David Boyd used to make his living fishing cod off the coast of Newfoundland.

Now that the cod are gone, he runs the Prime Berth Fishing Museum in Twillingate, showing tourists how the biggest cod fishery in the world used to be run.

It's an object lesson in how the mighty have fallen. The cod that swam so densely 500 years ago that the first European fishermen could catch them by lowering buckets into the sea, are now so rare that Mr. Boyd often has trouble getting the few dozen he needs to show tourists how the great fishermen of old would split the fish.

The hell of it is to look back now knowing that Canada's biggest biological catastrophe was preventable. "The fish had no chance," Mr. Boyd says. "It's hard not to get cynical."

Of all the ecological mayhem that has happened in the 10 years since world leaders pledged at the Earth Summit in Rio de Janeiro to save the planet's diversity of species, the death of Canada's cod stands as a conspicuous example of failure. That's despite the fact that Canada was the first of 183 countries to sign the Biodiversity Convention in Rio and was rewarded with the international office, in Montreal, to oversee the protection of biodiversity.

Destruction of the cod has been so profound it is cited in international scientific literature as one of the worst environmental deaths of the modern era. From the early 1980s to 2001, Canada's northern cod population fell 99.9 per cent.

"It's always the one people raise at conferences and in scientific articles: 'We don't want things to go the way of Canada's cod,' " said Jeffrey Hutchings, a world authority on marine ecology who teaches at Dalhousie University in Halifax. "At the end of the day, we have what has become a classic example of biological catastrophe and Canada looks foolish."

And as world leaders gather once again to lament the state of the Earth -- this time in Johannesburg -- it is worth asking: Has Canada learned from its terrible mistake? Signs are that it has not.

Other Canadian fisheries have collapsed unceremoniously in the past decade while yet more are being pushed relentlessly to the edge. Pacific sardine, haddock, Bering wolffish, Atlantic halibut and yellowtail flounder have all been put on the international endangered-species list.

Pacific hake, a staple of such products as fish fingers, is being fished off Canada's West Coast these days far past its ability to replenish itself, said Josh Laughren, a marine specialist at the World Wildlife Fund. And the mighty northern cod itself -- off-limits to fisherman for the first time a month after the Rio summit ended in 1992 -- is still under attack.

Even though the cod are in worse shape now than in 1992, the federal government decided recently to allow fisherman to take 5,600 tonnes a year out of the fragile fishery.

"We're still fishing," Prof. Hutchings said. "Truly that has to be seen as inconsistent with the spirit of Rio."

Rio de Janeiro and Johannesburg feel a long way away when you're a fisherman in Twillingate, Newfoundland, piecing together the fall of the cod. As far as Mr. Boyd can see it, northern cod ought to have been the ultimate renewable resource.

They reproduce as fast as you can throw a hook. They have plenty of food out there off the coast of Newfoundland on Canada's continental shelf and not so many marine predators.

And the whole fishery had a history of booming success from 1497 when John Cabot discovered Newfoundland until the first signs in 1973 that the endless supply was dwindling.

In fact, the fishermen couldn't keep up with the fish, there were that many. Before refrigeration came to the fishing boats in the mid-1960s, they caught so many fish that they had to learn how to split the cod and salt it so it could be shipped around the world.

Cod-splitting is an ancient art, involving taking out the cod's sound bone, the bit of the fish that controls buoyancy. That allows the fish to be laid flat. Mr. Boyd remembers the most famous Twillingate cod-splitter of all time, Eric Boyd, who lives on in legend.

"He would give a little flick and before the sound bone struck the water, he had another one out," Mr. Boyd said.

Around the time refrigeration came, trawlers and draggers from Spain, the United States, Portugal, Japan and eventually Canada made their appearance. Through the 1960s, '70s and '80s, Newfoundland's Grand Banks supported so many of these big fishing fleets that it looked like a city out on the water, Mr. Boyd said.

"Some of them had more technology than a submarine," he said. "It took just 30 years to destroy the biomass, 1960 to 1990. The fish couldn't hide."

The highest reported catch was in 1968, when fishermen took 810,000 tonnes of cod. By 1973, the federal government tried to impose a quota for the first time, but set it so high, no one could meet it. Even then the fish stocks were on the way down.

