While it is possible to take a bear out with only one shot, that shot isnâ€™t going to come from a pirate. Muskets aren’t know for precision or long range sniping. By the time the pirate has discovered this, the bear will already be eating a pirate face hamburger. Or spitting out the pirateâ€™s face because damn, pirates is nasty.
A ninja could land a dart in a bearâ€™s eye, but not with enough penetration to lay it out. Doing this would only piss the bear off. Ninja would then be forced to retreat up a tree, sensibly.
Bears can climb, of course, but doing so gives the ninja enough time to load up some poisoned darts and stick them in the bear as well.
Whether or not a few darts or shuriken would dose enough poison to actually down a bear remains to be seen. Regardless, the bear wouldnâ€™t be feeling so great, you know, bit woozy, definitely not in the mood to play monkey, and would thus leave the ninja alone and go back to eating the pirate. After finding some mustard or something to hide the taste.