There's nowhere left to go fishing!

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We have run out of places to fish, according to research published in a recent issue of the online journal PLoS ONE.

The study by Wilf Swartz and coauthors arrived as this conclusion by measuring the ecological footprint of fisheries and charting the systematic expansion of industrialised fisheries from 1950 to 2005.

To measure the ecological footprint of fisheries, the authors used estimates of the primary productivity (the amount of energy produced by the organisms at the base of the food chain such as phytoplankton) required to support fisheries catches. This is similar to calculating the amount of grass that would be required per year to generate a certain production of milk or meat.

The authors found that industrialised fisheries had expanded to cover most of the world’s productive waters by 2005. They found that the southward expansion of fisheries (from the coastal waters off the North Atlantic and Northwest Pacific into the high seas and southward into the Southern Hemisphere) occurred at a rate of almost one degree of latitude (about 111 km) per year, with the greatest period of expansion occurring in the 1980s and early 1990s.

By the mid 1990s, a third of the world's ocean, and two-thirds of continental shelves, were heavily exploited, leaving only unproductive waters of the high seas (ie. the open waters of the oceans and seas outside of national jurisdiction), and the relatively inaccessible waters in the Arctic and Antarctic as the last remaining areas open to exploitation.  

During this period, global catches increased nearly five-fold, from 19 million tons in 1950, and peaking to 90 million tons in the late 1980s and decreasing since to 87 million tons in 2005.  The worrying trend is that the slow decrease of about a half million tons per year since the peak has not been reversed, and is not likely to ever be.

"The era of great expansion has come to an end, and maintaining the current supply of wild fish sustainably is not possible," said co-author Enric Sala. "The sooner we come to grips with it — similar to how society has recognised the effects of climate change — the sooner we can stop the downward spiral by creating stricter fisheries regulations and more marine reserves."

For more information, see the paper: Swartz, W, E Sala, S Tracey, R Watson and D Pauly (2010) The spatial expansion and ecological footprint of fisheries (1950 to present). PLoS ONE 5, e15143 doi:10.1371/journal.pone.0015143