From the Cohabit series
Many local populations of salmon (Salmo sp. and Oncorhynchus sp.) are endangered. Salmon spend their early life in rivers, and then swim out to sea where they live their adult lives. When mature, 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 their natal spawning ground.