<P> Salmon spend their early life in rivers, and then swim out to sea where they live their adult lives and gain most of their body mass . When they have matured, they return to the rivers to spawn . Usually they return with uncanny precision to the natal river where they were born, and even to the very spawning ground of their birth . It is thought that, when they are in the ocean, they use magnetoception to locate the general position of their natal river, and once close to the river, that they use their sense of smell to home in on the river entrance and even their natal spawning ground . </P> <P> In northwest America, salmon is a keystone species, which means the impact they have on other life is greater than would be expected in relation to their biomass . The death of the salmon has important consequences, since it means significant nutrients in their carcasses, rich in nitrogen, sulfur, carbon and phosphorus, are transferred from the ocean to terrestrial wildlife such as bears and riparian woodlands adjacent to the rivers . This has knock - on effects not only for the next generation of salmon, but to every species living in the riparian zones the salmon reach . The nutrients can also be washed downstream into estuaries where they accumulate and provide further support for estuarine breeding birds . </P> <P> Most salmon are anadromous, a term which comes from the Greek anadromos, meaning "running upward". Anadromous fish grow up mostly in the saltwater in oceans . When they have matured they migrate or "run up" freshwater rivers to spawn in what is called the salmon run . </P> <P> Anadromous salmon are Northern Hemisphere fish that spend their ocean phase in either the Atlantic Ocean or the Pacific Ocean . They do not thrive in warm water . There is only one species of salmon found in the Atlantic, commonly called the Atlantic salmon . These salmon run up rivers on both sides of the ocean . Seven different species of salmon inhabit the Pacific (see table), and these are collectively referred to as Pacific salmon . Five of these species run up rivers on both sides of the Pacific, but two species are found only on the Asian side . In the early 19th century, Chinook salmon were successfully established in the Southern Hemisphere, far from their native range, in New Zealand rivers . Attempts to establish anadromous salmon elsewhere have not succeeded . </P>

Where do salmon spend most of their lives