Researchers studied the animals, one of the world's most endangered species of dolphin, for 21 years.
Their results show that the survival rate of the dolphins has increased by 5.4% since the Marine Protection Area (MPA) was declared.
The findings are published in the Journal of Applied Ecology.
"This is the first evidence that Marine Protected Areas can be effective for marine mammals. We found a significant improvement in the survival rate," said Dr Liz Slooten from the University of Otago who undertook the research.
In 1988 the Banks Peninsula Marine Mammal Sanctuary was established in the hope that resident dolphins would be protected from fatalities associated with the gillnet and trawling activities of the fishing industry....
