It's easy to take photos like this. Alexander Semenov explains:
It’s simple: Take a camera and macro lens, and encase it in an underwater housing. Connect all the cords, close it, check all edges and buttons, and check your underwater strobes. Then lug all (approximately) 8kg of your high tech photography equipment out on the boat, dive into the sea, and find your creature. Manually set up all parameters of the camera and strobes—then be sure not to move or even breath—and adjust your camera to find the right focus point (no auto-focusing, all manual). Press the shutter button, and that's it. Well, almost. There are always some environmental issues, such as currents, icy cold water (-2*C), total darkness below 20m depth, constant turbidity, and more. But you can get accustomed to it after about two or three hundreds dives. Good luck!