This is one of the few areas without sharks, but you will still need to watch out for other plant and animal life. Start by collecting the Treasure x2 in the area and then use the air barrel to replenish your air before heading into the tunnel behind it. Follow the tunnel until you spot an undersea current and when you enter it you will want to stick to the left wall, using the High Profile Button to swim left at the sea urchin covered stalactite to reach the Animus Fragment. Return to the current and follow it to its end.
Grab some air at the air barrel as you exit the cave and then grab the nearby Treasure, avoiding the eel. Exit the back and enter the next wreck from the deck door and open the Treasure and then follow the tunnel to a current. Head for the air pocket when you reach it and then get the Treasure before you follow the tunnel to an Animus Fragment and another air pocket.
Leave the water and get the Treasure x2, one with the Elite Swivel Gun Design Plan, and then enter the water on the other side to grab the last Treasure. You can now make your way through the tunnels back to the diving bell.
