Female leaves old seafood in the Channel Islands (5)
I believe the answer is:
ormer
'seafood in the channel islands' is the definition.
(seafood found on the Channel Islands)
'female leaves old' is the wordplay.
'female' becomes 'f' (abbreviation).
'leaves' indicates named letters should be taken away.
'old' becomes 'former' (I've seen this before).
'former' with 'f' taken away is 'ORMER'.
(Other definitions for ormer that I've seen before include "Ear-shaped shell" , "sea creature" , "seashell" , "Ear-shell" , "Delicacy from Channel Islands" .)