One night, when we were in Mopelia, we had no wind and thus dead calm water. The water clarity was high and with not a ripple in the water it was if the sharks circling our boat were swimming in air. In fact, the only way I knew the sharks were below water is because there were no ripples. When their fins would occasionally break the surface they would leave a wake.
We came out on deck with a glass of red wine and spent an hour watching them. We don’t know why they circle the boat. When we drop anchor in an atoll we fairly regularly get a colony of small fish eating at the crap growing on the bottom of our boat. Often, we have a bunch of remora who hang out hoping we’ll throw our compost overboard. With the remora often come a few small black tipped sharks who include us in their back and forth search pattern. They come to the boat if there is a splash but once they see that the splash is us swimming, they turn away.
Here is a series of photos taken that evening of the black tips and one of a remora. I snuck one in of a shark with our kayak, and a shark with fin breaking the surface for perspective. All pictures taken from the deck of our boat (i.e., out of water!).