Nine acoustic moorings are being placed in the Manukau Harbour to learn more about the elusive, and critically endangered Maui dolphin.

Marine scientists are planning to eavesdrop on critically endangered Maui dolphins in an attempt to improve the mammals' chance of survival.

NIWA marine ecologists Dr Kim Goetz and Dr Krista Hupman are setting up a year-long research project to listen in on the dolphins' clicks and whistles.

Goetz and Hupman are deploying a line of up to nine offshore moorings – stretching 12m out from the shoreline – just south of the Manukau Harbour.

SUPPLIED Scientists hope that by listening in on the dolphins they'll be able to better understand migration and behaviour.

It is part of a collaborative project between the Department of Conservation, the Ministry for Primary Industries and the University of Auckland.

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DAVE ALLEN Dr Kim Goetz, pictured in 2016, with one of six acoustic devices deployed in and around Cook Strait.

There are between 57-65 Maui dolphins left in the world and scientists hope that listening in on the dolphins will give them insight into their migration and behaviours.

Each mooring will carry two acoustic devices to record detections of the dolphins' high frequency 'clicks', which they use to navigate and hunt prey, and a sound-trap to record clicks and whistles.

Maui dolphins are only found on the west coast of the North Island, with the greatest concentration between Manukau Harbour and Port Waikato.

While they are known to congregate close to shore in water less than 20m deep, scientists are uncertain how far offshore they travel and what risks they face in doing so.

Goetz said the first step was to establish how far offshore the dolphins could be detected.

Acoustic monitoring provides a reliable way to detect the presence of marine mammals over a long time period, she said.

"They are an endangered animal, so anything we can contribute to increasing our knowledge will be very useful."

Data will be retrieved from the moorings every three months, surveying over the course of the year to pick up on seasonal variations.

Maui dolphins, a sub-species of the Hector's dolphin, are the world's smallest species of dolphin. They only live for up 20 years, and are slow to breed.

Each year, a photographic survey of Maui dolphins is carried out to match distinguishing marks and scars with known animals.



Mark-recapture biopsy surveys are conducted across two years, every five years, to estimate the number of Maui dolphins in the area - most recently, in 2016.

While they provide a "valuable snapshot" of a given time, Goetz said the acoustic survey will add to the data by providing information gathered over the year.



DOC marine species expert Lauren Boren said it could be difficult to track the dolphins due to the small population size and the nature of the west coast.



"We've been trying to increase our 'eyes' on the water by encouraging public sightings of the dolphins, but these acoustic moorings will increase our 'ears underwater' and be there listening when we can't be watching," she said.



The project follows a similar monitoring project Goetz is undertaking in Cook Strait. Preliminary results from this project revealed recordings of vocalisations from Antarctic blue whales, minke whales and several different beaked whale species which are rarely seen.