Independent study tallies 'true catch' of global fishing

Tens of millions more metric tonnes of fish have been taken from the seas than are recorded in official statistics, suggests a huge and controversial project aiming to estimate the “true catch” of the world’s fishing industry.

The work is detailed in a paper in Nature Communications by fisheries researchers Daniel Pauly and Dirk Zeller of the University of British Columbia in Vancouver, and it builds on a decade long project that has drawn in hundreds of researchers from around the world.

According to Daniel and Dirk, global fisheries catches hit a peak of 130 million metric tonnes (143.3 million tonnes) a year in 1996, and they have been declining strongly since then. This is substantially higher than the data collected by the Food and Agriculture Organisation (FAO) of the United Nations, which report that catches reached 86 million metric tonnes (94.8 million tonnes) in 1996 and have fallen only slightly. This decline is due at least in part to collapses in some fish stocks, says Daniel .

Fishing for data

The FAO numbers have long been the only estimate of how many metric tonnes of fish are caught at a global level. But “the FAO doesn’t have a mandate to correct the data they get,” Daniel told journalists during a conference call. This leaves the organisation reliant mainly on the numbers submitted by member countries, he says, and “the countries have the bad habit to report only the data they see.” This means that many official statistics do not account for a huge amount of the world’s fisheries catch, such as that by small-scale and subsistence fisheries or fish thrown back as “discards” — species other than those being hunted.

To fill in the holes in official statistics, Daniel’s team embarked on an epic project to supplement the official baseline data from member nations. This included using results from peer-reviewed research, interviews with local specialists and consumption information from population surveys. The international effort has already produced scores of papers — many of them co-authored by Daniel — concerning individual countries. For example, one study has estimated that Senegal’s catch is more than twice as large as the official FAO numbers. Some fisheries researchers, however, have questioned Daniel’s catch-reconstruction methods. He has also engaged in a sometimes-heated debate about whether data from catches can shed light on the state of fish populations remaining in the ocean.

Daniel also feels that his team has had to jump through hoops to publish the paper. He notes that the paper has very large uncertainty levels on the graph detailing the key findings of the paper. In fact, he says, the team had come up with relatively narrow confidence intervals by using a popular statistical method known as Monte Carlo. But one reviewer objected and, Daniel says, forced the use of a different method that gives “absurdly large confidence intervals.” “In reality, given that our country estimates are independent (we made sure of that), some will be too high, some too low and things will cancel out, and thus generate narrow confidence intervals,” Daniel wrote in an email to Nature. Overall, however, he is happy to point to the simple message of the research: “The catch of the world is higher than reported.”

In a statement, the FAO welcomed the paper, saying that “the idea of catch reconstructions has merit” and noting that the reconstruction work builds in part on FAO data. The FAO adds that it has some “technical reservations” about the trends identified but “agrees with the basic conclusions of the paper: Catch statistics (including estimates of additional sources of removals) can and should be improved, and this requires additional funding and international collaboration and country commitment.”