From the diving bell swim south into the wreck and avoid the sea urchin and jellyfish as you grab the Treasure and exit out the opposite side into some seaweed. Wait for the shark to turn away and then grab some air at the air barrel before heading into the nearby wreck and getting the next Treasure. Exit out the other side into some seaweed and grab some air.
The hull of the ship nearby has a Treasure straight ahead and if you swim up the trapdoor to the Captain's Cabin you can find another Treasure. Swim on deck and pop in another trapdoor for the Animus Fragment and then grab some air at the nearby barrel. Wait for the shark below to turn left and make a break for the second half of the hull and open the Treasure, ignore the air barrel. Swim left and around to a small set of stairs and swim down the other side to reach another Treasure. Use the air barrel nearby and then wait for the shark to move to grab the Animus Fragment in the nearby wreck.
You will now need to backtrack down the ship, using the air barrel we passed if needed, and make your way to the final Treasure before returning to the diving bell.
