Twenty-one years of research into the population of Hector's dolphins by mostly University of Otago researchers within the marine protected area off Banks Peninsula has shown the protected areas significantly improved survival of Hector's dolphins.
The study, published yesterday in the British Ecological Society's Journal of Applied Ecology, was conducted between 1986, when the area was established to reduce gill net deaths of the dolphins, and 2006.
Associate Prof Liz Slooten, one of the researchers, said the team regularly photo-surveyed the dolphin population, identifying 462 from their "battle scars" and studied their survival.
Mathematical models were then used to assess the impact of the MPA on marine mammals.
The results showed that since the MPA was put in place, the dolphin's survival increased by 5.4%, Prof Slooten said.
"The study provides the first empirical evidence that marine protected areas are effective in protecting threatened marine mammals."
While survival had improved significantly, it was not enough to prevent the population from continuing to decline, she said.
"The take-home message is that size matters. Marine Protected Areas work, but they have to be large enough in order to be effective."
Associate Prof Steve Dawson, another of the study's authors, said the study was one of the world's longest-run dolphin research projects, which was how it was able to make its finding.
He hoped the study would add weight to proposals for further protected areas.
It was much cheaper and effective to prevent the population from declining than it was to rescue a critically endangered species, he said. "It's our best shot."
Nabu (Nature and Biodiversity Conservation Union) International-Foundation for Nature endangered species conservation head Dr Barbara Mass said the results of the study were excellent news but the study population and Hector's dolphins as a whole were still on the decline.
Unless the size of the 413,000ha Banks Peninsula marine mammal sanctuary was enlarged, "it will be a case of the operation was successful but the patient is dead", she said
The study was a reminder the dolphins and the almost extinct North Island subspecies, Maui dolphins, remained poorly protected, she said.
"Nabu International reiterates its call for the protection of Hector's and Maui dolphins against all gill net and trawl nets in coastal waters up to 100m deep."
