A new study says 90 percent of the large predatory fish species have vanished from the world's oceans since the onset of largescale commercial fishing 50 years ago. Scientists warn that unless restoration is attempted on a global scale, fish populations and the ocean ecosystems they support are in danger of even further collapse. Marine ecologist Ransom Myers from Dalhousie University in Nova Scotia was the lead author of the study. He set out to find the answer to one question "How many and what variety of fish were there in the ocean before exploitation began?"
The study reported published in the journal Nature surveyed harvest data from global fisheries over the last past 50 years and plotted the results. "What we found all over the world [was] the same pattern. Initially the biomass - which means the number and weight of the total fish community - was ten times higher than it is now, and the declines were enormous, on the order of 10 to 15 percent a year initially. So with industrial exploitation the whole community declined very, very rapidly and reaches an equilibrium of about 10 percent of its original number," Mr. Myers said.
Ransom Myers said the problem is that commercial fishing trawlers typically use longlines with 100 baited hooks to catch tuna, marlin, cod, haddock and other predatory fish. Fifty years ago, trawlers could pull in ten fish on a single longline. They're likely to catch only one per line today. Mr. Myers said an industrial operation can reduce a fish community by 80 percent within 15 years.
"Humans are enormously good at killing animals, and if you fish in an unregulated way the animals decline very, very rapidly. Now, I should say that I am not against industrial fishing per se. Where it is regulated - for example, in the great fisheries of the Alaskan shelf - you have a very productive system where all the bio-diversity appears to be maintained. They have even taken methods to protect the deep-sea corals and deep-sea sponges that are usually not protected in the world's oceans.
Mr. Myers elaborted on the statistic that 90 percent of global fishing communities have been reduced by industrial fishing. "Individual species may have declined much greater," he pointed out, "and may be [heading] toward extinction, whereas other species have increased," he explained.
"[A good example] is off the southern banks of Newfoundland, [where] we had a great fishery for haddock when trawling first started," he said. "There were one million tons of haddock in a relatively small area, and within 15 years this species was almost driven to extinction and now remains maybe one thousandth or a millionth of its original abundance, really truly very, very low numbers. And that species hasn't returned because it is caught as a bycatch when you catch other species."
When asked if he was surprised with the results of his study, in which data was gathered for 10 years, Mr. Myers said, "I was surprised initially, but as I looked at more and more data, it became more the norm and [there was] a consistency in the results of this 10-fold decline in the total fish community. I think that many scientists and many individuals are surprised because we lose our memory of large fish in the past. For instance, in the North Sea and off the Coast of Norway, who would have thought that there were these great fisheries for blue marlin? People there don't think that blue marlin exist. Similarly in the Gulf of Mexico, the white tip shark is considered a very rare species, where fifty years ago it was enormously abundant, perhaps 1,000-fold greater. So we as humans we are not only good at fishing, we are good at forgetting our past." While some critics say that the data exaggerates the decline in global fisheries, Jeremy Jackson, a marine biologist with Scripps Institute of Oceanography, said the numbers reported in the paper are most likely understated. "These results are so clear and straight forward and striking. One of the reasons I think that [the paper] is so conservative is that all of those data that they use begin only in the 1950s or the 1960s. These are all fishes that we fished in great abundance for thousands of years beforehand. So, any interpretation of the data of Myers and Worm has to be made in the context of that earlier depletion." While the study makes no recommendations, Ransom Myers said the solution to the global problem is simple: Catch fewer fish, reduce the bycatch, cut subsidies and quotas. He said that political will and common sense must also come into play.
The United Nations Summit on sustainable development in Johannesburg last year called for restoration of global fisheries to sustainable levels by 2015. Mr. Myers said his study offers a baseline for that restoration effort and warned, "If present fishing levels persist, these great fish will go the way of the dinosaurs."