Industrial fishing fleets have systematically stripped 90% of the giant tuna, swordfish, marlin and other big fish from the world's oceans, according to a new study that suggests the virtual collapse of these stocks -- such as happened to the cod off New England -- is a distinct possibility.
Fishing fleets are now competing for the remnants -- about 10% -- of the biggest fish in the oceans, concludes a 10-year research project reported in today's issue of the science journal Nature.
"Fishermen used to go out and catch these phenomenally big fish," said Ransom A. Myers, a fisheries biologist at Dalhousie University in Halifax, Canada. "But they cannot find them anymore. They're not there. We ate them."
If the current level of overfishing continues, the new study suggests, fish populations will soon become too small to be sustainable, causing fisheries to disappear. That, in turn, could have a serious impact on human food supplies and cause long-term damage to the ocean environment.
"We know that current fishing practices will lead to the collapse of fisheries and eventually extinction of various species," said Myers, whose previous warnings about the imminent collapse of Atlantic cod populations were ignored. "By any measure, there are way too many hooks in the water."
Myers' study, with Dalhousie University colleague Boris Worm, is the third in a series of recent scientific papers that challenge the notion that the oceans are so resilient they can provide an inexhaustible supply of fish to feed the world.
The first study, by Jeremy Jackson of the Scripps Institution of Oceanography in La Jolla, Calif., looked at the decline of many ocean species over several centuries and documented how it set in motion the collapse of kelp forests and coral reefs.
The second study, by Daniel Pauly of the University of British Columbia, focused on how the worldwide catch of all seafood has been on the decline since the late 1980s, as evidenced by the ever-dwindling catches of an expanding global fishing fleet.
Myers' study focused on how the introduction of industrial fishing in the years immediately after World War II caused the demise of what was once considered "the blue frontier." It was then that most of the biggest fish were pulled from the sea, never to rebound because of continuing fishing pressure. These oceanic giants are now mostly memories, romanticized in novels such as Ernest Hemingway's "The Old Man and the Sea," or in yellowing photos of fishermen beside their enormous catches.
The loss of these fish presents a considerable problem for fishery managers from the 192 nations that signed a declaration last year at a United Nations summit to restore fish to healthy levels by 2015.
Pauly said the new study shows that in most places, fisheries managers are arriving too late. He likens the situation to saving a forest after harvesting has taken place.
"It's like we have a forest of stumps," Pauly said. "We are trying to manage a forest of stumps."
Tuna industry scientists immediately challenged the study's conclusions, saying they were simplistic and inconsistent with other data.
"Their analysis has several implicit assumptions that are either unsupported or weakly supported," said Mark Maunder, a fisheries expert with the Inter-American Tropical Tuna Commission in La Jolla. A group of top tuna scientists, he said, would be scrutinizing the study and would issue a formal rebuttal later.
"No doubt scientists will quibble over the details," said Andy Rosenberg, former deputy director of the National Marine Fisheries Service and now a dean at the University of New Hampshire. "But the study shows we can very rapidly deplete a broad range of species even in the largest and deepest oceans. The bottom line is we are killing too many fish."
In the study, Myers and Worm analyzed 47 years of detailed fishing records kept by the Japanese long-lining fleet, in which ships unfurl baited hooks from lines that stretch up to 50 miles off their sterns.
The Japanese pioneered long lining after World War II. In the first few years after the war, the Japanese fleet was forbidden to leave the waters immediately around Japan, but later was permitted to spread across the Pacific, Indian and Atlantic oceans. Other fishing fleets adopted the same technique and other methods of fishing designed to greatly increase their catch.
"Anytime [the Japanese] went into new areas, they caught 10 big fish per 100 hooks," Myers said, "and then quickly it would decline to one fish per 100 hooks."
The decline was remarkably consistent in every new fishing ground: Most of the big fish were gone within 10 to 15 years of fishing, which mostly occurred in the 1950s, '60s and '70s.
The Japanese data, combined with data from fishermen using nets, provided the first glimpse of a global decline, the researchers said. And rather than collecting data on one type of fish, the researchers were able to examine a vast array of big fish caught with hooks and nets.
The largest bluefin tuna, albacore, blue marlin, swordfish, cod and halibut are not the only species to decline from industrial fishing, the researchers said. Many non-targeted species, such as sharks, turtles and other accidental catch, also have dropped sharply.
"A consistent picture emerges only if you look at everything at once," said Worm. "You see that there is no blue frontier left. The declines are everywhere, even in very remote areas."