University of Auckland researchers Rosalyn Putland and Associate Professor Craig Radford from the Institute of Marine Science combined sound recordings over a nine month period with automatic ship tracking data to track underwater noise contributed by shipping.
Think of being at a noisy cocktail party, where the din becomes so loud that it's difficult to hear what's going on around you, or even hold a conversation with someone near you.
Thanks to large, noisy ships, a similar effect has been observed beneath the surface of the Hauraki Gulf - and scientists say it could be making it harder for at least two resident marine species to communicate.
But its authors add that efforts to slow down ships to reduce the risk to whales had also been having benefits for noise.
University of Auckland researchers Rosalyn Putland and Associate Professor Craig Radford from the Institute of Marine Science combined sound recordings from four hydrophone "listening stations" over a nine-month period with automatic ship tracking data to track underwater noise contributed by shipping.
Suspended 1m to 2m above the seafloor, the hydrophones recorded two minutes of data every 20 minutes.
The study focused on two species which use sound to communicate, Bryde's whales and the common reef fish, bigeye.
Every time a vessel passed within 10km of a listening station, it reduced communication space for bigeye by up to 61.5 per cent and by up to 87.4 per cent for Bryde's whales.
Research has shown bigeye can communicate over distances of up to 31m - suggesting that passing ships could reduce this to less than 12m.
Suspended 1m to 2m above the seafloor, the hydrophones recorded two minutes of data every 20 minutes. Photo / University of Auckland
Bryde's whales, meanwhile, were capable of communicating from as far away as 8km from one another.
Radford said this was called the "communication space" between species.
University of Auckland researcher Rosalyn Putland listens to sounds collected by seafloor hydrophones in the Hauraki Gulf. Photo / Jared Kibele
"Communication space is the range at which two species can hear each other and this study has found the range at which bigeyes and Bryde's whales can communicate is significantly reduced when a ship comes past."
The reduction of communication space for marine species was becoming an increasing concern for scientists worldwide as more was learned about how the use of sound is used among groups of species to ensure survival including finding a mate, defending territory and warning of predators.
The biggest impact from ship noise was at Jellicoe Channel, the most regularly used shipping lane into Ports of Auckland where vessel passages were recorded 18.9 per cent of the time.
Image / Supplied
This latest study provides further evidence that compliance with the 10-knot speed restriction within the Hauraki Gulf Marine Park area could benefit marine species, Putland said, as vessels travelling at lower speeds produce lower levels of noise.
"The voluntary speed limit of 10 knots is fairly recent but we believe it is having a significant effect on helping reduce noise in the gulf to allow species to hear each other," she said.
"Even so, when a ship is directly above marine animals, it reduces communication for those animals almost completely, or by 99 per cent."
Ports of Auckland head of communications Matt Ball said it was pleasing to see the work to reduce whale deaths caused by shipping was also helping reduce ship noise.
"As the report's authors note, the voluntary speed limit of 10 knots is having a significant effect on helping reduce noise in the Gulf to allow species to hear each other," Ball said.
"The shipping industry is right behind the voluntary speed restriction and as a result there have been no whale deaths from ship strike for over three years."
While this study focused on large commercial vessels, more than 130,000 recreational boats regularly use the gulf and this number is expected to rise 40 per cent in the next 20 years.
Every time a vessel passed within 10km of a listening station, it reduced communication space for bigeye by up to 61.5 per cent. Photo / University of Auckland
Recreational boats produced sound that also overlapped fish and marine mammal vocalisations.
Further research at the Leigh Marine Laboratory will focus on how recreational boat noise in the gulf affects the communication space of fish and marine mammals.
The new findings came after US scientists Dr Leigh Torres, of Oregon State University, and Dr Holger Klinck, of Cornell University, aired their concerns over the noise created by seismic air guns, which are used by the oil and gas industry to search for new reserves.
Klinck and Torres shared underwater recordings made in the South Taranaki Bight capturing an oil survey ship letting off seismic blasts every eight seconds.
When sped up, the recordings showed how the sound was enough to drown out the call of a blue whale - a species known to feed in the area.
The researchers said whales used sound to communicate, find food and navigate, and seismic blasting meant their lives were "disturbed and dramatically altered".
A consistent, repetitive boom was what whales living in a region of oil and gas exploration heard, as seismic surveys often lasted several months.
Industrial seismic airgun arrays were among the loudest man-made sources and the noise emitted by these arrays could travel thousands of kilometres, they said.
Noise from a single seismic airgun survey could blanket an area of more than 300,000sq km, raising local background noise levels 100-fold.
