Large Fish of the Ocean were NOT 90% Depleted by 1980

#fishmyths

This paper appeared in 2003 in the journal Nature. Primarily using catch per hook data from Japanese longline fisheries, the authors showed that the catch per hook had declined quite rapidly between 1960-1980 and was at about 10% of the initial values in 1980. A graph from the original paper is shown below

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The authors then argued that the catch per hook was a good index of the abundance of the population abundance and that by 1980 most of the large fish of the oceans were depleted to only 10% of their unfished abundance by 1980. The best available science shows that most tuna stocks remain above the target levels that will produce maximum sustainable yield.

This paper aroused a storm of controversy in the fisheries community because everyone who knew anything about the status of tuna stocks knew that the stocks were not depleted that much by 2003, let alone by 1980. Perhaps the most obvious problem with the assertion of the authors was that the catch of tuna and billfish increased 2.5 fold from 1980 to 2006. So how could the stocks have been depleted by 1980 and the catch still managed to increase so much?

The figure below from a 2006 paper in Science by John Sibert and co-authors shows the history of catches of major tuna stocks.

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Subsequently in 2011 Juan-Jorda and co authors published a paper in the journal Proceedings of the National Academy of Sciences showing that tuna stocks around the world were at about 50% of the abundance they had been before industrial fishing began. This is shown in the figure below.   By 1980 the tuna stocks were at 80% of their abundance before industrial fishing, not the 10% argued in the 2003 paper. Despite the obvious error there is a reference to the 90% depletion number almost weekly in the print and electronic media.

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Hampton, J., J. R. Sibert, P. Kleiber, M. N. Maunder, and S. J. Harley. 2005. Decline of Pacific tuna populations exaggerated? Nature 434:E1-E2.

Sibert, J., J. Hampton, P. Kleiber, and M. Maunder. 2006. Biomass, Size, and Trophic Status of Top Predators in the Pacific Ocean. Science 314:1773-1776.

Juan-Jorda, M. S., I. Mosqueira, A. B. Cooper, J. Freire, and N. K. Dulvy. 2011. Global population trajectories of tunas and their relatives. Proceedings of the National Academy of Sciences of the United States of America 108:20650-20655.