WWF estimates that about 75 per cent of fish stock in Europe is overfished and that if the practice continues nine out of 10 stocks will be at unsustainable levels by 2022. The practice was allowed to continue under the previous policy, so the introduction of maximum sustainable yield should go some way towards reversing that position.The main problem with the introduction of MSY, however, is that the data that we have for some stocks may be unreliable, and reliance on out of date or inaccurate data means that stocks could still be over or underfished.