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A commercial fishing boat begins harvesting herring off the central coast of B.C.

Courtesy Pacific Wild

The world's fishing fleets have taken a 50-per-cent larger catch from the ocean ecosystem than official numbers suggest, a new study out of the University of British Columbia reveals.

If accurate, the result has far-reaching consequences for conservation and fisheries management, because the under-reporting may be hiding significant declines in global fish stocks.

Describing what he calls "systemic underestimation," Daniel Pauly, a professor and lead author of the study, said there are multiple reasons for the discrepancy. "What is not reported are illegal fisheries," he said, adding that other factors include "the artisanal fisheries, the small-scale fisheries that sell their fish, fishers that eat the fish themselves, and recreational fisheries."

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Discarded fish that never make it to port aren't typically factored in either, he added.

All countries, along with their industries, are responsible for reporting the amount of fish they catch to the Food and Agriculture Organization of the United Nations. The organization is the only international institution keeping tabs on global fishery statistics.

Experts have long thought the organization's numbers don't represent a complete picture, but the size of the discrepancy is unknown.

To address this, UBC researchers used a method known as "catch reconstruction," tapping into other sources of information – from regional data to expert assessments – to come up with more realistic estimates of fish catches.

The analysis, published Tuesday in the journal Nature Communications, presents a wide gap between the organization's numbers and the reconstructed total over the period between 1950 and 2010.

The analysis suggests that before 1996, countries around the world pulled fish from oceans at a greater annual rate than was reported by the UN. The discovery of new stocks of fish from the 1950s to 1990s propelled an increase in the overall global catch, even as stocks were being depleted one after the other.

In 1996, fish catching peaked. The organization recorded 86 million tonnes of fish caught. Researchers, however, discovered 130 million tonnes – a disparity of 44 million tonnes of fish that year. By then, newly exploited stocks were no longer keeping up with the loss of fish populations elsewhere, and a period of decline began.

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"In other words," Dr. Pauly said, "it was never really sustainable."

After 1996, the UN figures show the global catch constant or declining slightly, but the UBC study found that the actual catches were likely dropping off more steeply – an effect that was disguised by under-reporting.

Jeff Hutchings, a fisheries biologist at Dalhousie University in Halifax who was not involved in the analysis, said the results suggest that the impact of overfishing has been more severe than is generally perceived.

"We already know that many stocks were overfished in the northwest Atlantic through the 1950s to the 1970s, and this suggests the magnitude of overfishing is much greater than we thought it was," he said.

Dr. Pauly called for fishing countries to implement quotas and reduce their take to allow resources to replenish. "If we rebuild stocks, we can rebuild to more than we thought before," he said. "Basically, the oceans are more productive than we thought."

He added that global warming adds an additional source of stress to fish populations that can be expected to increasingly affect and complicate efforts to manage fisheries globally.

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"This is beginning to impact us, and it will lead to decline that we have assessed to be about 30 to 50 per cent in the tropical areas of the world," he said. "It will be very hard to separate that from overfishing."

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