Leave Ziara Altanin and head through the village once more, onto the docks. On the eastern side of the docks there is a long ship. Jump over the eastern side of the ship and you will land almost on top of the Abyssal Marker. Interact with this to gain a swim speed buff (you will need it!). Now follow your map marker to a location far to the south in the middle of the ocean. Fathomlord Budlopudlul will be lurking in the depths of the ocean. Slay him to complete your quest objectives. This quest will be turned into Alys White at the Trawling Post. With your swim speed but still on head to the northeast. Your map beacon should take your straight to Alys where you can speak with her to finish the quest.