Scientists believe the overfishing that has caused the demise of the traditional catch of fish, such as cod and plaice, is now causing an equally severe, long-term decline of more exotic, deep-water species.
Research into five North Atlantic species of deep-sea fish has found that their numbers have fallen dramatically during the relatively short time since trawlers began to exploit new deepwater fishing grounds off Canada.
Similar trends have been observed off the coasts of Britain and Europe, where commercial trawlers have turned increasingly to deepwater species over the past two decades, such as the orange roughy, which can live for 150 years and take 25 years to reach sexual maturity.
Scientists in Canada said yesterday the decline in numbers has caused many deep-sea fish to be deemed "critically endangered" under the international rules on threatened species.
Jennifer Devine, Krista Baker and Richard Haedrich of Memorial University in St John's, Newfoundland, analysed the declining catch of deepwater species caught during a 17-year period in the Canadian waters of the north-west Atlantic.
They analysed the five species in detail because they all live on, or near the bottom of the sea floor. None of the species were taken in any substantial number prior to the 1970s. The scientists found that all five declined by between 87 per cent and 98 per cent over 17 years. They extrapolated these figures to cover a period of three generations of the long-lived fish and concluded that the real decline is nearer to 99 per cent.
"According to the IUCN [International Conservation Union] criteria, these five species qualify as critically endangered in the north-west Atlantic. The declines occurred on a timescale equal to, or slightly less than, a single generation," the scientists report in the journal Nature.
The species - roundnose grenadier, blue hake, spiny eel, spinytail skate and onion-eye grenadier - share many characteristics of all deep-sea fish.
They are long-lived, with a lifespan of about 60 years or more, and take 20 years or more to reach sexual maturity. All those features make them vulnerable to extinction when fished commercially, said Professor Haedrich.
"The deep sea covers an enormous area of the world and it was thought to be a place you can turn to for more fishing reserves. This is absolutely not true," he said.
His colleague, Jennifer Devine, said that the study was one of the first to analyse the effect of the trend towards harvesting deeper-water stocks.
"We know that fish communities in shallower waters have been damaged due to overfishing and other environmental factors but no one has really looked at the deep sea," Ms Devine said.
"There's a lot going on out there that's not really been taken notice of. One step that should be enacted is the protection of deep-sea habitats," she said.
Richard Dixon, director WWF Scotland, said that the slow growth rates of deep-sea fish - some of which live for as long as 150 years - make them highly vulnerable to overfishing.
"With such long lifespans, the impact of modern fishing methods on these deep-sea species is disastrous, as they can be wiped out of entire areas within a single season," Dr Dixon said.
"There is a real danger that slow-growing, deepwater species will take centuries to recover from current fishing, if they can at all. In European waters, we should close deep-sea fisheries as a matter of urgency," he said.
Deep-sea fisheries are those below 400m and, in Europe, the main species of commercial interest are the orange roughy, the roundnose grenadier, argentines and deep-water sharks such as the Portuguese dogfish.
In 1989, French trawlers discovered major fishing grounds for orange roughy off the west coast of Scotland and the catch peaked at 3,600 tons in 1991. Three years later, that fell to just 180 tons and now stocks are believed to be fished out.
According to the WWF, the orange roughy fishery has virtually collapsed in 20 years in European waters, argentines crashed in the Irish deepwater fishery in 1990, roundnose grenadiers suffer very high levels of juvenile mortality in trawls. For many species stocks are unknown.
"Whilst some of our commercial species such as mackerel and plaice could recover within years given proper management, there is a real danger that slow-growing, deep-water species will take centuries to recover, if at all," said Claire Pescod, Marine Policy Officer for WWF Scotland.
Some populations of deep-water sharks off Britain have declined by 80 per cent in just 10 years, Ms Pescod said. "We must act to close these fisheries as a matter of extreme urgency."
Fishing by numbers
* The global annual total of wild fish caught in 1950: 20 million tons
* The global annual total of wild fish caught in 2001: 92 million tons
* Number of fishing boats in the world: 3.5 million
* The population decline of deep- sea five species in 17 years: 98 per cent
* Quantity of cod caught in the Atlantic Ocean in 1956: 2.1 million tons
* Quantity of cod caught in the Atlantic Ocean in 2004: 645,000 tons
* Proportion of the North Sea floor trawled at least once a year: 90 per cent
* Proportion of the total global fish catchthat comes from deep-sea species: 1 per cent
* Number of new fish species found on two deep-sea reefs in 2005: 750
* Number of dolphins and p
orpoises that are killed as "by-catch" in the North Atlantic every year: 10,000
* Proportion of deep sea coral reefs considered to be severely damaged: 67 per cent
* Proportion of deep-sea coral reefs considered to be
damaged beyond recovery:
20 per cent
* Number of acres of reef estimated to have been destroyed in the past 30 years: 35 million
* The proportion of the adult cod population aged above five: 0.5 per cent.
* Percentage of cod less than two years old: 90 per cent
* Contribution of fishing to the GNP of the European Union: 1 per cent
* The proportion of European Union budget dedicated to Common Fisheries Policy in 2004: 0.75 per cent
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