Items need for this:
1. A spear (ya that's basically it... pretty simple)
Next, you will need to do something that can get you killed if you don't do it correctly. You will want to jump into the water and wait for the shark to swim towards you. Wait for it to get close enough that it will go under or next to the ramp and starting stabbing it with the spear. Since the shark turns kinda slow, you will get about 1-3 hits on it, if you could. From now on, just repeat this sequence until the shark is killed, then harvest your food, and continue making your base without having to worry about the sharking attacking. I don't know the exact respawn time for the shark, so make sure to keep your eyes peeled in case it spawns back.