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Why we've been hugely underestimating the overfishing of the oceans

  • Author: Chelsea Harvey
  • Updated: September 30, 2016
  • Published January 19, 2016

The state of the world's fish stocks may be in worse shape than official reports indicate, according to new data – a possibility with worrying consequences for both international food security and marine ecosystems.

A study published Tuesday in the journal Nature Communications suggests that the national data many countries have submitted to the UN's Food and Agriculture Organization (FAO) has not always accurately reflected the amount of fish actually caught over the past six decades. And the paper indicates that global fishing practices may have been even less sustainable over the past few decades than scientists previously thought.

The FAO's official data report that global marine fisheries catches peaked in 1996 at 86 million metric tons and have since slightly declined. But a collaborative effort from more than 50 institutions around the world has produced data that tell a different story altogether. The new data suggest that global catches actually peaked at 130 metric tons in 1996 and have declined sharply – on average, by about 1.2 million metric tons every year – ever since.

The effort was led by researchers Daniel Pauly and Dirk Zeller of the University of British Columbia's Sea Around Us project. The two were interested investigating the extent to which data submitted to the FAO was misrepresented or underreported.

Scientists had previously noticed, for instance, that when nations recorded "no data" for a given region or fishing sector, that value would be translated into a zero in FAO records – not always an accurate reflection of the actual catches that were made.

Additionally, recreational fishing, discarded bycatch (that is, fish that are caught and then thrown away for various reasons) and illegal fishing have often gone unreported by various nations, said Pauly during a Monday teleconference. "The result of this is that the catch is underestimated," he said.

So the researchers teamed up with partners all over the world to help them examine the official FAO data, identify areas where data might be missing or misrepresented and consult both existing literature and local experts and agencies to compile more accurate data. This is a method known as "catch reconstruction," and the researchers used it to examine all catches between 1950 and 2010.

Ultimately, they estimated that global catches during this time period were 50 percent higher than the FAO reported, peaking in the mid-1990s at 130 million metric tons, rather than the officially reported 86 million. As of 2010, the reconstructed data suggest that global catches amount to nearly 109 million metric tons, while the official data only report 77 million metric tons.

This news can be interpreted as both good and bad news. On the one hand, "it means that fisheries are more important than we think," Pauly said – in other words, when catches were at their highest, they were producing more food for the world than scientists previously thought. This is a plus for global food security in the authors' eyes. Overfishing and the subsequent decline of the world's fish stocks can be a threat to the food security of cultures that rely heavily on fish – but Pauly suggests that if we implement better management techniques in the future that allow these stocks to replenish themselves, we may be able to feed more people than we thought, as the new data suggest.

On the other hand, the higher catch numbers also suggest that fishing has been even more unsustainable in the past than scientists thought. And the world is now suffering the consequences, as the authors point out.

Their second major finding was that fish catches have been sharply declining from the 1990s up through 2010 – much more severely than the FAO has reported. At first, the authors thought that these declines might be due to increased restrictions by certain countries on fishing quotas in recent years. But when the researchers removed those countries from their calculations, they found that the catch data was still caught up in a downward trend.

"Our results indicate that the declining is very strong and the declining is not due to countries fishing less," Pauly said during the teleconference. "It is due to the countries fishing too much and having exhausted one fish after the other." The data indicate that the largest of these declines come from the industrial fishing sector.

To be clear, the research is not meant to assess the state of the world's fisheries, Pauly added – but, nonetheless, the study does raise some important questions about fisheries management moving forward.

The authors suggest that, in the future, the FAO might consider requiring nations to submit catch statistics separately for both large-scale and small-scale fisheries in order to ensure that small-scale fisheries don't fly under the radar. They also point out the importance of stock rebuilding – that is, enacting fishing quotas to cut down on overfishing and allow fish stocks to replenish themselves.

Such action may become even more important in the future, as additional factors – most notably, the effects of climate change – place even more pressure on global fish stocks, Pauly noted. "In the future there will be another mechanism that will begin to play a role [in catch declines] – that is global warming – and it will be very difficult to separate from the effects of fishing," he said.

So while a few countries have already implemented fishing caps, he predicted that the world will continue to see a sharp and continual decline in catch until better practices are enacted worldwide. And this will be important to consider, not only for the health of the oceans, but for the health of the millions of people worldwide who depend on fish for their food and their livelihoods.

With good management, though, there's room for optimism, Pauly suggested. "The fact that we catch far more than we thought is, if you like, a positive thing," he said during the teleconference. "If we rebuild stocks, we can rebuild to more than we thought before. Basically, the oceans are more productive than we thought before."

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