you have to wear the grass skirt
The medicine man makes you a potion in a coconut. Shoot it at the shark and it will fall asleep. Swim to the island on the right.
The mission on Shark Tooth Island is to rescue the boy who is stranded in an island in Booga Bay (far right of the island) by the giant shark Booga. The solution is to gather the ingredients for a sleeping potion, to be mixed by the island's medicine man. (see related question)
You have to gather three ingredients and mix them into a sleeping potion. There is a medicine man who will mix them for you, and you can feed it to the shark in a coconut. (see the related question)
Find the three ingredients for a sleeping potion, and have the medicine man mix it and put it in a coconut. Feed it to the shark. (see related question)
At the completion of Shark Tooth Island, you rescue both Professor Hammerhead and the missing boy, both trapped by the menacing giant shark. The "calming potion" (knockout drug) created by the medicine man puts the shark to sleep and you can swim out to the island. (see related question)
When you have collected the three ingredients (and the grass skirt) the Medicine Man will mix them into a coconut for you. Use the giant coconut cannon at the beach, and the shark will swallow the potion and fall asleep.
Shark Tooth Island
Someone has built a "coconut cannon" to feed the giant shark. Get the medicine man to mix the three ingredients into a coconut. (see related question)
The sleeping potion for the shark requires three ingredients (coconut milk, bone, key ingredient). Find them and take them to the medicine man (in the "tree" next to the ruins), who will mix them into a coconut for you to feed to the shark. (see related question)
Once you collect the ingredients for the sleeping potion, the medicine man mixes them into a sleeping potion for the shark. Once he is asleep, swim out to the island in the bay, where you will find the missing boy, and Professor Hammerhead as well. Lead them back to the beach.
You use the cannon
I'm not sure, but it might be some potion or incense