Whale is a major catch for some (4)
I believe the answer is:
orca
'whale' is the definition.
(orca is a kind of whale)
'major catch for some' is the wordplay.
'some' says the answer is hidden in the clue.
'ORCA' is hidden within 'major catch for'.
'is a' is the link.
(Other definitions for orca that I've seen before include "Killer at sea" , "Sea creature" , "Massive killer" , "ship" , "Danger for swimmers" .)