Trace fishing vessel (5)
I believe the answer is:
smack
I believe this clue is a double definition.
'trace' is the first definition.
(thesaurus)
'fishing vessel' is the second definition.
(I've seen this before)
(Other definitions for smack that I've seen before include "box" , "Fishing-boat, hit" , "Hit - drug" , "Suggestion" , "Slap the fishing vessel" .)