Think for a minute about some of the coolest underwater photos you've ever seen, and the odds are good that you'll find yourself reminiscing about photos that involve marine life interacting with their mates, interacting with the environment, stalking their prey, or engaging in some other incredible behavior. While it's easy to see marine life behavior while diving, it can be a little harder to capture that behavior for posterity. Here are some tips to make it easier.
Equipment Matters
While you can get photos of marine life behavior with a simple point and shoot, using special equipment including the right kind of lenses makes a major difference in the quality of the photos you'll be able to take. Those amazing action shots you've admired in the past were probably taken with a dSLR camera and a fast prime lens instead of a zoom lens. If you have a compact camera, you will probably have to try harder to focus on fast moving marine life.
Try to match the lens to the animals you want to photograph; for example, use a 60mm or wider lens for larger fish and zoom in as much as you can. Macro lenses behind a dome port work well for these animals too. Use a 100mm or longer lens to capture skittish, fast, or small marine life; add a 1.4x teleconverter to extend the range of your lens if you like. If you're using a compact camera on small, fast, or skittish fish, zoom all the way out to get the best shot possible. If the animals you're photographing are large and don't move much, try photographing them with a wide angle lens.
Watch for Behaviors
Knowing how a fish or other marine animal behaves is essential to getting the best action shots possible. Where are the fish found? What behaviors do they engage in? What time of day are they most active? What is the best way to approach them? If you don't know the answers to these questions, ask someone who does, or spend some time researching. There is plenty of marine life information available - putting it to good use will enable you to capture the shots you want to.
Once you get close enough to see the fish or other animals you plan to photograph, watch them for behaviors. Usually, behaviors are repetitive - fish will yawn, fan the substrate with their fins, bump other fish, nibble at corals, and chase one another. If you're lucky enough to capture predator and prey, or happen upon marine life mating, don't wait for the perfect shot. Instead, fire away, and keep your fingers crossed. The more photos you take, the better your chances of coming up with one or two "keepers."
Check your camera's settings before you get to the dive site. Make sure your camera is set to the proper aperture and shutter speed - some good settings to try are F8, 1 / 125th on a dSLR camera or F5.6, 1/200th on a compact camera. In addition, put your camera on the fastest focus mode so it shoots instantly when you press the shutter.
Do a test shot on a stationary object to ensure the background colors are acceptable, and position your strobes before you come in close to the fish or other marine life you intend to photograph, then move into position slowly and deliberately, giving your quarry time to get used to you. Keep your movement slow and easy so you don't scare your subjects away.
Photographing marine life behavior can be a challenge, but it's ultimately very rewarding. Keep practicing and don't give up - the more photos you take, the better your chances of getting the perfect shot.