Imagine eating nothing but jelly all your life. It’s hardly the richest source of food, and you might expect an animal with such a menu to be small and feeble.  You’d be wrong. The leatherback turtle eats jellyfish and little else, but it grows up to 640 kilograms in weight, and can migrate over thousands of kilometres. How can such a powerful giant subsist on such ethereal meals?

This is not an easy question to answer. Leatherbacks feed well below the ocean surface, and the jellyfish they seek are found in dense but sparse patches. Finding the animals, and studying their eating habits, is very challenging. Mike James from Dalhousie University, Canada, did it by attaching small video cameras