Head for the first Treasure using the burst beam to plunge forward, while avoiding the shark, and then head across the deck and enter the other side of the ship to reach the air barrel. From the air barrel look down the ship and wait for the shark to clear the path and then make a break for the next Treasure. Enter the nearby doorway and turn left to go up some stairs back to the deck and get the Treasure behind the wall here while avoiding the shark. Wait for the shark to turn again and head over the left side of the ship, over the stairs and along the side, and enter the hull again.
Swim to the right to get the Animus Fragment and then down to another Treasure before leaving to some seaweed on the sea floor. By now you will be starving for oxygen, so make your way to the air barrel nearby before you drown. Backtrack a bit to a Treasure guarded by eels and then head east. Use the seaweed and burst beam to head east and then turn north and avoided two more eels to get another Treasure with the Elite Broadside Cannons Design Plan. Head south now, avoiding the shark once again, and make your way to the air barrel.
The Animus Fragment above you is out in the open and will likely get you bitten by a shark as you head for it, but no worries. Once gotten, make your way back down to the sea floor and head along the seaweed to the next air barrel and the final Treasure. From here you should have no problem reaching the Animus Fragment at the bottom of the final ship. You can now return to the diving bell.
