A buddy of mine had a video of a black bear hunt with a spear that I made the mistake of watching. The way they did it in the video was from a tree stand and they would wait until the animal was directly below so they could drop the spear directly on the spine. It was deffinately NOT a quick humane kill.
I also know that there are certain spear hunting videos that peta uses to turn non hunters into anti hunters.

"Nocked,cocked & ready to rock"