Captains head off to find fish (7)
I believe the answer is:
kippers
'fish' is the definition.
(I've seen this before)
'captains head off' is the wordplay.
'captains' becomes 'skippers' ('skipper' can be a synonym of 'captain').
'head off' means to remove the first letter (the first letter or 'head' is removed).
'skippers' with its initial letter taken off is 'KIPPERS'.
'to find' is the link.
(Other definitions for kippers that I've seen before include "Smoked fish" , "in bed?" , "Smoked herrings for skipper" , "Food for those that have smoked" , "Have they dropped off" .)