Yeah, hard as it would be, I wouldn't interfere... on principle (the shark's doing what a shark's gotta do!); and because it would mean killing the shark; and because I wouldn't want to, um, piss the shark off and give him any other ideas.
I disagree with Kim, though... I definitely will try to rescue a bird or a mouse from one of our cats if the cat ever got outside!! (Indoor kitties, but they definitely understand hunting... how do they catch birds so well?)
There's another side to that coin, though, underwater... a lot of times when night diving, you can attract a predator toward a potential prey by shining your light on the prey. Like, lionfish immediately come over to investigate whatever you're shining your light on. I think you've got an obligation to "protect" that potential prey for a bit after you're done looking at it... no?
--Marek