The reason I love digital is because you can take pics of everything under the sun or water in this case. Since you don't have to worry about how they turn out take all you can.
However, on my dives, I don't take pics every minute or so. I will take a group of pics and then let the camera auto off go to work. Many times there are plenty of things to photograph but just how many pics of the same animal can you have.
Take the pics, as many as you want but when you don't see anything to shoot, turn it off. I don't think you use any more power turning it on and off. To me, if you are just diving and having the camera on all the time, that is a waste of power.
Like I said, I get atleast two dives and have plenty of power after that.
Have a great day and send some pics.......