The journey of the salmon has fascinated people for centuries. The fish hatches in freshwater rivers but soon travels to the sea. No matter how far it goes, the salmon returns years later to its birth area to breed. For some salmon, this can mean a trip of more than 2,000 miles (3,200 kilometers). The fish is even willing to leap over waterfalls and cut through churning rapids to reach its home waters again. Salmon belong to the family Salmonidae, which also includes the trout. Where salmon liveThe most common types of salmon are the Atlantic salmon, of which there is one species, and the Pacific salmon, of which there are several species. Atlantic salmon live in the North Atlantic Ocean. They are native to the rivers of Europe and North America. Pacific salmon are found in the mild and Arctic waters of the North Pacific. They breed in rivers near both the North American and Asian coasts. Physical featuresSalmon come in a range of sizes. The small Pacific pink (or humpback) salmon, for example, generally weighs between 3 and 6 pounds (1.4 and 2.7 kilograms). The Pacific king (or chinook) salmon, on the other hand, averages about 20–25 pounds (9–11 kilograms). Some king salmon weigh more than 100 pounds (45 kilograms). While in the ocean, salmon have a silver sheen and spots on their back and fins. During the breeding season, however, they undergo a change in coloration that varies from one species to another. Also during this period, the jaws of male salmon become hooked. The males use their jaws to fight other salmon when competing for a mate. These changes in appearance are most striking in male Pacific salmon. Life cycleSalmon spend the first part of their lives in freshwater. A newly hatched salmon eats from a yolk sac attached to the underside of its body. When the yolk is gone, the fish wriggles up through the gravel in which it was hatched. Young salmon of some species head out to sea immediately. Others stay around their birthplace for a period of a few weeks to a few years. Salmon grow quickly in the sea while feeding mostly on other fish. They migrate to the site of their birth to breed after a period of usually one to three years. Scientists are not sure exactly how salmon find their way back to their birthplace. The fish may use the position of the sun to guide them. As they get closer to their destination, they seem to depend heavily on their sense of smell. Research has shown that salmon apparently can recognize the scent of the water from their original route to the ocean. A salmon is in great condition when it leaves the ocean to start its journey home. Once in freshwater, however, the fish stops eating and lives off its body fat. As it fights its way upstream, it becomes thin and worn out. Then, in this battered condition, a male has to fight for a mate. After a male and a female are paired, the female begins the act of reproduction by digging a pit in a gravel bed. There she lays thousands of eggs. At the same time, the male releases his sperm to fertilize the eggs. The female then covers the eggs with gravel. The eggs hatch anywhere from 60 to 200 days later. After breeding, the salmon are exhausted. They weigh only about 60–70 percent of what they did in the sea. Most adult Pacific salmon die shortly after reproduction. Many Atlantic salmon, however, return to the sea and may breed again. Effects of human activitySalmon are commercially important to humans because they are a popular food fish. They are sold fresh, frozen, smoked, or canned. Over the years, salmon populations have declined because of human activities. In some areas, people have simply taken too many salmon from the oceans and rivers. Elsewhere, water pollution has damaged salmon habitats. Another major threat has been human interference with salmon breeding grounds and their routes to breeding places through the construction of dams and other structures. |