Team Wetpixel shooting common dolphins, The Sardine Run, Wild Coast, South Africa.
I was really lucky to go to The Sardine Run with Wetpixel team, and I think this was the key to obtaining decent underwater shots.
Wetpixel is leading underwater digital photography and video resource on the internet founded by Eric Cheng, talented and well known new-generation underwater photo-pro. They publish a lot of useful articles on the topic, organize diving trips with focus on photography, maintain very informative and useful forum where enthusiasts of diving and photo exchange ideas and information.
Wetpixel trip was done in different way then most of the more touristy experiences of the event. One of the key aspects I want to describe - we had only five people on the boat - most of operators have something close to ten. Limiting number of people on the boat is very important. Presence of many divers simultaneously in the water affects behavior of predators in the bait ball, sharks usually stop hunting and just hang around if more then two people are in the water. Well, sometimes actually sharks force divers out of water, defending bait ball, this happens two, but not very frequently ;) Presence of big number of people probably also affects behavior of bryde's whales, game fish, e.t.c.
Also smaller number of divers has huge advantage in terms of logistics - bait ball is often moving, and divers need to surface and continue chase by the boat - obviously lifting 3-4 divers out of water is way faster then 10, and bait balls are not waiting - they getting smaller and smaller with every passing minute ;)
In terms of sharks we had good moments in the beginning of bait ball dives, and then we were in the water in groups of two - bringing four people underwater was instantly resulting in sharks going out of bait ball. On other hand dolphins seem to be absolutely unaffected by presence of people, and their numbers were impressive disregarding number of divers in the water.
Needless to say that best pictures done on Sardine Run by Doug Perrine and Thomas Peschak were captured during solo diving - but this is pretty expensive way of doing it, save the fact you need to be super-experienced diver with a lot of knowledge of marine life to pull this - every year some shark accidents happen underwater, mostly involving people not prepared to deal with elevated interest from big predators ;)
Actually production companies like BBC are doing the same solo thing for getting best results for movies like "Deep Blue" ;)