Yukon River chinook salmon boast the longest freshwater migration in North America, traveling more than 3,000 kilometers (nearly 2,000 miles) from their spawning grounds in Canada to the mouth of the Bering Sea in Alaska. A smolt preparing to enter the ocean is small enough to lay across the palm of your hand. But by the time it returns four or five years later to swim back upriver, it will be about a meter long (more than 3 feet), and weigh 14 kilograms (more than 30 pounds). Not all Pacific salmon (Oncorhynchus spp.) travel as far, or grow as big, as the Yukon River chinook (O. tshawytscha), but they all make the journey from freshwater spawning grounds to the ocean, then return to their natal streams to spawn and then die en masse. Those remarkable journeys connect and nurture distant ecosystems. That’s because salmon gain most of their body mass in the ocean, and when spawning adults travel back inland to die, they ferry energy and nutrients from marine to terrestrial ecosystems. Those migrating salmon are eaten by bears, eagles and a slew of other predators. Scavengers devour carcasses left rotting in streambeds, or discarded in the forest along streams by other carnivores. Ultimately the nutrients diffuse throughout the ecosystem. The young return to the sea to reinvigorate the cycle, in a dance that has lasted unknown centuries — until modern humans began interfering. Today, researchers can trace the pathway of these nutrients using the “salmon signature,” an isotope of…This article was originally published on Mongabay
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