70% of the World's Fish Stocks are NOT Overfished
Daniel Pauly and colleagues at the Sea Around Us Project have repeatedly claimed 70% of world fish stocks are overexploited. They use catch data only and assume that any stock whose catch is less than ½ of the maximum catch that occurred earlier was overfished. The figure below from a 2007 paper by Pauly shows both the trend in stock status and a schematic of how catch data are used to calculate stock status.
This conclusion and entire approach have been subject to a long string of criticisms. The Food and Agriculture Organization of the United Nations assess the status of stocks and estimate that about 30% of global fish stocks are overexploited.
The figure below from the 2011 paper by Branch and co-authors shows the trend in overexploitation one estimates using catch compared to using scientific stock assessments for the same stocks. It shows that using scientific data the estimated proportion of stocks to be overexploited is about 30%.
Worm, B., R. Hilborn, J. K. Baum, T. A. Branch, J. S. Collie, C. Costello, M. J. Fogarty, E. A. Fulton, J. A. Hutchings, S. Jennings, O. P. Jensen, H. K. Lotze, P. M. Mace, T. R. McClanahan, C. Minto, S. R. Palumbi, A. Parma, D. Ricard, A. A. Rosenberg, R. Watson, and D. Zeller. 2009. Rebuilding Global Fisheries. Science 325:578-585.
Branch, T. A., O. P. Jensen, D. Ricard, Y. Ye, and R. Hilborn. 2011. Contrasting Global Trends in Marine Fishery Status Obtained from Catches and from Stock Assessments. Conservation Biology 25:777-786.