From the bell at the start of the dive, swim to the southwest and into the upturned ship hull. Inside you’ll find a chest. Continue out the far side of the wreck and immediately turn to the left to see another, larger wreck in front of you. Watch out for the eel and sharks as you swim the short distance over to the entrance. Go inside and grab the chest on the floor in here. Use the air barrel just outside if you require it.
Now swim directly south until you find another air barrel. Ignore this for now and enter the shipwreck behind it and avoid the pair of Moray Eels for an Animus Fragment. Return and use the air barrel.
From here, swim up to the large wreck perched on the rock shelf above us. Swim over the railing and look for a chest in the corner near the base of the first mast. Keep following the deck of the ship to the north until you find the next air barrel.
After this; dive straight down into the gap between the two halves of the ship and look beneath the debris on the seafloor for another chest. Continue along the sea bed to the north until you reach another air barrel.
After using the air barrel, swim up to the northern half of the ship and enter the open door in the hull. Dodge the spiky sea urchins on the pillars inside and swim through the hull. When you reach the corner, grab the chest directly in front of you, then turn and follow the passage all the way back to find another chest. Now follow the passage all the way east and up the ramp at the end. Open the chest at the top.
Now quickly turn around and swim through the opening ahead to find an air barrel. Finally, swim to the second platform near the top of the still in-tact mast to find the final Animus Fragment. Lastly, make your way all the way back to the diving bell. Interact with this to return to the Jackdaw.