The day brought 4 lifers:
Humpback whales : fluke patterns :: humans : fingerprints
Every individual humpback whale has a unique pattern on it's fluke, and naturalists photograph and catalog the patterns. Then they can record sightings of individual whales and track their movements to some extent. After years of studying the whales, naturalists and marine biologists can easily recognize a whale's distinct fluke pattern--that's how we knew which whales we were seeing, thanks to our on-board naturalist, that is. Apparently the dorsal fin of a humpback whale is also a good identification tool for individuals.
Here are some more pictures from the day's trip:
Take nothing but pictures (and maybe the trash of jerks who came before you), leave nothing but footprints.