Every single species of large wild fish has been caught so systematically over the past 50 years that 90 per cent of each type have disappeared, according to the first scientific study to assess the fish left in the global ocean.
And, from the tropics to the poles, those left in the sea are only one half to one fifth the size they were before industrialized fishing began in about 1950, says the study which appears as the cover story of today’s issue of the scientific journal Nature.
The study by marine biologists Ransom Myers of Dalhousie University in Halifax and Boris Worm of the Institute for Marine Science in Kiel, Germany, catalogues biological destruction that is unprecedented in its global scope and rapidity since the dinosaurs died out 65 million years ago. And it blasts the idea that the oceans have vast pools of uncaught fish waiting to be discovered.
"We have to quit thinking about the ocean as a blue frontier," said Dr. Myers, who is Killam Chair of Ocean Studies at Dalhousie. "What we have is a remnant."
Dr. Worm, who is the Emmy-Noether Fellow in Marine Ecology at the German institute, was more blunt. The entire global ocean, which makes up 70 per cent of the Earth’s surface, is no longer in even close to its natural state.
"It is now a man-made system," Dr. Worm said, adding that it may be less stable and is probably less predictable as a stabilizing force of the planet.
"We are tampering with the life-support system of the planet and that’s not a good thing to do."
A separate scientific study published yesterday by the Species Survival Commission of the Swiss-based World Conservation Union warned that other ocean creatures are faring no better than the big fish. Some of the smaller air-breathing cetaceans, the group that includes dolphins and porpoises, are also in critical danger, often because they are caught inadvertently along with fish by industrial fisheries. The Yangtze dolphin, for example, has been reduced to a couple of dozen individuals left in the world.
The Nature study on fish took 10 years and examined all major fisheries in the world in nine oceanic systems and on four continental shelves. The data from the open ocean came from Japanese fleets of long-line fisheries, in which hooks are set at regular intervals across vast kilometres of ocean at the same time. The study included the fish most prized as human foodstuff: tuna, marlin, swordfish, cod and halibut.
These fish, as well as sharks, are at the top of the ocean’s food chain, and their loss will have a profound effect — if an unpredictable one — on the whole ecosystem of the global ocean, Dr. Myers said.
Some species are perilously close to the point of no return, the study found. The ocean’s large sharks will die out unless the fishery catch in the planet’s open ocean falls by 50 to 60 per cent, Dr. Myers said. And many other species are also right on the brink. The phenomenon is driven by advances in technology such as the sonar methods developed during the Second World War and the satellite methods of finding the ocean’s warm fronts where fish once congregated.
Other scientific studies show that the ocean’s populations of big fish are now so depleted that people today spend far more time and energy to catch fewer fish than even a few years ago.
"One population by one population, we are pushing species to extinction," Dr. Myers said.
The fate of the Atlantic cod, with its population cut down to 1 per cent of the pre-1950 numbers, is unknown, one of the scariest signals of how unpredictable biological destruction on this level can be, Dr. Myers said. And the Pacific sardines are showing no signs of recovery either, he said.
But other species may recover if strong measures to cut levels of fishing are taken immediately, Dr. Worm said.