Close in, shark perhaps circling (6)
I believe the answer is:
finish
'close' is the definition.
(I know that close can be written as finish)
'in shark perhaps circling' is the wordplay.
'shark perhaps' becomes 'fish' (shark is a kind of fish).
'circling' indicates putting letters inside (circling can mean going around or containing).
'in' placed inside 'fish' is 'FINISH'.
(Other definitions for finish that I've seen before include "Complete or terminate" , "Perfect" , "End, conclusion" , "Patina" , "curtains" .)