to the sea surface currents that transport them back to their natal river. It is a major misconception that salmon swim thousands of kilometres at sea; instead they surf through sea surface currents. It is possible they find their natal river by smell, although this is not confirmed; only 5% of Atlantic salmon go up the wrong river. The range of an individual Atlantic salmon can thus be the river where they are born and the sea surface currents that are connected to that river in a circular path. Wild salmon continued to disappear from many rivers during the twentieth century due to overfishing and habitat change. Ecology Diet Young salmon begin a feeding response within a few days. After the yolk sac is absorbed by the body, they begin to hunt. Juveniles start with tiny invertebrates, but as they mature, they may occasionally eat small fish. During this time, they hunt both in the substrate and in the current. Some have been known to eat salmon eggs. Plankton such as euphausiids are important food for pre-grilse but amphipods and decapods are also consumed. The most commonly eaten foods include caddisflies, blackflies, mayflies, stoneflies, and chironomids, as well as terrestrial insects. As adults, the salmon prefer capelin as their meal of choice. Capelin are elongated silvery fish that grow up to long. Other fish consumed include herring, alewives, smelts, scomberids, sand lance, and small cod. Behavior Fry and parr have been said to be territorial, but evidence showing them to guard territories is inconclusive. While they may occasionally be aggressive towards each other, the social hierarchy is still unclear. Many have been found to school, especially when leaving the estuary. Adult Atlantic salmon are considered much more aggressive than other salmon, and are more likely to attack other fish than others. Life stages Most Atlantic salmon follow an anadromous migration pattern, in that they undergo their greatest feeding and growth in saltwater; however, adults return to spawn in native freshwater streams where the eggs hatch and juveniles grow through several distinct stages. Atlantic salmon do not require saltwater. Numerous examples of fully freshwater (i.e., "landlocked") populations of the species exist throughout the Northern Hemisphere, including a now extinct population in Lake Ontario, which have been shown in recent studies to have spent their entire life cycle in watershed of the lake. In North America, the landlocked strains are frequently known