Global seafood catches, according to Sea Around Us. (Mapa: Sea Around Us)
Incorrect statistics create 'false impression' of global increase in fish catch
Friday, February 09, 2018, 03:00 (GMT + 9)
Fisheries statistics from different countries have been giving a false impression that more and more fish are caught, when reality indicates that global marine catches have been declining on average by around 1.2 million tonnes per year since 1996, concludes a study from Sea Around Us.
The investigation carried out by the research initiative at the University of British Columbia and the University of Western Australia, published in Marine Policy, shows a decline on fish catches. However, FAO claims that catches have been more or less ‘stable’ since the 1990s.
The authors of the study, Dirk Zeller and Daniel Pauly, argue that misinformation is due to an unintended side effect of well-intentioned efforts by countries to improve their national data monitoring and reporting systems. They explain that by providing new information -for example, from fisheries, regions or fleets that were not previously monitored or controlled in a precarious manner-, they add additional catches to those of the sectors already monitored, and thus create the impression of a growing trend.
“In our paper, we use the example of Mozambique where officials reported that small-scale catches ‘grew’ by 800 per cent from 2003 to 2004. This is incorrect. What happened was that the small-scale sector was massively under-represented in the reported data for the longest time and when a new reporting scheme was put in place in the early 2000s, improved catch data by the always-present subsistence and artisanal fisheries were added. A very similar amount of fish was caught in previous years, it was just not registered in the reported data,” says Zeller.
According to the researchers, the same is happening with statistics that come from many other countries.
“The problem is that these data are assembled by FAO and presented as global trends in the widely used State of the World Fisheries and Aquaculture report. But by not accounting for the presentist bias over an entire reported data history, FAO is misinterpreting trends,” says Pauly, Principal Investigator of the Sea Around Us at the University of British Columbia.
FAO claims that fisheries catches peaked at 86 million tonnes in 1996 and kept growing until stabilizing at around 91 million tonnes per year. However, Sea Around Us researchers say that this data is not accurate, due to incomplete time series influenced by the presentist bias.
Sea Around Us data accounting for both reported and unreported catches show, on the other hand, that overfishing allowed for a peak number of 130 million tonnes in 1996 but also led to a sharp plunge in catches, which have decreased to about 110 million tonnes in recent years.
The scientists suggest using methods such as the Sea Around Us’ catch reconstruction approach to fill gaps with best estimates of unreported catches based on harmonized data and information from a wide range of sources.