However, it is not always possible to predict unexpected losses due to environmental catastrophes. So, overfishing may occur even when the calculations indicate safe levels of fishing. Guidelines and strategies intended to limit overfishing by American fisheries operations are a result of recommendations and policies established by governmental and independent fisheries agencies. Confining fishing to areas outside of breeding waters prevents overfishing. In addition, restrictions are placed on the age and number of fish and invertebrates caught during a fishing trip and season.
Negotiations permit fisheries to make a profit based on market prices.
Overfishing specifications do not protect the decimation of fish populations by lack of food, overpredation, and disease. Water pollution can create conditions that deplete plankton and other foods for smaller commercial fish. Drastic drops in food supply can cause a population crash if fish are caught under guidelines intended for a population with adequate food. Pollution can also cause unpredictable death of fish or decrease their reproductive rate. Overpredation is also a problem as marine mammals and sea birds hunt depleted fish populations with low food diversity.