In the last 60 years, global fisheries have massively underestimated their catches. About 32 million tonnes (35 million tons) of fish a year might be unreported. However, catches are also declining more strongly than we thought. According to findings published in Nature Communications this week, the discrepancy might be due to countries focusing on large-scale, industrial fishing – and neglecting smaller operations.
The Food and Agriculture Organization of the United Nations (FAO) collects fisheries catch data from its member countries and makes this dataset available to scientists and policymakers. Based on the data FAO assembled, global marine fisheries catches increased to 86 million tonnes (95 million tons) in 1996, and then slightly declined by 0.38 million tonnes (0.42 million tons) per year to around 77 million tonnes (85 million tons) by 2010.
However, some member countries might be excluding data on the harder-to-track small-scale fisheries (such as artisanal, subsistence, or recreational fishing), as well as illegal catches and discarded fish. These instances are scored as “zero,” and they might not be an accurate reflection of the state of global fisheries.
So, University of British Columbia’s Daniel Pauly and Dirk Zeller turned to a technique called “catch reconstruction” and used published literature, statistics, and the help of local experts to fill in what’s missing. They amassed data from 1950 to 2010 with the help of 100 collaborators from dozens of institutions.
The Pew Charitable Trusts
Based on their estimates, catch actually peaked at 130 million tonnes (140 million tons) in 1996 and has declined 1.2 million tonnes (1.3 million tons) a year since. That means that overall, reconstructed catches are 53 percent higher than what reported data suggest. "The world is withdrawing from a joint bank account of fish without knowing what has been withdrawn or the remaining balance," Pauly says in a statement. "Better estimating the amount we're taking out can help ensure there is enough fish to sustain us in the future."
These differences, the researchers think, are mostly due to a greater decline in catches from industrial fishing. Discarded bycatch (generated mostly by shrimp trawling) have declined, while the artisanal sector continues to show gradual growth.
