Because they typically leave when approached, underwater animals can be troublesome and annoying to get photos of. Small wonder, considering people are sometimes huge compared t most animals and an underwater camera-system looks like a big-mouthed, multi-appendage predator. Therefore talented and successful underwater photographers must clearly work awfully tough to get close-ups of reef life.
So how do those underwater photographers get these great shots? It seems that the best tack is no approach. When you come to understand marine-life behavior, you can forecast movements and get impressive close-ups by letting them come to you.
Let's imagine in a dive you come across a sea-turtle scavenging underneath a coral ledge. The turtle is a few meters down the reef and naturally you may spook it if you move closer in, in a direct way. The turtle will turn away straight away and you may finish up chasing it and take another famous "backside of the turtle picture” like you has done many times before.
What you need to do is expecting the trail of the turtle and settle own somewhere there. Just take some time and look at the sea turtle and move as little as practical. Once the turtle realized you're there and you are no threat to it, the turtle will continue hunting and will move closer.
Hold your camera in position and take it slow. You most probably will be well placed to take an entire series of great frontal shots of the sea turtle if you remain calm and still. Your patience will lead to rewards with inspiring footage and a great encounter of this wonderful animal.