Maintain seafood around island (5)
I believe the answer is:
claim
'maintain' is the definition.
(I've seen this before)
'seafood around island' is the wordplay.
'seafood' becomes 'clam' (clam is a kind of seafood).
'around' is an insertion indicator.
'island' becomes 'i' (geographical abbreviation).
'clam' going around 'i' is 'CLAIM'.
(Other definitions for claim that I've seen before include "Take" , "Assertion of ownership etc" , "Assertion; demand" , "title" , "Allege" .)