Hi All,
It depends on the animal in question I guess. I once spent almost seven months making a short film on Mandarin fish. I got all of their nightly behavior but it just took determination and time to sit there night after night to get the shots needed, the final piece was just 15 minutes in length, and long at that. For that project I hardly got any decent footage in the first month as the fish were incredibly skittish when I used the video lights (25w Osram Bulbs). It took a month of me repeatedly going back to the same coral head before they were comfortable enough with my presence to pretty much ignore me and get on with their business. When I started documenting their behavior I then noticed that so long as I stayed pretty still they would swim around me. If I tried moving around them they would take cover almost immediately. Hence the seven months for completion.
For other animals, larger beasts such as Sharks and Mantas of which I have dived with extensively over the past almost seven years of being based in Yap, Micronesia and Palau, all I can say is breathing and stealth.
Mantas:
Our interaction with them is normally at times when they are feeding or cleaning, and if very lucky during their mating season. When they are at cleaning stations their comfort zone should be respected at all times. If a manta approaches me at any given time I hold my ground and stay as low as I can get. I don't make any sudden or erratic moves, fluidity is the key. If they continue and fly directly over me I, against safe diving practice guidelines
attempt to hold my breath. I do this to avoid the larger exhaust bubbles from hitting their bellies and scaring them. Seeing as I've deflated my BCD there is no danger from ascents due to full lungs etc. For those wishing to maintain an open airway, try breathing out through your nose. This will avoid large exhaust bubbles as your exhaled air will escape from the skirts of your mask.
Moving around a cleaning station is a sure fire way to scare the animals off. If you must move do so at times when the manta has its back to you. You will see by observing them at the station that they stick to a pretty standard flight path, for want of a better term. Move slowly, deliberately and low when they have their back to you and stop before they start any head on approaches again. Repeat until you are in your required position. It really bugs me to see camera wielding divers swimming like buggery after a manta trying to get their shots. It achieves nothing and really freaks the animal out.
If you are fortunate enough to witness multiple mantas during a mating season or feeding behavior just stay low, avoid blocking their flight paths and hope they are in the mood to 'perform' for you. In three years of diving almost everyday with mantas in Yap I have about 4 hours of multiple manta footage in clear water and about 1 minute accumulative footage from three attempted mating actions. Rare stuff.
Sharks:
I can only offer input based on the interaction with species here in Palau on a regular basis. Grey Reef, White Tip Reef, Black Tip Reef, Zebra and Nurse. The only thing I can say for free swimming species is to maintain a very slow approach at all times. Breathing is also key, spend a minute or two getting close to a patrolling Grey Reef Shark and then letting out a plume of bubbles once in position will normally result in the shark readjusting its flight path. I often mention to snappers here that the best approach is to use your exhalation as a way to gauge how close they want the sharks to be for any given image.
For any species who may, at times, be encountered laying on the channel bottoms or in sandy areas etc, it's all in the approach. Stay calm, breath slowly and low and move meticulously and deliberately.
Apart from that if you are given the opportunity to witness and document any particular behavior such as hunting, cleaning or mating then make sure to avoid crowding the animal. This could lead to the animal either having to interrupt its natural course of behavior or lead to you gaining another bodily orifice!! Not what the doctor ordered.
Like I said, this is from what I have seen and learned from interacting with sharks in Palau and Yap. For other species I'm sure there are other people out there diving with them sufficiently in order to supply the relevant information.
Cheers,
Mark.