(CNN) -- Coastal areas that ban fishing can provide havens for endangered wildlife, according to a new report.
Findings from a research project conducted over 21 years and published in the "Journal of Applied Ecology" revealed that a marine sanctuary off the coast of Christchurch, New Zealand has significantly improved the survival of Hector's dolphins .
They are one of the rarest species of dolphins, endemic to the waters around New Zealand, with only around 8,000 animals thought to be left in the wild.
Marine Protected Areas (MPA) have long been advocated as a way to protect sea mammals, but the New Zealand project is the first to confirm this.
"This study provides the first empirical evidence that Marine Protected Areas are effective in protecting threatened marine mammals," said Liz Slooten of the University of Otago.
Since the MPA was designated, the dolphin's survival has increased by 5.4%, according to the report.
Covering 1,170 km2 of sea off New Zealand's South Island, Banks Peninsula Marine Mammal Sanctuary was designated in 1988 to prevent the dolphins being killed by gillnet and trawl fisheries.
Between 1986 and 2006, researchers conducted regular photo-identification surveys of Hector's dolphins, photographing 462 individual animals whose survival they studied.
"We can identify individual dolphins from their battle scars -- which range from small nicks out of the dorsal fin, to major scarring following shark attacks," said Slooten
"Estimating population changes in marine mammals is challenging, often requiring many years of research to produce data accurate enough to detect these kinds of biological changes."
The study also shows that to be effective, MPAs need to be sufficiently large.
"The take home message is that size matters. Marine Protected Areas work, but they have to be large enough in order to be effective," said Slooten.