Assassin's Creed 4: Black Flag Walkthrough Part 81 Shipwrecks & Caves: “La Conception”
From the Diving Bell you need to swim down to the sea bottom and make for the patch of seaweed there. Now look for the Jellyfish that are in front of you. Swim through them carefully to get into the first part of the wreckage to claim the first chest. Go through the other opening and duck into the nearby seaweed patch. From there make your way carefully over the air barrel that sits nearby. Refill your breath then duck into the seaweed. Wait for the sharks to be moving away then use the nearby burst beam to make it over to the next part of the wreckage. Navigate around the jellyfish and claim the second chest.
Turn to the Southeast and make your way toward the next air barrel in that direction. Do so carefully around the sharks that are patrolling the area you are in. Now go to the Northeast and into the wreckage of the ship itself. Go straight until you reach a wall. Go just to the right of it and up to find the next chest. Look below that wall to the right. There you will find an Animus Fragment. Make for the deck of the ship then go to the captain's quarters entrance to get the next chest.
On the deck make your way up the nearby mast toward the Animus Fragment. Now make for the next nearby air barrel. Just by it you will find the final Animus Fragment for this area. Now go over to the final part of the wreck. Just inside it, to the left of the air barrel, is a chest. This gives you the design plans for the Elite Ram. Grab it then press on toward the deck of the ship. Once on the deck you need to be careful of the sharks. Head toward the Southwestern portion of this ships deck. Use the mast to keep the shark's line of sight off you. Grab the chest there then turn to the North and swim into the ship wreckage. Go through the door and turn left. There you will find the final chest. Grab it then you can return to the Diving Bell triumphant. It is a quick swim.