Fish traps at sea (5)
I believe the answer is:
sprat
'fish' is the definition.
(sprat is a kind of fish)
'traps at sea' is the wordplay.
'at sea' indicates anagramming the letters.
'traps' is an anagram of 'SPRAT'.
(Other definitions for sprat that I've seen before include "Type of herring - small person or thing" , "Small herring-like fish" , "Small edible fish" , "Small marine fish" , "chap giving richer course material to the Dutch" .)