In the period from 1950 to the late 1980s, global catches in fishers have increased from less than 20 million tons per year to about 80 million tons per year. They have not increased anymore, which must be due to fish stocks that cannot deliver more fish and are already over-fished. A yield curve is shown with increasing, maximum and decreasing yield, as well as the equilibrium yield. Increasing effort will increase the yield until there is a maximum sustainable yield, which the United Nations has agreed is the target for all fisheries worldwide according to the Maximum Sustainable Yield Principle. This curve can also be interpreted in monetary terms; the point where the the cost curve and the equilibrium yield curve interest is where fishing is not profitable. The maximum economic yield is the target for fisheries, but this is not always sustainable; therefore there is a strong incentive for illegal fishing and overfishing. If fishing is subsidized, the environmental concerns are even more pronounced.
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