“Ambitious, innovative” survey reveals more Hector’s dolphins
The most intensive marine aerial survey ever conducted in New Zealand has revealed there are potentially twice as many endangered Hector’s dolphins as previously thought – but they’ve been found far outside our banned trawling and set-net areas.
Led by Cawthron Institute, the three-year survey to update Hector’s dolphin numbers and distribution has revealed there could be between 12,000 and 18,500 nationwide. The last published estimate was just over 7000. The survey, commissioned by Ministry for Primary Industries, received a landmark endorsement from the International Whaling Commission (IWC).
Project Leader and Cawthron Institute marine mammal ecologist Dr Deanna Clement, who studied Hector’s dolphins for her PhD, says that “while the numbers are reassuring, just because there are more of them it doesn’t mean they’re okay – they are still at risk as we’ve now found significant numbers in unprotected waters and there’s still a substantial overlap between fisheries’ areas and the dolphin’s distribution.”
VIDEO: A ground-breaking marine aerial survey of New Zealand's South Island has revealed endangered Hector's dolphins can be found much further out to sea and there are potentially twice as many of them as previously thought.
Endemic to New Zealand, Hector’s dolphins are one of the world’s rarest dolphins and, at only 1.4m long and 50kg, they’re also the smallest. Set nets and trawl fishing are the biggest threats to the species and New Zealand has banned these fishing practices up to four nautical miles offshore around most of the South Island to protect them. The dolphins were previously thought to be a mainly inshore species, however, Dr Clement’s team found up to half the population in unprotected waters beyond four nautical miles offshore.
“While there had been unconfirmed sightings as far out as 15 to 16 nautical miles offshore, up till now it had been difficult to accurately survey that far out to sea in New Zealand,” Dr Clement says. “To overcome this, we developed new survey and mathematical methods which enabled us to venture further out and collect more accurate data to really get a handle on the numbers.”
The survey was the most intensive marine aerial survey ever conducted in New Zealand, involving 675 flying and helicopter hours and covering a survey area of 75,196km2 which was surveyed twice (in summer and winter) - totalling an area the size of the South Island.
Co-researcher and director of Proteus Wildlife Research Consultants, Dr Darryl MacKenzie, designed the survey protocol and modelled all the resulting data – including creating some innovative analytical techniques. He says the survey provided a number of challenges.
“There were a quite a few novel aspects that required us to extend and develop approaches that have been used in previous aerial surveys for Hector's dolphins in New Zealand, and for other marine species internationally.” They included how to accurately determine what fraction of the dolphin population were underwater when the aircraft flew overhead and couldn’t be seen by the observers.
“Another aspect is that in New Zealand, the types of planes available for the survey do not enable both observers on the same side of the aircraft to search the exact same areas,” he says. “Existing statistical analysis methods didn't allow for this so new approaches had to be developed. These developments are going to be useful to researchers conducting similar survey work elsewhere in the world.”
MacKenzie says everyone had been expecting estimates along the South Island's East Coast to be about 2000 to 3000, instead they found between 8000 and 9000 Hector’s dolphins.
“So when our first estimates for the summer survey came back to be more like 9000, we were very surprised and went back to double- and triple-check our work. Since then our work has been scrutinised at several technical working groups convened by MPI and by a number of international experts.”
He says the result is that these are by far the most intensely reviewed Hector's dolphin abundance estimates ever produced.
The survey was carried out on behalf of the Ministry for Primary Industries to provide up-to-date abundance and distribution estimates for its upcoming review of the Hector’s dolphin Threat Management Plan with Department of Conservation (DOC).
MPI presented the survey reports at the International Whaling Commission’s (IWC) annual meeting in June for endorsement. This is the first time the IWC’s Scientific Committee has reviewed and endorsed an external existing marine mammal abundance estimate, which is considered suitable for management purposes. The IWC report says the study addressed several difficult questions that did not have easy answers, and the independent expert group commended the “ambitious and often innovative work undertaken by the authors to attempt to deal with all of these issues”. It also said it was a step forward in the general evolution of survey methodology development.
About Hector's dolphins
Hector’s dolphins are one of the world’s rarest dolphins, and at only 1.4m long and 50kg, they’re also the smallest. Found only in New Zealand waters, they have been listed as endangered since 2000. No comprehensive population counts have been done for over a decade. The last published estimate was just over 7000, less than a quarter of the 30,000 thought to have existed in 1970. The population is thought to be in decline. Find out more about Hector's dolphins on the Department of Conservation's website.
Find out more:
Download the report 'Abundance and Distribution of WCSI Hector’s dolphin'
Read the International Whaling Commission report endorsing the survey findings (see page 78 of the main report, or Appendix 2 of Annex M, page 15 – 8.3 Hector's dolphin)
Watch the ONE News report 'Hector's dolphin population 'double' previous estimates'
Read the New Zealand Government's response to the new findings
Read 'When dolphins are your day job' - an interview with Deanna Clement in the Nelson Mail
For more information contact:
Dr Deanna Clement
Marine Mammal Ecologist, Cawthron Institute
Phone: +64 3 539 3295
Mobile: +64 21 151 6056
Dr Darryl MacKenzie
Senior Biometrician/Director Proteus Wildlife Research Consultants
P: +64 3 4861168
M: +64 21773108