With their numbers decreasing by as much as 80 percent in 15 years, the depleted communities could crash delicately balanced ecosystems, with unknown worldwide consequences, the surveyors of pelagic creatures warned.
"More than 90 percent of the fish we like to eat are gone," said Jeremy Jackson, a renowned marine ecologist at the Scripps Institution of Oceanography in La Jolla, Calif., who was not involved in the study.
The statistics -- which some industry scientists questioned -- emerged from a 10-year analysis of trawler surveys and U.S. and Japanese long-line fishing records compiled over 47 years for 62 predatory species.
"From giant blue marlin to mighty bluefin tuna and from tropical groupers to Antarctic cod, industrial fishing has scoured the global ocean," said lead study author Ransom Myers, Killam Chair in Ocean Studies at Dalhousie University in Halifax, Nova Scotia. "There is no blue frontier left."
The sampling included fish inhabiting every ocean save the seas surrounding Earth's poles and those that dwell where continents submerge under the sea off the coasts of Newfoundland, Thailand and Antarctica.
"Since 1950, with the onset of industrialized 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," said study co-author Boris Worm of Dalhousie and the University of Kiel in Germany.
Some industry scientists conceded that overfishing was a problem, but minimized its magnitude.
"The paper may be criticized vigorously because of some serious errors in the analysis," said Norm Bartoo, who conducts stock assessments on tunas and billfish at the Southwest Fisheries Science Center in La Jolla, the regional research arm of the National Marine Fisheries Service.
He expressed doubt that fishing rates, areas and gear remained constant throughout the survey period, as the results seemed to imply.
The study appeared to target areas with previously known fish declines, said marine biologist Lorne Clayton, executive director of the Canadian Highly Migratory Species Foundation, established by the B.C. Tuna Fishermen's Association to promote and conduct industry research of migratory fish in the Pacific Ocean.
Clayton said in a telephone interview he thought the authors should have taken into account natural population fluctuations driven by changes in environment and temperature, such as those triggered by the water-warming El Niño phenomenon that carries global weather consequences.
However, Louis Botsford, wildlife, fish and conservation biologist at the University of California, Davis, assessed the study as "very credible."
"Even if the authors' numbers are off by as much as 50 percent, this is a big, big problem," said Randy Kochevar, science communications manager for the Monterey, Calif., Bay Aquarium and principal investigator with the Tagging of Pacific Pelagics research project, an international collaboration to study migration patterns of large open-ocean animals in the North Pacific.
"The trends they've identified have profound consequences for the future of ocean life," he told United Press International.
The analysis, which will be published in the May 15 issue of the British journal Nature, is the first to show general, pronounced declines of entire communities across widely varying ecosystems, the scale of which many scientists may not realize, the authors said.
"We have forgotten what we used to have," Jackson said. "We had oceans full of heroic fish -- literally sea monsters. People used to harpoon 3-meter-long swordfish in rowboats."
Most of the decimation took place in the early years of exploiting the ocean's food supplies, before the days of survey-taking, the researchers said. Modern trend analyses, they noted, do not include pre-industrial-fishing figures as the baseline from which to draw conclusions about survival patterns.
"The impact we have had on ocean ecosystems has been vastly underestimated," Worm told UPI.
The great fish are meeting the fate of other great beasts that were hunted to the brink of extinction, and beyond, researchers said.
"Industrial whaling, for example, reduced many large whales by a factor of 10 or more in a relative short time frame, the North American bison was reduced from 30 million to less than 1,000 in a few decades, the passenger pigeon, from many billions to zero during the same time," Worm said. "I think we need to understand just how good we are at killing large numbers of animals."
Even the open ocean, widely viewed as an untapped reservoir of large fish, has suffered severe depletion, the researchers found.
"The long-lining data tell a story we have not heard before," said Daniel Pauly, a fisheries scientist from the University of British Columbia who pioneered techniques of gathering global fish information.
In this technique, particularly favored by Japanese fleets, single-stranded fishing lines hoist endless rows of baited hooks over vast stretches of open ocean that can extend thousands of miles.
"Whereas long lines used to catch 10 fish per 100 hooks, now they are lucky to catch one," Myers said.
"We know so little about these powerful and mysterious fish," said Barbara Block, a Stanford University professor of marine sciences and a principal investigator with TOPP. "We could eliminate these populations before we have a chance to understand them."
Recognizing a growing problem, 192 nations meeting at the U.N.-sanctioned World Summit on Sustainable Development last fall in Johannesburg, South Africa, urged restoration of depleted fish stocks to levels that can provide maximum sustainable yield by 2015.
The study results should serve as the "missing baseline" for restoring fisheries and marine ecosystems to healthy levels, Myers and Worm said.
Conservation efforts have had mixed results, noted Rich Ruais, executive director of the East Coast Tuna Association in Salem, N.H.
"Are there still problems of illegal, unregulated, unreported fishing?" Ruais asked in a telephone interview. "Absolutely there are as there are still subsidies that are problematic."
However, there are also success stories such as the International Convention for the Conservation of Atlantic Tunas, a commercial treaty involving 33 countries that is conducting ground-breaking work to blow pirate fishing out of the water, he told UPI.
In its annual fisheries report to Congress, released Tuesday, the National Oceanic and Atmospheric Association pointed to strides made last year in sustaining America's marine fish stocks. The report noted an additional fish stock was fully rebuilt, four species were taken off the overfished list and 70 overfished varieties continued to recover under federal rebuilding plans.
"We think about the oceans as being a source of endless bounty, and look on the idea of hunting animals to extinction as a folly from the distant past," Kochevar told UPI. "The fact is that ocean ecosystems are fragile, and we're using cutting-edge technologies to empty them of life in ways the buffalo hunters of the American West could never have imagined."
"The need for more knowledge is both urgent and critical," he concluded. "And in the meantime, we all need to proceed with caution!"
(Editors: UPI photos WAX2003051201, WAX2003051202 and WAX2003051203 are available)
Notable deaths of 2014 [PHOTOS]