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. Fish diseases also appear to be on the increase, causing unpredicted population decreases. Recent data analyses collected by these agencies show some disturbing, as well hopeful, trends in the northeastern fishing waters. Data collected on several commercial fish such as haddock and plaice indicate current overfishing practices. The haddock population at this point is overfished, meaning that its population could reach critically low numbers.