My swimming skills are being put to the test as Hillary, Thanda Island's whale shark expert, heaves me by the wrist through the water off the coast of Tanzania in pursuit of a specimen that is supposedly lurking in the depths. My flippers are thrashing and I'm forgetting the basic principles of a snorkel - surely this can't be worth the struggle. One final push and there it is: a huge, elliptical mouth heading straight towards me, attached to eight metres of whale shark. It changes course at the last second, flecks of its speckled skin gliding past centimetres front my fingertips, before a last flick of its tail as it vanishes down into the blue abyss.
“I forgot to say, Hillary doesn't speak English, so if he grabs your wrist, just go with
