Fish farms in these areas also produce much Pacific salmon. Sport fishing for salmon is popular in the United States and Canada. Coastal waters, lakes, and rivers in many parts of the world have been stocked with salmon. But transplanted salmon thrive only in a few places, such as the Great Lakes and New Zealand. Salmon conservation is based on the theory that a certain number of fish, called the escapement, should be allowed to spawn in each stream.
Fishing is regulated to ensure the proper escapement.
Conservation programs must also overcome such obstacles as dams, irrigation ditches, and pollution. In many areas, including northwestern North America, overfishing and other factors have sharply cut the salmon populations. The most important advance in conservation has been the development of improved hatcheries. These hatcheries, helped by increasing knowledge of fish nutrition and diseases, can produce thousands of healthy salmon to restock rivers and streams. Other conservation efforts have resulted in new designs for dams and fish ladders.