Atlantic salmon can reach the impressive length of 120cm when mature. Although much of their adult life is spent at sea, salmon return to the precise freshwater tributary in which they were born, even leaping up waterfalls to reach their destination. How they return to the same spot is unknown, although odour has been suggested as playing an important role in this process. After spawning in shallow gravel beds most adults die and their young in turn migrate to sea after a couple of years.