Al
Thanks for the compliments. I shot this with a Canon 5D MK II with a Canon 15mm fisheye in an Aquatica Housing, with the 9.5 Glass Mega Dome and 2 Sea & Sea YS-250's. This was pretty early in the morning so the springs were not getting any direct sun light. I had the ISO set to 400 and the exposures were around F 5.6 at 100-125the shutter. I figured distance and the fisheye would help cover any depth of field issues. A few were shot with out strobes and a few with. I had 8 & 12 inch arms that I had spread out half way with the strobes feathered out even more so that I was only using the edge of the light (the first time I had tons of backscatter) I still had a little bit this time.
You are not permitted to dive down to the Manatee's and it's hard to get down with a thick wet suite and no weights and I did not want all my shots looking like they were shot from the surface. All of my images were shot at arms length away pushing the camera/housing as deep as I could possibly get it then pull the trigger (like shooting from the hip, no view finder), check the LCD for composition re-adjust and shoot again until I got the right composition right.
I hope this helps, I'm going back in a couple weeks and I have a few more ideas that I want to try, I just ran out of time and then a large tour group silted up the area that I was working in.
Mark