The Abecean Sea is a body of water to the west of Tamriel that sits between Cyrodiil, Hammerfell, Valenwood and Summerset Isle. The sea is encompassed by the Eltheric Ocean.
In Stirk, the Abecean sea separates the island of Stirk from mainland Cyrodiil. In the waters near Stirk lies the shipwreck of the Kintyra II, which you will learn about in The Ballad of Jean and Mori quest and explore during The Lost Delivery quest.