I think you don't really need a zoom underwater, water should be very green and full of plankton at that time, you can't get a clear photo if they are not close enough.
Two cameras may be a good idea, there were quite a lot of seals for you to shoot in the boat and the scenery was gorgeous.
Will you also go to Lunga Island for birds such as puffins? The island was really lovely.
- A.A.Ron likes this