Traps mackerel-catcher (5)
I believe the answer is:
sprat
'mackerel-catcher' is the definition.
I can't judge whether this definition defines the answer.
'traps' is the wordplay.
'traps' anagrams to 'SPRAT'.
Though, I am unsure how this is indicated.
Can you help me to learn more?
(Other definitions for sprat that I've seen before include "Small sea fish" , "chap on a fat-free diet" , "Type of herring - small person or thing" , "Strap up the small fish" , "Jack, perhaps" .)