A study by Ransom Myers and Boris Worm of  Dalhousie University has 
shown that changes in the fish stocks are changing more rapidly than 
generally believed.  According to their paper in the latest issue of 
Nature, the biomass of large predators (usually the most valuable species) 
in a new fishery is reduced on average by 80% within 15 years.  Dr. Worm 
acknowledges uncertainty in their data but says if anything the data are 
conservative.  Theory suggests that the maximum sustainable yield that can 
be cropped from a fishery comes when the biomass of a target species is 
about 50% of its original yield.  Most fisheries are well below that.

Source: The Economist, May 17.


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