Big-Fish Stocks Fall 90 Percent Since 1950, Study Says
National Geographic News
|May 15, 2003|
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."
"This is because we have forgotten what we used to have," said Jeremy Jackson of the Scripps Institution of Oceanography. "We had oceans full of heroic fishliterally sea monsters. People used to harpoon three-meter long swordfish in rowboats. Hemingway's Old Man and the Sea was for real."
Myers and Worm said that the tendency in fisheries biology to use only the most recent data increased the problem of shifting baselines. These great fish are not only declining in numbers, but with intense fishing pressure they can never attain the sizes they once did. "Where detailed data are available we see that the average size of these top predators is only one-fifth to one-half of what is used to be. The few blue marlin today reach one-fifth of the weight they once had. In many cases, the fish caught today are under such intense fishing pressure, they never even have the chance to reproduce," said Myers.
In the 1980s Myers was a fisheries biologist with the Department of Fisheries and Oceans in Newfoundland. "No one understood how fast the decline happened at the endit was only a couple of years," says Myers. "The quotas had been too high. They refused to slow down because they had seen lots of little fish coming ina good year class. The little fish were caught and discarded and there was no future."
Fisheries' Stability Compromised Worldwide
Myers said the most recent findings raise critical questions at a much larger scale. "This isn't about just about one species," he said. "The sustainability of fisheries is being severely compromised worldwide."
At the Johannesburg World Summit on Sustainable Development last year, 192 Nations called on the global community to restore world fisheries stocks to levels that can provide maximum sustainable yield by 2015. The authors of this comprehensive new study say their results provide the "missing baseline" needed to restore fisheries and marine ecosystems to healthy levels.
Without this baseline information, most scientists and managers are hardly aware of the profound magnitude of change that took place at the beginning of almost every major fishery, they say. As a result, managers today are working hard to stabilize the last 10 percentoften unaware that the virgin biomass of their fishery was once ten times greater.
But there is some good news too: "In most regions we saw increases in faster-growing species which seemed to fill in for overfished stocks. This points to the recovery potential for the community at large," Worm said. "But unfortunately we often switch fishing pressure to species that are doing well, and drive them down in turn. This sabotages recovery."
The solution to this global problem is simple, said the scientists, yet it is extremely hard to do in practice. Recovery requires overall reduction of fishing mortality (the percentage of fish killed each year). This includes reducing quotas, reducing overall effort, cutting subsidies, reducing bycatch, and creating networks of marine reserves.
"A minimum reduction of 50 percent of fishing mortality may be necessary to avoid further declines of particularly sensitive species," Myers said. "If stocks were restored to higher abundance, we could get just as much fish out of the ocean by putting in only one-third to one-tenth of the effort. It would be difficult for fishermen initiallybut they will see the gains in the long run."
"We are in massive denial and continue to bicker over the last shrinking numbers of survivors, employing satellites and sensors to catch the last fish left," said Myers. "We have to understand how close to extinction some of these populations really are. And we must act now, before they have reached the point of no return. I want there to be hammerhead sharks and bluefin tuna around when my five-year-old son grows up. If present fishing levels persist, these great fish will go the way of the dinosaurs."
Sylvia Earle said the new research may have come just in time to awaken people to the seriousness of the situation. "We will never get back to what we had in the oceans 50 years ago, but we still have a small window of opportunity to save the last few big fish before they are exterminated," she said.
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