For early attempts with a fisheye, these shots are great – nicely framed and evenly lit. They are also very well conceived, using the harsher light of the sun to back-light the foreground subject.
So, constructive criticism... Those foregrounds are a bit drab. It looks like you were in the Caribbean or the Bahamas, where this type of coral is quite common. When it's lit with strobes, it comes out brown, which is nice, but not spectacular. Try looking with your torch for bright sponges in reds and pinks and oranges, which will provide a more dramatic counterpoint to the blue water background. You just need to apply your close-focus, wide angle technique to a more striking subject.
The second image has less impact, perhaps because the foreground is a bit empty. It would probably be better if you cropped in close on the coral tree and left out the bottom third of the image.
Other than that, it's just a question of working closely with your model: get them to tie down that stray cylinder strap, stow that dangling torch away, then experiment with as many different poses as possible. If the model is your buddy, discuss a few different modelling 'moves' before the dive so that you can communicate them as easily as possible underwater.
Edited by Simon Rogerson, 07 January 2010 - 03:46 AM.