Two islands in Abel Tasman National Park will become specially protected areas to protect breeding colonies of fur seals.
The government's announcement means public access to Tonga and Pinnacle Islands will not be allowed without a special permit.
Conservation Minister Maggie Barry said seal breeding was highly sensitive to human intrusion, and there had been problems with people landing on the islands and disturbing them.
Environment Minister and Nelson MP Nick Smith said he wanted the islands to become home to tuatara.