The main writers in Donegal oddly unrepresented (4,3)
I believe the answer is:
open sea
'the main' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for open sea that I've seen before include "body of water away from land" , "Clear ocean" , "The main" , "Unenclosed stretch of water" , "Unenclosed ocean" .)