Sliding towards extinction
One of the world’s smallest dolphin species, Hector’s dolphin is also one of the most highly endangered, with fewer than 7,500 individuals remaining. Found only in waters around New Zealand, the species is gradually sliding towards extinction, due mainly to entanglement in fishing nets.
A subspecies from New Zealand’s North Island, known as Maui’s dolphin, is particularly endangered, with recent figures suggesting it is down to just 55 mature individuals.
Increased survival rates
The Banks Peninsula Marine Mammal Sanctuary was established in 1988 in an attempt to protect the dolphins from fatalities associated with the fishing industry. Researchers who have studied the dolphins in the area for 21 years found that their survival rate has increased by 5.4% since the sanctuary was declared.
“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, one of the researchers.
The team of scientists used regular photo identification of Hector’s dolphins in the Marine Mammal Sanctuary to monitor their population, starting two years before the area was officially protected. The results of the research are published in the Journal of Applied Ecology.
“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,” said Dr Slooten. “It seems to take a long time for a dolphin population to respond to protection, and therefore a long-term study to detect [any] improvement.”
Good news and bad news
Unfortunately, although the increased survival rate of the dolphins is a positive step, the researchers were surprised that it had not increased further.
“Once the Banks Peninsula area was protected, we had expected the problem to be solved and the population to be healthy and recovering,” said Dr Slooten.
Instead, the team found that the dolphins were not spending the whole year in the protected area, with some moving up to 16 nautical miles outside of the area in winter. Continuing mortality in fishing nets means that the species as a whole is still on course to becoming extinct.
According to Dr Slooten, “The good news is that the situation has improved. The population was doing a nose-dive, declining at 6% per year, and now it’s only declining slowly [at] about 1% per year.”
“The bad news is that the protected area is still too small. It would need to be extended further offshore to allow the population to stop declining and better still to grow and recover towards its original population size.”
Step in the right direction
Although the Marine Protected Area has not yet ensured the long-term survival of Hector’s dolphin, it is thought to be a major step in the right direction. The New Zealand government is now considering whether to extend Marine Protected Areas where Hector’s dolphins are found.
Speaking about the findings of the research, Dr Barbara Maas, Head of Endangered Species Conservation at NABU-International – Foundation for Nature, said, “This is excellent news because it proves that the removal of fishing nets from their habitat benefits threatened marine mammals. However, it also shows that unless a Protected Area is large enough, this positive influence cannot compensate for mortality caused by fishing. The net effect is continued decline.”
Conservationists are calling for a ban on all gillnet and trawl fishing throughout the entire range of Hector’s dolphin.
Liz Shaw, ARKive Species Text Author