South Island's diving aid (5)

I believe the answer is:

scuba

'diving aid' is the definition.
(as in scuba diving)

'south island's' is the wordplay.
'south' becomes 'S' (abbreviation).
'island' becomes 'Cuba' (Cuba is an example).
's'+'cuba'='SCUBA'

(Other definitions for scuba that I've seen before include "breather" , "Skin-diving apparatus" , "Sort of diver" , "Apparatus for divers" , "Diving equipment" .)

I've seen this clue in The Times.

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