The oceans are emptying. In a single generation, once thriving populations of deep sea fish have been driven to the brink of extinction by expanding fisheries, researchers said yesterday.
Records of catches logged by trawlers operating in the North Atlantic from 1978 to 1994 show that at least five species of deep sea fish are at such low levels that they qualify for the World Conservation Union's critically endangered list.
The research, published in the journal Nature, adds weight to demands by conservationists for the creation of internationally protected reserves to place vast areas of the deep seas out of bounds to fisheries.
"We expected to see declines, but we didn't expect such severe declines," said Jennifer Devine, who led the study at Memorial University in Newfoundland, Canada. "If nothing changes, we could be facing barren oceans or oceans of fish we can't utilize."
Last year, researchers in Canada, led by Ransom Myers at Dalhousie University, reported that the great predators, such as tuna, swordfish and marlin, were in serious decline. Shark populations have also plummeted in the North Atlantic, by 90 percent in 15 years.
While previous studies focused largely on species destined for the dinner plate, the latest research looked at by-catch, those fish caught up in trawlers' nets by accident.
"These are species no one really cares about, but they play a key role in the ecosystem," Devine said.
The scientists reviewed trawler logs for records of five deep sea by-catch species -- the roundnose grenadier, onion-eye grenadier, blue hake, spiny eel and spinytail skate. All are slow growing, reaching more than 1m long and living to 60 years. They found that levels of all the fish plummeted by 87 percent to 98 percent over the 17 years, a rate that will see a decline over the next three generations of 99 percent to 100 percent.
Records for roundnose grenadier and onion-eye grenadier from 1995 to 2003 show those species have collapsed by 99.6 percent and 93.3 percent in 26 years.
"The declines occurred on timescales equal to, or slightly less than, a single generation of these species," the authors wrote.
The researchers also checked the trawlers' logs for trends in the size of fish caught. Of the five by-catch species, four became progressively smaller over the 17 year period, by 25 percent to 57 percent, suggesting the fisheries were driving down the size of the fish that remain in the oceans.
The sharp decline in by-catch species has alarmed conservationists, who point out that fisheries have only expanded into the deep seas in recent decades, after near-shore stocks dropped below profitable levels.
"We now have the technology to fish down below 2km, something that has been brought in on a large scale in the North Atlantic in the past 15 years," said Myers.
He added: "What's alarming is we're eliminating fish we don't know much about at all and they are often the biggest conservation concern. If you're fishing for cod and you fail to catch any, you can quit fishing for it and hope stocks recover, but no one pays attention to the by-catch, so they can be fished out without anyone picking up on it."
The crash of fish populations is a spur to governments to rein in fisheries and seek out international agreements on deep sea marine reserves, Devine said.