“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 industrialised fisheries, we have rapidly reduced the resource base to less than 10 percent — not 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. "These are the megafauna, 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 industrialised fishing to the present. To measure the decline in open ocean ecosystems, the researchers gained access to Japanese longlining data. The Japanese fleet is the most widespread fishing operation in the world, covering all oceans except the cirumpolar seas.
"The longlining data tells 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 – like a hole burning through paper. As the hole expands, the edge is where the fisheries concentrate, until there is nowhere left to go. 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."
“I have heard that the record price for a bluefin tuna, a 200-kilogram specimen, was US$180,000,” Earle said. “This kind of exploitation is not driven by the starving masses, but by high-end appetites. I belive that even when there is only one bluefish tuna left in the sea, someone will pay a million dollars to be able to eat it.”
Earle, who has written several books about ocean conservation, and was once named a Time magazine "Hero for the Planet," said very few people understand the extent and implications of the over-exploitation of the ocean, or just how much life had disappeared from the sea in the last 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 our survival, but also because the big predatory fish are full of the toxins and other pollutants that we cast into the oceans."
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 they have forgotten what we used to have," said Jeremy Jackson, of the Scripps Institution of Oceanography. "We had oceans full of heroic fish — literally sea monsters. People used to harpoon three-metre long swordfish in rowboats. Hemingway's Old Man and the Sea was for real."
These great fish are not only declining in numbers. "Where detailed data is available, we see that the average size of these top predators is only one-half to one-fifth of what is used to be,” said Myers. “In many cases, the fish caught today are under such intense fishing pressure, they haven’t had the chance to reproduce."
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 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 remain ignorant of the magnitude of the changes that have taken place in recent decades. Managers today are working hard to stabilise the last 10 percent—often unaware that the virgin biomass of their fishery was once ten times greater.
The solution to this global problem is simple, said the scientists – yet it is extremely hard to put into practice. Recovery requires a significant 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 greater 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 fishers initially – but they will see the gains in the long run.”