The Marlborough Sounds is off limits to recreational blue cod fishing from 1 October.
A four-year ban has been imposed by the Ministry of Fisheries, although other species may still be caught.
Although some fishermen are still reporting good catches, the ministry says the cod fishery is in serious decline. Juvenile fish have declined by 57% in five years.
The fixed penalty for fishing in a no-take area is $500, although penalties can go up to $20,000 and include forfeiture of boat and equipment.
