Thanks guys! I did use a strobe on this shot. It's mounted off camera on a bracket. I'm still learning the dive photo stuff. When you use the strobe underwater you get a lot of back scatter from the floating stuff and have to spend time cleaning it up in post.
I think it was about 20 feet. It was at a shark feed, frozen bait ball that they were all going after. I took so many I can't remember the distances on them. I did crop the shot down in post.