The natural range of the Atlantic salmon (Salmo salar) stretches from Portugal and the northern coast of New England in the United States northward to subarctic Norway, Russia, and Canada. Salmon are anadromous, whereby they breed in freshwater but migrate to sea to feed. Within their range, adult salmon spawn in cool and well-oxygenated streams. Juveniles spend 1–5 years in freshwater before transforming into silvered smolts. At this stage they migrate to sea, following ocean currents to feeding grounds in the Atlantic. Once in the sea, salmon grow rapidly, feeding on small fish and crustaceans. After 1–3 more years, the fish reach sexual maturity and migrate with great accuracy to their natal rivers, often spawning in the same tributary where they were born. As a result, salmon stocks have evolved into genetically distinct local populations.