In 1977, Canada banished international fishing boats to outside a 200-mile-limit off Newfoundland. But that's when Canada's big trawlers kicked into high gear, taking as much as 80 per cent of the remaining cod.

Biologically, the destruction was twofold, Prof. Hutchings said. First, the trawlers destroyed the ocean food chain, plowing through the seabeds and scooping up massive amounts of life, or biomass. Think of a vast forest, supporting all sorts of deer, songbirds and butterflies. When it's razed, everything dies.

"One of the rules [of marine ecology] is: make sure species abundance doesn't decline to historically low levels," Prof. Hutchings said. "We have allowed all kinds of species to decline to historically low levels. And when you change an ecosystem so dramatically, it's difficult to predict what the knockout effect will be for other species."

The second form of destruction sounds too silly to say. They fished so hard that they took out the fish that were capable of reproducing. By the end, the fishermen were taking only fish that had not yet had a chance to reproduce.

"That's clearly unsustainable," Prof. Hutchings said.

There was a bit of a respite from 1992 to 1998, while a moratorium stood. But when the federal government allowed a small fishery to reopen, it encouraged the use of the same gill nets that had earlier taken the bigger fish.

Mr. Boyd couldn't believe his eyes. He had written to the Department of Fisheries and Oceans, pleading with them make sure fishermen didn't use the same technology that had collapsed the stocks in the first place.

"I wrote to DFO: 'Whatever you do, don't use gill nets that take out the 15, 20, 25-pound cod,' " he said. "What did DFO do? Encouraged the use of big-mesh gill nets to take out all the breeders."

That was four years ago. The federal government's own surveys of cod stocks these days show no cod older than eight years. Cod don't mature and start to breed until six or seven.

"If they can't find any cod out there older than eight, that's something that's in extraordinarily terrible shape," Prof. Hutchings said.

But Canada is not alone in its belief in the "ghost of inexhaustibility past," as Prof. Hutchings puts it.

Leaders in Johannesburg will have to face up to other biological crises of the past decade, and earlier, spawned by human belief that nature has boundless ability to absorb damage.

Climate change, caused by greenhouse-gas pollution sent into the atmosphere, is worsening as the pollution intensifies. Scientists have warned that this holds out the potential of altering patterns of life over entire continents within decades.

Freshwater stores are being polluted, even as the human population that needs them grows. Critical forests in the Amazon continue to be cut.

The race for survival among plants and animals is far more urgent than that catalogued in 1992.

The 2000 edition of the Red List of Threatened Species, put together by the World Conservation Union (IUCN), showed that one in four mammal species and one in eight bird species faces a high risk of extinction in the near future. In total, 5,435 species of animals are at risk of dying out now, compared with 5,205 in 1996. Already, 816 species are known to have gone extinct or live only in zoos.

"Clearly, there is a documented deterioration of the status of species; clearly there is an extinction crisis before us," David Brackett, chairman of the IUCN's species survival commission, wrote in the 2000 report. "What the impact of this continued crisis will be has yet to be fully realized."

As for the cod, Prof. Hutchings fears it is now commercially extinct, just like the bison, though the latter is no longer hunted. And the billions of fish that once thronged an area half the size of Saskatchewan off the Grand Banks are so rare they have ceased being an ecological force in the ocean. Just like bison on the Great Plains.

"It takes time to realize they're not coming back," Prof. Hutchings said. Consumers have barely noticed the absence of one of the world's long-time food staples. Walleye pollock from Alaska has replaced cod in the grocers' freezers. The pollock stocks aren't doing well these days.

In Newfoundland, the fishermen are making lots of money from crab. And, Mr. Boyd said, they are talking about catching scuplin, the fish with the thorns nobody used to dream of eating, and sea urchins, so denigrated they've been dubbed "whore's eggs" in Newfoundland.

The other day, at the docks at Twillingate, Mr. Boyd encountered a ship carrying 200,000 pounds of capelin, a little fish that feeds cod, seals, whales and puffin. The fishermen had decided the capelin were too small and were throwing them back. All dead. Mr. Boyd said this kind of scene is going on all along the coast.

"It's happening over and over and over again," he said. "In 2002."

The road from Rio

Canada and the environment, 10 years after the Rio Earth Summit

-*Saturday: Attack of the alien species

-*Today: Fish depletion: Our great biological catastrophe

-*Tuesday: A Canadian city's bid to save the planet