Without maps or GPS, great white sharks travel thousand of miles roundtrip from California to Hawaii or Australia to South Africa. Sea turtles hatched on the beaches of Florida travel the currents of the North Atlantic Gyre to Europe, Africa and South America before heading home.
And in one of the most mysterious and epic journeys of all, salmon from the streams and rivers of the Pacific Northwest head to sea and swim into the far reaches of the North Pacific before returning to spawn.
Scientists increasingly believe these marine creatures and others use the earth's magnetic fields to navigate vast distances.
But as the search for green energy turns to the oceans, there are concerns that tidal and wave-powered generators, and the cables that bring their electricity to shore, could interfere with the internal compasses of everything from salmon, sharks and sea turtles to lobsters and crabs.
The fear isn't that the fish and other marine life will get chewed up in revolving turbine blades or other machinery. It's that the generators and the cables to shore produce electro-magnetic fields that could interfere with their natural guidance systems, which use the earth's magnetic fields. In addition, there are some worries the machines may produce a low-level hum that interfere with such marine mammals as whales.
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