There are quite comprehensive databases of Dolphins seen around the UK. They are identified by the nicks, gouges and marks on their dorsal fins; unique as fingerprint. Indeed computer programmes are now available that store and compare fin shapes and outlines. This technique can also be used with Minke Whales and also with Basking Sharks.
We saw this Baking Shark on a pelagic off Mull in June. The photograph will be entered into an index of sightings and its subsequent movements may be tracked if it is seen again.