Lockdown study of Hauraki Gulf shows dolphins communicate better with fewer boats

Thursday, 22 July 2021

The Hauraki Gulf - which lies between Auckland, the Coromandel peninsula and Great Barrier Island - is threatened by overfishing, climate change and a population boom. (Video first published in March 2018)

A study of the Hauraki Gulf during last year’s Covid-19 lockdown has revealed the effect noise pollution may have on the way marine organisms communicate.

The lockdown and resulting absence of smaller, non-essential boats in the gulf presented University of Auckland marine scientists with a unique opportunity to measure how human activity may affect wildlife.

“We decided to take a look at the response of our marine organisms in this new, relatively calm world,” associate professor Craig Radford said.

Bottlenose dolphins were able to communicate with each other from more than double the usual distance when there was less noise disturbance from boaties during last year’s Covid-19 lockdown. (File photo)

He added that research into the noise made by smaller boats had previously been “somewhat neglected” due to the larger scale noise made by ships.

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Bigeye fish could communicate with each other from up to 70m away during the lockdown, compared with just 4m prior. (File photo)

“Key data from this study provides strong evidence that small vessels, where there are enough of them, directly influence sound levels and are definitely having an impact.”

Noise pollution is known to have deadly effects on marine life, such as those which use sound for life-critical behaviours like mate selection and predator warnings.

The study, which was published in the Global Change Biology scientific journal in collaboration with Dr Matthew Pine from the University of Victoria in Canada, saw data gathered from acoustic recording stations at five sites in the Hauraki Gulf.

Between February and May 2020, six samples per hour – or 144 samples a day – were gathered and split into lockdown and pre-lockdown categories.

The study focused on how these noise levels affected the communication range of bottlenose dolphins and bigeye fish, both which are commonly found in the Hauraki Gulf.

Analysis of the samples found that without small boats, the area was much quieter, with noise levels dropping to eight per cent of normal levels.

The quieter noise levels meant the communication range – the maximum distance from which an animal can hear another animal of the same species’ vocalisation – for dolphins and bigeyes more than doubled.

For example, in the Rangitoto Channel, dolphins were able to hear each other from a distance of around 565 metres away during lockdown, compared to 400m prior.

Further away from the city, at the Ahaaha Rocks near Waiheke Island’s northern coast, the communication range increased from 2.9km to nearly 4km, and from 4m to 70m for bigeyes.

“There is a growing body of evidence that shows vessel noise is highly invasive and audible to nearly all marine mammals and fishes,” Radford said.

“The sheer number of recreational vessels in normal times is not offset by the fact they are often only present for short periods of time.”

The study did not measure whether marine life populations increased during the lockdown period, as it did not align with their reproductive cycles.

It was of Radford’s personal view that New Zealanders didn’t appreciate how much underwater noise is being produced through marine construction, commercial shipping and recreation.

He added that New Zealand was “a little bit behind in the world” compared to the likes of Europe, which had initiatives in place to limit the problem, such as working with commercial builders to make quieter ships.

“I think we can start looking at their ideas and map them for what suits us as a country.”