Its a very interesting thing to see how different animals are subjected to different moral treatment based on cultural norms.
I keep snakes. I breed rats. I feed rats to the snakes. It doesn't bother me and never will. The rats (both breeders and feeders) get treated very well and are kept in humane conditions. Your are what you eat and your snakes are only as happy/healthy as the prey they feed on.
Now, if I were to imagine my cat being fed to a burmese python, I'd probably be sick.
I try to keep a consistent moral belief and in all honesty, if someone chose to use cats as food for snakes (I know it was a joke but just for discussion purposes) and treated the feeders in a humane way, I don't think I could have any major objections other than just the fact that I didn't like it because I like cats.
It just bothers me when people pick and choose when they want to object to without any form of consistency in their beliefs.
In any event, I think that the use of live mammals for shark bait is not a humane practice given the special circumstances of the situation. While feeding a live rat to a snake in a dry enclosure is acceptable to me, dragging a live mammal through the water on a hook is NOT humane treatment. In the case of humane treatment of live feeders, I believe the means are just as important as the end.