um......
firstly too many sharks are dying needless deaths at the hands of commercial industry for sharkfin soup in the pacific islands. those few (I hope) fisherman who paranoiacly protect their precious catch engage in negative killing out of pride and bravado.
in the Marianas, spearfishermen contribute to the marine taxman (agressive sharks) without question. sometimes bull shark dont get enough, and start arching for more, and you know it is time to leave, much like a disgruntled trucker at a bar who breaks a bottle in your honor. I dont believe in ever needing a powerhead because you shouldnt dive openwater alone, or without a boat nearby to exit the water.
I dont believe you should have to kill any shark unless your immediate life were in danger, I.E. 12-16ft tiger starts niping you even after you have jabbed him a few times, and given him all your fish, and your buddies poking isnt changing his mind, and you are prevented from exiting the water by said predator, in that rare circumstance the choice is up to you.
the rest of this poll is foolish speculation for someone new to the ocean world, and the predator prey dynamic.
sharks are like wild dogs, dont act like an easy prey and they will leave you be, respect them and most will respect you, after all, every time you plunge, you are in their world as a visitor, act like it. if in a large pack, even friendlies, you might consider leaving before they engage in group activities that are unsettling to your pallet.
and keep in mind the difference between hunting and Murdering, I hunt with humility and gratitude for food, to either feed the self and or a family, the rest is unnessary recreation, and dispaching any non prey fish; (sharks, or any sea mammal, and Turtles, stingrays, ect.) is murder in my book.
Like a shark, I stop when I have enough to feed me, and come back when I am hungry, it is still recreation, but with a higher purpose. and the permanent fishermen (sharks), AKA the Taxman, will sense this about you and give you some latitude.
thanks,
TBG