Fish rare in sea area separating Ireland and Scotland
I believe the answer is:
marlin
'fish' is the definition.
(type of fish)
'rare in sea area separating ireland and scotland' is the wordplay.
I cannot really see how this works, but
'rare' could be 'r' (listed by Oxford Dictionary of Abbreviations) and 'r' is found in the answer.
'in' is present in the answer.
'area' could be 'a' (maths abbreviation) and 'a' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for marlin that I've seen before include "Spearfish" , "Sea roamer" , "type of fish" , "Large ocean fish" , "Large sea-fish" .)