As a result of overfishing, fish populations decline and formerly productive fisheries may be forced to close. Long-term costs of overfishing can also include social dislocation due to loss of jobs, lost biological diversity and ecosystem collapse.

History already provides too much evidence of the hazards of overfishing. A prime example of this kind of excess is the situation of the Atlantic herring. In New England, factory trawlers flocked to the Georges Bank in the early-to-mid 1960s. Record catches of cod, herring, haddock and silver hake were followed by steep declines in these species. The populations of these commercially exploited groundfish and flounder declined by almost 70 percent between 1963 and 1974, dropping to the lowest levels ever observed. There are also currently warning signs, from the perspective of single stocks as well as the overall ecosystem, that overfishing is occurring in the North Pacific. In particular, the pollock stocks in the Eastern Bering Sea and the Aleutian Islands have faced a serious decline, as have several species of marine mammals and seabirds that depend on pollock for food.