds in his campaign to restrict salmon farming, which has done terrible ecological damage in Scotland and Norway.

Yet salmon is only one, relatively privileged, species. The poor cod has no such smart friends, and we have almost done for it. Newfoundland employed 44,000 people in fishing and processing until the catastrophic collapse of the early 1990s. Further south, there is deepening concern about tuna, and some shark and marlin species. Most experts agree that the only hope of restoring some sanity to the world's fisheries is to end the dominant influence of the commercial industry. To an extraordinary extent, governments dance to a tune called by those who make their living catching fish.

Charles Clover observes that British net-fishing today employs about as many people as lawnmower manufacturing, yet historic sentiment gives it amazing clout. The situation is much worse in Ireland and Spain, chronic exponents of reckless policy. EU officials claim that matters are improving, that excesses are being contained. Few experts believe them.

All credit to Greenpeace for identifying the simple thing each of us can do, to fight back against the threat to the oceans: buy fish from Marks & Spencer or Waitrose. These stores, according to the new survey, have by far the best record of selling sustainable and legitimately sourced species.

We need to start caring about fish, not easy when they lack fur, soulful eyes and other attributes that make amateur greens go gooey about selected fauna. But what is happening every day in the oceans is as great a scandal as elephant and rhino murder on Africa's plains. If it continues, the consequences for our descendants will be even more bitter.