Shark appearing in harbour (5)
I believe the answer is:
nurse
This clue is a double definition.
'shark' is the first definition.
(nurse shark is a kind of shark)
'harbour' is the second definition.
(I've seen this before)
'appearing in' is the link.
(Other definitions for nurse that I've seen before include "Look after: entertain" , "care worker" , "One tending the sick" , "Hospital carer" , "drink slowly" .)