While at our anchorage at Motu Toopua, we took our dingy around the tip of the motu next to the outside reef. We were told that we might be able to see some sharks. We snorkeled about for about an hour and saw nothing, until we noticed schools of butterfly fish suddenly appearing, seemingly from nowhere. A party boat full of tourists pulled along side of our dingy, and we were immediatelly surrounded by Black Tipped Reef Sharks. The fish in this area were obviously used to being fed by this boat and knew the sound of it's engines.