I have always thought Sharks would be a good defense mechanism to help ward off intruders and scallywags. But there hasn't been a very clear way for me to see how it could work until now.
You could have some way to acquire/make chum, with unwanted food/fish parcels ect. And chum the water around your ship. This would attract "aggressive sharks" that would feed on anything in the area for an extended amount of time.
