During your return to Gatma Atoll you are faced with a task to locate and heal (with your pulsar) three fish; a Manta Ray, a Humphead Wrasse, and a Manta Whale. These are located at grid marks C3, G2, and E8. If you do not know what you are looking for, the best thing to do is swim to these locations and discover them first. Make sure your tank is upgraded or you will not have enough air to finish the tasks. You will get three tries before you must leave the area and return later to try again.
You will be asked to go to the Blue Cliffs which are located in the deep area of grid marks A and B 8. You must swim around for a bit towards the bottom. Try grid mark B8 and swim towards grid mark A8 first at various depths.
To unlock the Gold Catfish, you must first find the Servants Ring located between the waterfall and elsewhere in Twilight Temple. When you find the Servants Ring, GG will appraise it before you have a chance to call Nancy, and will tell you it is worthless. Next, return to the Amazon where you found the Giant Catfish. A cinematic will play, and at the end you will have a chance to give the fish your ring. Choose "Yes". Do some exploring or something else, then return to the boat. On your next dive, you return to the catfish and another cinematic will reveal that the catfish is now a Gold Catfish.
Have Snorkel on the island and look for him by the bonfire. Pet him to get information about a strange moving island in Gatama Atoll. Investigate that area to find the legendary Leatherback Sea Turtle.]
If you complete at least 25% of the map occasionally there should be an icon above the grid view icon of a magnifying glass with a picture of a fish. Select the icon and the arrows to see nearby fish, or fish you have yet to discover. These will have "???" in the name. After you discover the fish and animal, they will also appear in the encyclopedia after you select its image. This is very helpful when you need to take photos of a fish.
Some fish apparently only appear at night. In Cicero Straits there is a fish that blends in with a shipwreck and it looks like a piece of wood breaking apart from the boat. Use the fish icon on the map to find it.
For the Deep Sea Dive, after you have completed your mission of retrieving the bag from the sub, your portable air tanks will have disappeared. Do not worry. After this is done, you will not need them.
Train your dolphin until it reaches level 2. Meet Finly the dolphin trainer, and have him to see your dolphin show. He will tell you to go to Ciercos Strait to find a white dolphin. Go there and rescue it from the shark.
Photo requests can be found at the following locations:
PHOTO REQUEST - LOCATION Armory Landmark - Unknown. Banded Angel Fish - Deep Hole (A2, small shiny spot). Bertrella Aurantiac - Valka Castle, grid mark C2 at the glowing spot. Capier - All over the Arctic during the day. Cross Rift - Cicero Straits. It should already be marked on your map. You do not have to dive at midnight for this one if you have the Cross Rift dive spot unlocked. Electric Eel - Amazon River, maze forest. Enchanted Hallway - Unknown. Golden Clown Golby - Grid mark F, G, 3, 4, but is found with Yellow Golby fish at the bottom of grid mark G4 (purple coral). Great White Shark - Cicero Straits (E3, swimming above shipwreck). Humphead Wrasse - Gatama Atoll (E8) Manta Ray - Gatama Atoll (C3). Mediterranean Monk Seal - Check your Encyclopedia if you did not take the picture during the rescue mission in Cicero Straits. They are not in the original locations any more. Moon Jellyfish - Cicero Straits (E3, north of shipwreck). Orange Sea Slug - Found where Nancy says it is, on the sand floor (difficult to see), and not in the coral. Tortipsis Nautica (jellyfish) - Valk Castle, Mermaid Ball Room (small shiny spot) Wulruss - Arctic, when you surface through the hole at grid mark A1. The one you are looking for is on the far right.
The secret cave in the Deep Hole area is located in the middle of the Deep Hole itself. You need your dolphin to open it. You must have your dolphin by you and press A when instructed and it will be open.
I have looked all over the twin cave/caverns with Oceana and I cannot find the gravekeeper.
Answer from mightyvader
He DOES NOT appear until the relating "special request" shows in your notebook. When a special request titled "The Grave Keeper" appears in your notebook, THEN return to the twin caves with Oceana to find him.