Thanks for the tips Core. Antoine Berry in one of the videos above does not recommend shooting the shark in the head. I believe a stone shot is very unlikely and he says that the shark goes crazy and becomes dangerous when shot in the head. On the other hand shooting the shark towards the rear will tire it out putting the diver at less risk. At least that's the theory and I wanted to know what you thought about it.
In Cuba subsistence spearfishers will kill nurse sharks for food when they can find them. I know the feeling when you see nothing all day and finally you have this big beast in front of you. However I tried nurse shark meat and didn't like it. Since then every time I saw the cuban spearfishers carrying one I thought "abusadores". But you have to see it from their POV also, none of that fish goes to waste. And they do risk their precious shafts and guns to get it when they don't have a powerhead.