Once you have RuneScape gold completed Deep Sea Troubles you can talk to Gompar for another one called Shipwreck. Gompar will inform you a boat has sunk when it crashed in the walls of Mogrin. He will want you to repair the wall. Go up to Captain Murk and let him sail nearer to the wall. He'll do so. You may then dive.
Fix the wall. Go back up to Captain Murk and let him sail a bit further away so that you can dip. He will do that. Proceed to the palace (can be entered through some region) and speak to Gompar.
Inform Gompar you fixed the wall. He will thank you and supply you 16,000 gp. Tell him you believe the boat belonged to a priest that was sailing this way. He will state that he saw a couple human beings swim into a nearby cave at a water cliff but it caved in because of little earthquake. Go in the cave and it will be dry in there because the water can't reach far enough to flood it.
There'll be 3 people sitting down on the cave walls, Captain Lockbard, Drew and Cabin Boy Jeremy. Speak to Captain Lockbard and he'll thank you for discovering him. He'll provide you 3 classic lamps he found in the cave. A cutscene will occur revealing you attracting the 3 individuals up into the ship with the help of this Breathing Orb. Congratulations, quest complete! The benefits are 8,000 prayer XP, 11,000 smithing and mining XP, 9,000 structure XP and the capability to acquire fish summoning pets.
To get fish pets you must have level 73 summoning. Locate fish eggs in underwater caves or someplace, (must have level 73 summoning) if you discover a shark puppy, then you are very lucky. If you take over one egg you can only get one fish. Go to the Fish buy OSRS gold Tamer's room of the palace and he will have a fish egg incubator (you can't incubate any other egg than the fish egg in there.)