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"The world is withdrawing from a joint bank account of fish without knowing what has been withdrawn or the remaining balance," Pauly said.
One of the reasons for the discrepancy in the catch figures, Pauly and Zeller say, is that official totals greatly underestimate the size of artisanal and subsistence fisheries worldwide. To their surprise, they found that these accounted for 25 percent of total catches; they slightly increased over the study period as more people participated. The bulk of the decline over the last 20 years, however, was due to decreases in industrial fisheries.
"Our results indicate that the declining is very strong and the declining is not due to countries fishing less," Pauly said during a teleconference to announce the study. "It is due to the countries fishing too much and having exhausted one fish after the other."
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The study arose from skepticism over the completeness of FAO figures, largely due to the fact that they rely on national governments reporting their own tallies, which for political or other reasons they might not always be disposed to do accurately.