Unexpected upside to lockdown – Listening in to dolphin chatter

What happens to whale, dolphin and fish communication when human noise is turned right down? Before Covid-19 and New Zealand subsequently going into lockdown, the opportunity to find out was impossible. Thankfully, a research project led by Dr Matt Pine recorded the moment when noise pollution in the Hauraki Gulf Marine Park/Ko te Pātaka kai o Tīkapa Moana dramatically dropped five-fold.

Since January 2020, Dr Matt Pine and colleagues have been acoustically monitoring the presence of cetaceans, fish and vessels in the Hauraki Gulf Marine Park as part of their DOC-funded research project. When lockdown occurred, five stations located in the waters of the Rangitoto Channel, Torbay, The Noises, Tiritiri Matangi and the outer Gulf, documented the drop in the presence of daily vessel noise from an average of 70% per day to a jaw-dropping 8% a few days after Alert Level 4 came into place. For those acoustic nerds out there, the general daily average noise levels in the Gulf decreased by 8dB, which is approximately a 5.3-fold drop in the acoustic energy that marine animals were exposed to before the lockdown.

With lockdown rules halting non-essential travel, including leisure boating, the Hauraki Gulf was almost void of people and vessels.  In stark contrast,  the Gulf was the most alive it has ever been in recorded history with hydrophones documenting the simultaneous sounds of dolphins clicking and whistling, fish grunting, invertebrates moving around the listening stations, and waves crashing on the shoreline 3-4km away.

Marine mammals, fish and invertebrates depend on sound for critical life processes. They use sound to locate prey, navigate, find mates, socialise, keep groups together, avoid dangers like predators and more. Their ability to hear these biologically important sounds over vessel noise is a key concern of noise pollution on these species.

The sudden drop in noise had a direct effect on species. The range by which dolphins could communicate more than doubled immediately, and interestingly, dolphins were detected for far longer periods than before lockdown in The Noises (a total of 1341 minutes over 31 days before lockdown, compared to 2031 minutes over the same amount of time during Alert Level 4).  Fish are more complicated in their hearing biology, but the effects were the same – massive increases in their ability to communicate over longer ranges.

The initial project focused on the potential impact of tourism operations on the acoustic wellbeing of whales and dolphins in the Hauraki Gulf Marine Park. The research, led by Dr Pine with the University of Auckland, University of Victoria in Canada and Styles Group Underwater Acoustics in Auckland, was awarded $30,000 in 2019 by DOC, funded by tourist operator concessionnaires including Auckland Whale and Dolphin Safari and Dolphin Planet.

The first long-term listening station was installed in early January 2020, followed by another four, all of which contain a Kiwi-built acoustic recorder. This meant that recordings began at the peak of summer when vessel numbers were at their highest and have been recording the ocean continuously since then.

Initial data analysis involved determining if the vessels were commercial or recreational, measuring noise levels over each day, and automatically detecting dolphin echolocation clicks and whistles, as well as whale calls. The data was then used to calculate the range over which individual dolphins can communicate with one another while moving around the Gulf. Data was also used to quantify the influence of small and recreational vessels on the soundscape, including cumulative sound exposures to marine mammals and fish.

But of course, the research never expected to be able to study the impact of vessel noise at levels of, almost, zero. This precious data give the researchers the unprecedented opportunity to explore a multitude of questions. By removing recreational and small vessels from the Gulf, Dr Pine and his team can study the impact of small vessels on marine mammals, the potential acoustic impact of commercial shipping on the Hauraki Gulf – something of particular interest if the Ports were to move – as well as the opportunity to learn more about the Gulf’s resilience in response to positive change.

For this project however, Dr Pine’s research aims to discover the true influence of small boats on dolphins and fish of the Hauraki Gulf by establishing the empirical, real, correlations between the number of small boats operating in an area with ambient sound levels. All of which means they will be able to predict how a future increase in boat traffic will change a soundscape and thus dolphin and fish communication.

The listening stations will continue to monitor the Hauraki Gulf until early 2021, so that Dr Pine’s team can compare two summers. We’ll be sure to keep you in the loop about confirmed findings after the research is completed.

Love it, Restore it, Protect it.