I jumped in the water off the diving platform on the transom, fired off a test shot (the greater shearwater from below - also included is a greater shearwater shot from above. shots taken on separate days) and started swimming as fast as I could toward the shark.
You can see from the shearwater "from below" shot, the water is beautiful. It's was ~400 feet deep, too. When you're looking down or in any direction other than up, it's all blue... unless you're within 20 or so feet of something. This meant as I swam toward the ~25' shark, I was surrounded by immense blue and I wouldn't see anything in the water until I was right there next to it. My heartrate was flying.
I was pretty far from the shark when I got in the water and was working hard to catch up. My thoughts were split between, "I hope I can get a shot" and "I hope I don't stumble upon this massive creature in the middle of the Gulf of Maine... to realize I mis-identified the species..."
The folks on deck were kind enough to sing the JAWS theme when the basking shark went below the surface for a bit. Thanks guys.
After a serious effort in the water, everyone on deck informed me that after I reached a certain point, the shark was swimming away from me just as quickly as I was approaching, and we had stations to finish. So, no underwater shot of a basking shark, this time. But Cameron got a nice shot from the deck of me swimming toward the shark, camera in tow, with a nice sized fin in the background.
Too add some size perspective, I've also included two shots of the shark shot from the deck before I jumped in. It was too big to fit in the frame of just one shot. In the first, you can make out the pectoral fin: the white markings below the surface. The nose and body of the shark are detectable by the subtle change in color from the water.
The second shot is easier to make out: The dorsal fin on the left, and the caudal fin just below the surface, stirring the water on the right.
Swimming with the basking shark (above).
Dorsal and caudal fins seen from the boat (below).
Enjoy. I'll put up more pictures of other cruise adventures over the next week.