I just thought of something that was just mentioned in the Fishing kit thread that's currently running very parallel to this one. In a survival situation, you don't want to expend energy if you don't have to.

Hunting/fishing with a spear/harpoon seems like an aweful lot of energy expended for a potential of zero gain. I guess if you lived in the right area it might be a workable backup but the more I think about it, the less I can imagine ever catching a fish in the waters around here with any kind of harpoon.