Composer docked pleasant vessel from South Island (7)
I believe the answer is:
puccini
'composer' is the definition.
(Giacomo Puccini)
'docked pleasant vessel from south island' is the wordplay.
'docked' means to remove the last letter (to dock can mean to remove the tail of an animal).
'pleasant' becomes 'nice' ('nice' is associated in meaning with 'pleasant').
'vessel' becomes 'cup' (I've seen this in other clues**).
'from south' is a reversal indicator.
'island' becomes 'i'.
'nice' with its last letter removed is 'nic'.
'nic'+'cup'='niccup'
'niccup' in reverse letter order is 'puccin'.
'puccin'+'i'='PUCCINI'
(Other definitions for puccini that I've seen before include "Italian operatic composer" , "Madame Butterfly composer" , "Opera producer" , "Composer of 'Madam Butterfly' and 'La Boheme'" , "Italian composer of opera 'La Boheme'" .)