It's mostly off-shore (2,3,4)
I believe the answer is:
in the main
This clue might be a double definition.
'it's mostly' is the first definition.
(I've seen this before)
'off-shore' is the second definition.
Both the definition and answer are adverbs. Maybe there's an association between them I don't understand?
Can you help me to learn more?
(Other definitions for in the main that I've seen before include "Where schools are found" , "On the whole" , "seaborne?" , "Generally - at sea?" , "Primarily" .)