The research analysed data which showed dolphins are now less likely to be seen in the inner harbour, as cruise ship numbers increased. (file photo) Photo: 123rf
Cruise ships visiting Akaroa Harbour may be responsible for a change in the behaviour of Hector's dolphins in the area, new research suggests.
Hector's dolphins are one of the world's smallest dolphins, measuring about 1.5m long.
Classified as nationally vulnerable, there are about 15,700 in New Zealand's waters, primarily around the South Island.
University of Otago department of marine science researcher Will Carome analysed 20 years of dolphin survey data to determine which parts of Akaroa Harbour dolphins were being seen in and compared it to trends in cruise ship and dolphin tourism.
Almost 370 surveys, recording 2335 dolphin encounters from 8732km of boating, were analysed.
The research showed a clear shift, with dolphins now less likely to be seen in the inner harbour, as cruise ship numbers increased.
While the research did not prove exactly what caused the distribution change, it suggested disturbance from cruise ships was the most likely explanation.
In summer 2009/10, Akaroa hosted seven ships and 6222 passengers. By summer 2011/12, there were 77 ships visiting the harbour, bringing in 127,341 passengers. Large numbers continued to visit until Covid-19 restrictions began in 2020.
Akaroa Harbour in Te Pātaka o Rākaihautū (Banks Peninsula) is valuable habitat for the dolphin, which are a drawcard in the marine tourism industry.
Carome said the correlation between more cruise ships visiting and changes in Hector's dolphins' distribution did not necessarily mean cruise ships were the cause of the changes.
Other potential drivers, such as changes in sea temperature or prey distribution, could have played a role in the shift.
"However, there are several impacts associated with cruise ships that are likely to influence dolphin habitat preference, including increased noise, increased vessel traffic, and damage to the seafloor that may impact species Hector's dolphins eat," Carome said.
The Covid-19 pandemic provided a remarkable opportunity to give marine life short-term relief from some human impacts, he said.
"With the future of cruise ship tourism changing, our findings suggest the future development of this industry should follow a precautionary approach."
Department of Conservation (DOC) mahaanui operations manager Andy Thompson said the department was working alongside Ōnuku Rūnanga, Environment Canterbury, tour operators, researchers, and the community to protect the dolphins and reduce potential impacts of cruise ships, dolphin tour vessels, and general vessel traffic.
"The Hector's dolphins are an important part of Akaroa and the people who live here feel a strong connection to them," Thompson said.
"We want to work with local people to find solutions that benefit everyone and are also focused on the wellbeing of the dolphins."
In 2010, research highlighted Akaroa's Hector's dolphin population had been exposed to some of the highest tourism pressure in New Zealand and the activity was shown to significantly change their behaviour.
In 2016, DOC placed a 10-year moratorium on the issuing of any new marine mammal tourism permits in Akaroa Harbour and commissioned the University of Otago to conduct additional research to fill knowledge gaps and inform further permit/vessel traffic management decisions.
This new research was paid for by a research levy collected from the operators.