The Pantanal is one of the largest wetlands on Earth. It is home to a wide range of animals and plants that live by the flood cycle. The main challenge in photographing underwater in the Pantanal is to find a place with reasonable underwater visibility.
Near the end of the wet season I was trying to photograph piranhas at a seasonal river that had formed with the floods. The bait I used attracted many piranhas and other small fish, causing a feeding frenzy. After a few minutes I noticed a caiman approaching to investigate the scene. He tried to grab some fish but at the same time was cautious with me. I took a few a shots and approached some more. It was then he opened the mouth. I took another series of shots. Part of the caiman was almost touching the dome port of the lens. A few times he tried to bite the camera housing, I guess to check what it was. After some time, a second and third caiman came to the scene, I took some pictures but found that it had become harder to track all three animals, especially with harsh shadows and strong lights. In a few minutes I went back to the small boat.
The camera was set to shutter speed priority with the speed at 1/250th (the maximum I could sync with the flash) to try to freeze some of the fast-moving fish. With visibility rarely reaching 6-feet underwater, using a very-wide angle lens is fundamental because less water will stand between the camera and your subject. I prefer the Tokina 10-17mm fisheye because of the ability to zoom in a little bit. With the D2X I tried to avoid bumping the ISO past 800, so I have set the ISO to 400, a good balance between performance and quality for that camera model. Since the sunlight was coming almost from behind, providing some nice sunrays in the water, I used a pair of strobes to fill up the shadows and illuminate the face of the caiman. - Marcelo Krause
Equipment and settings: Nikon D2X camera, Tokina AT-X 107 AF 10-17mm f3.5-4.5 DX fisheye zoom lens, Aquatica D2x housing, Inon Z-240 strobe - 1/250th at f/5.3, ISO 400.
You can find Krause's work at MarceloKrause.com and this image is available here as a print through the Natural History Museum, London. Stay updated on his work by following him at Facebook and Vimeo.