Two things to remember when going out on a boat on the sea:
1. Even if going scuba diving, take a camera for above water in case there's a species of petrel that you will never see again flying about when you finish the dive. Forgetting this is why I have no photo of Barau's Petrel.
2. Don't assume that birds will be the only thing to photograph and so think you just need a powerful lens. There might also be dolphins bow-riding, and to photograph them you need a fairly wide angle lens.
8562 Whiskered Auklet. If you reflect the location of South Georgia across the whole of the Americas you get to the Aleutian Islands and a bird which is probably an example of parallel evolution with the diving-petrel.