Al Shaheen oil field, off the coast of Qatar, is where the whale sharks gather in their hundreds. Scientists are not entirely sure why they choose this spot, but they think it is connected to the large amounts of plankton and fish eggs there in spring. The gathering was first reported widely in 2008 and is still one of the ocean's great mysteries.
A whale shark's mouth can open wide enough to swallow a child whole - but it would never do so, because it feeds by swimming slowly with its huge mouth open and filtering tiny plankton from the water, rather like a whale. Its skin is dotted with white spots arranged in a pattern as unique as a fingerprint.
Qatar has worked with marine scientists to study and protect these visitors. By tagging individual whale sharks with tracking devices, researchers can follow their journeys across thousands of kilometres of ocean. Children in Qatari schools sometimes see drone footage of the gathering, which shows hundreds of whale sharks from above - one of nature's most spectacular sights.