Shooting a series or sequence of pictures of the subject you have selected is a great way to increase the chance of a successful and nicely framed picture. Because it offers you the possibility to pick out the best picture of the series later on yout laptop, as a 'keeper'. One type of sequence I often use with fast moving subjects like sharks is the approach sequence.  It is the same technique used by photographers to catch that unique moment of making a goal in a soccer game. These guys however are equipped with a tele lense and use high shutter speeds, because their subjects are much further away from their target and are moving  pretty fast. 

You notice that a shark is moving towards you, but instead of waiting until it is close enough you start 'clicking'  when it is still some meters away.  You will not need a super fast shutter speed, but only  keep a close eye on the shark thats moving in. Say you select:  1/125, ISO 200 and @11 with enough sunshine. You can adjust the  focus  stepwise with the thumb button when the shark approaches. Often, when the shark gets pretty close to your dome, it will swiftly turn away from you.  That will be the 'golden moment' and the resulting picture probably  the  one  you want to keep. But sometimes you are not that lucky, and the shark may decide to turn away from you at an earlier stage. With a fish eye lense and its immense depth of field a picture of the shark at a more remote position will still often still allow a  nice and sharp crop of your subject. See the example below of a seven  shots sequence of an Oceanic shark moving in. The 7th shot looked fine enough  to keep for my album.