Hans, I was there last October and took my 24-105, 70-200 f/2.8 and a 100-400, all of which have IS and I had two full frame cameras, one as backup. I found that most of my animal shots were with the 70-200 and most of the landscape panorama shots were with the 24-105. In fact a lot of the beach shots of the iguanas and the Sally Lightfoot Crabs were with the 70-200 and some with the 24-105 at 100mm. I would also suggest that you take a polarizer as a lot of your shots may be across the water and the polarizer will help to cut the glare off the surface. Bring lots of memory cards, or something to download images off your cards on a daily basis, because you will probably shoot twice the number of images that you think you will. I was there for about 8 days on the water and shot over 3000 images. Sunscreen and a good hat are a must. Any other questions, feel free to PM me and I will try and let you know what my experience was.
WesternGuy