By Conan Young of RNZ
The Cawthron Institute says a lack of rules controlling underwater noise is putting at risk some of our most endangered mammals.
The institute has been monitoring increasing amounts of noise created by pile driving, ports and recreational boats, and found it can cause temporary or even permanent deafness in whales and dolphins.
A biologist with the Cawthron Institute, Dr Simon Childerhouse, said noise pollution got in the way of them communicating with each other and could cause stress, leading to declining birth rates.
"Loud noises have the potential to physiologically injure them and their hearing either temporarily or permanently, which obviously has big implications for survival. Some of the really loud noises like seismic surveys or military sonar can also actually directly kill marine mammals."
Childerhouse said there were lots of things ports and boaties could do to reduce their impact but, at the moment, this was mandated through the resource management act and done in a piecemeal way.
The Department of Conservation, which was responsible for protecting mammals such as endangered Hector's and Māui dolphins, should bring in a set of regulations for everybody to abide by, he said.
"The European Union has some excellent underwater standards. The USA also has some standards and even Australia has some some guidelines in some states. So New Zealand's a bit behind."
The Lyttelton Port Company was the first in the country to take steps to protect its local Hector's dolphins and employed observers to spot them during pile driving for its new cruise ship berth.
Its head of Environment, Kim Kelleher, said work stopped - sometimes for up to several hours - whenever they came close.
"It's something that needs to be done to make sure that the dolphins are protected. So, like anything else in terms of the methodology of the project, these are just things that need to be factored into the project.
"We're really fortunate, it's an amazing environment and, you know, to have Hector's here, a conservation species, a taonga, it's amazing."
Kelleher was fully supportive of the development of regulations that all ports could use to keep these species safe.
Underwater acoustic expert, Dr Matt Pine, said it's normally to gauge if things were getting noisier underwater because the sound made by boats was almost always there.
That was until last year's lockdown when boaties were forced to stay moored for almost two months.
Dr Pine couldn't believe his ears when he pulled up the five hydrophones that had been recording right through the period.
"It was pretty amazing, sort of going back to what it would have been like you know before [Captain James] Cook and hearing seal calls and whales and dolphins and fish, and waves rolling on a distant beach."
With the base pre-industrial level established, Dr Pine was now able to predict how much louder it was likely to get in the gulf over the coming years, especially from recreational boats which created most of the noise.
With ownership forecast to increase 38 percent in the next two decades, it may eventually become too noisy for marine mammals or even the fish the boaties were looking to catch, he said.
"Sound impacts fish right down to the larvae where they orient towards sounds like reef sounds and, if they can't hear the reef sounds, they won't swim in. So they'll end up in areas that are not in the Hauraki Gulf."
A DOC spokesperson said addressing the problem would require an amendment to the Marine Mammals Protection Act.
This would involve a "substantial piece of work" and would need to be weighed against "other priorities."
For now it would continue to use the RMA to help protect them.