Global Fisheries Catch Declining, Despite Statistics

Countries’ improvements to their fisheries statistics have been contributing to the false impression that humanity is getting more and more fish from the ocean when, in reality, global marine catches have been declining on average by around 1.2 million tons per year since 1996.

A new study explains why reconstructed catch data from the Sea Around Us, an initiative by the University of British Columbia and the University of Western Australia, show declining fish catches, while the Food and Agriculture Organization of the United Nations claims that catches have been more or less stable since the 1990s. 

The problem, says the authors, occurs as an inadvertent side effect of well-intentioned efforts by countries to improve their national data monitoring and reporting systems. As they include new information, for example of a previously unmonitored or poorly-monitored fishery, region or fleet, these new data add additional catches to those of already monitored sectors, thus creating the impression of a growing trend. But such upward tendencies in catches do not match reality in most countries, because often national statistical systems do not correct their new numbers retroactively.  

“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,” says Dirk Zeller, lead author of the study, from the University of Western Australia. “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.”

This means that when Mozambique submitted its data to the U.N. agency, they were already biased as neither the country’s statistical agency nor FAO insisted on undertaking retroactive adjustments. According to the researchers, many countries’ statistics have the same issue.

Incomplete time series influenced by the bias is what leads FAO to claim that fisheries catches peaked at 86 million tons in 1996 and kept growing until stabilizing at around 91 million tons per year. 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 tons in 1996 but also led to a sharp plunge in catches, which have decreased to about 110 million tons in recent years.

Zeller emphasizes that countries’ efforts to improve the collection of fisheries statistics are highly commendable and should be encouraged. However, retroactive corrections that go as far back in time as any fishing activity existed ought to be made at the same time to avoid disseminating misleading fisheries trends. 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.