Only 10 percent of all large fishboth open ocean species including tuna, swordfish, marlin and the large groundfish such as cod, halibut, skates and flounderare left in the sea, according to research published in today's issue of the scientific journal Nature.
"From giant blue marlin to mighty bluefin tuna, and from tropical groupers to Antarctic cod, industrial fishing has scoured the global ocean. There is no blue frontier left," said lead author Ransom Myers, a fisheries biologist based at Dalhousie University in Canada. "Since 1950, with the onset of industrialized fisheries, we have rapidly reduced the resource base to less than 10 percentnot just in some areas, not just for some stocks, but for entire communities of these large fish species from the tropics to the poles."
"The impact we have had on ocean ecosystems has been vastly underestimated," said co-author Boris Worm of Dalhousie University and the University of Kiel in Germany. "These are the megafauna, the big predators of the sea, and the species we most value. Their depletion not only threatens the future of these fish and the fishers that depend on them, it could also bring about a complete re-organization of ocean ecosystems, with unknown global consequences."
The researchers collected data representing all major fisheries in the world, calculating population size and composition of large predatory fish communities from four continental shelves and nine oceanic systems, from the beginning of exploitation to the present. For shelf ecosystems they used data from standardized research trawl surveys to track the decline in the populations of large fishes.
To measure the decline in open ocean ecosystems, the researchers gained access to Japanese longlining data. Pelagic longlines are the most widespread fishing gear, and the Japanese fleet the most widespread longline operation, covering all oceans except the circumpolar seas. Longlines catch a wide range of species in a consistent way over vast areas. "Whereas longlines used to catch ten fish per a hundred hooks, now they are lucky to catch one," said Myers.
"The longlining data tell a story we have not heard before. It is coherent and consistent throughout, and it comes from a single source," said Daniel Pauly, a fisheries scientist from the University of British Columbia. It shows how Japanese longlining has expanded globally. It is like a hole burning through paper. As the hole expands, the edge is where the fisheries concentrate until there is nowhere left to go. Because longlining technology has improved, the authors estimates are conservative. If the catch rate has dropped by a factor of ten and the technology has improved, the declines are even greater than they are saying."
Marine biologist and National Geographic Explorer-in-Residence Sylvia Earle said the latest research proved what she had known and been warning about for many years. "I don't blame the fishermen for this," she said. "We, the consumers, have done this because we have a taste for fish and 'delicacies' such as shark-fin soup. Our demand for seafood appears to be insatiable."
Even as fish stocks dwindled, Earle said, it remained commercially viable for fishermen to go after what was left because certain markets were willing to pay enormous prices for some kinds of fish. "I have heard that the record for a bluefin tuna, a 440-pound (200-kilogram) specimen, sold for $180,000. So this kind of exploitation is not for the starving millions, but driven by high-end appetites. I've always believed that even when there is only one bluefin tuna left in the sea someone will pay a million dollars to be able to eat it."
Another cause of over-exploitation, Earle said, was billions of dollars governments spent subsidizing their fishing industries, trying to protect jobs and a way of life of communities. "But what is not realized is that when the fish have gone, the way of life will come to an end anyway. What's happening is not sustainable," she said.
Earle, who has written several books about ocean conservation and was once named a Time magazine "Hero for the Planet," said very people understood the extent and implications of the over-exploitation of the ocean, or just how much life had disappeared from the sea in 50 years. "Most people also don't know how bad it is for us to be eating so much fish, not only because of the destruction of an ecosystem vital to survival but also because the big predatory fish are full of the toxins and other pollutants that we cast into the oceans. It's not as healthy to eat fish as most people believe."
Fisheries Managers Are Skeptical
Myers and Worm sent their findings to many of the top fisheries scientists in the world for review. "We found there was acceptance of the overall pattern of rapid depletion of communities, but there was more controversy when it came to the current status of individual species, particularly with respect to tuna," said Myers. "Understandably, some fisheries managers find it very hard to accept."
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