Imagine yourself swimming in the Sargasso Sea in the Atlantic. The color blue dominates this part of the world – there’s nothing to see but a vast expanse of water and sky in all directions. The winds are calm. The water is warm, clear and deep. You have a destination in mind, but how do you choose your direction, and maintain it, day and night, for thousands of miles? Without a compass or GPS for guidance, this would be an impossible task for a human being. Yet many marine animals routinely achieve this feat during their yearly migrations between breeding and feeding habitats.
Sea turtles are known for their spectacular long-distance migrations. After many years at sea, they can pinpoint their natal nesting beaches after crossing entire ocean basins. We don’t know the distance covered during their developmental journeys but this period can last several decades, and they likely cover tens of thousands of miles. The largest, fastest and deepest-diving species of sea turtle is the leatherback (Dermochelys coriacea). Leatherback sea turtles can grow to over a thousand pounds on a diet of watery jellyfish. They travel extensively between tropical and temperate habitats to gorge on seasonally abundant gelatinous prey. It’s a mystery how they maintain their headings to travel direct migratory paths over such vast distances.