Seismic surveying likened to "a nail gun for three months in your kitchen" for marine mammals could also be affecting the world's smallest species of penguin.
New findings of the first ever study investigating effects of seismic testing on penguins could hold serious implications for a population of little blue penguins, or korora, living on the South Taranaki Bight.
The fresh concerns come after two US scientists recently released underwater recordings capturing an oil survey ship letting off loud seismic blasts in the bight every eight seconds - enough to drown out the sound of blue whales known to feed in the area.
Now, a South African study has shown how endangered African penguins avoided their preferred feeding grounds when survey vessels were operating.
Four months of seismic testing by the world's largest oilfield survey company, Schlumberger, is currently underway in the Taranaki Basin.
While the study showed the penguins behaved normally again once testing stopped, it was unclear whether there had been any permanent effect on the birds' hearing, or whether they'd missed a critical feeding window, Forest and Bird seabird expert Karen Baird said.
"Five out of six of New Zealand's native penguins are in trouble, including the little blue penguin," she said.
"Recent research of the little blues, which breed on Motuara Island in the Marlborough Sounds, shows they swim all the way to the Taranaki Bight, a return journey of 170km.
"This huge effort means the bight is likely to be an important feeding area for them, and the seismic testing which is underway there could very well be disrupting their feeding and breeding success."
Other experts approached by the Herald shared Baird's concern.
"I don't see why it wouldn't hold for our little penguin, especially if the blasting overlaps with foraging habitat like in the South African study," University of Auckland marine scientist Associate Professor Craig Radford said.
"These little guys spend a considerable amount of time at sea foraging and if they are as sensitive to sound as the South African species then there is the potential to disrupt their foraging behaviour."
Dr John Cockrem, a professor of comparative endocrinology at Massey University, said the South Taranaki Bight was within the Cook Strait Important Bird and Biodiversity Area, and hence an area of international significance for the conservation of the world's birds.
"Seismic surveys conducted within 100km of korora foraging areas could have adverse effects on breeding success and survival of the penguins," he said.
"The extent to which previous and current seismic surveys conducted in New Zealand coastal waters may have adversely affected penguins is not known."
Massey wildlife veterinarian and Wildbase Research Centre director Dr Brett Gartrell said the new findings would be a concern if they held true for korora, although there was nothing yet to show that birds' hearing had been affected by the blasting.
"To date, we have no evidence that seismic surveys are causing pathology in New Zealand birds, although this study suggests that the birds' behaviour may be affected before damage is done."
Department of Conservation marine species and threats acting manager Kris Ramm said potential effects on blue penguins was now emerging as an "issue of concern" following the new study.
"We have no knowledge about whether the penguin species breeding here in New Zealand would behave in a similar way to the African penguins, but it seems likely."
DoC had no management plans to minimise the impact of seismic testing on little blue penguins in the South Taranaki Bight or elsewhere.
Most research on seismic effects to date looked at whales, dolphins, seals and turtles.
However, Ramm said, there were mitigation measures in place to prevent harm to marine mammals through the seismic survey Code of Conduct, which required vessels to cease activity if animals were detected with a one-kilometre radius, or 1.5km if young animals were involved.
Procedures in the code, including "soft starts", where power was gradually increased over time, could allow seabirds to detect and move away from the noise source.
"The code is considered to be one of the most rigorous in the world for protecting marine mammals and requires having independent observers on board survey ships both watching and listening for animals," Ramm said.
"The research from South Africa provides useful new information about penguins which will be carefully considered in future decisions about the management of seismic surveys generally."
Petroleum Exploration and Production New Zealand (PEPANZ) chief executive Cameron Madgwick said the industry was "very conscious" of minimising any impacts on marine life.
Little blue penguins had been covered in the Marine Mammal Impact Assessment prepared for the current survey as a species potentially in the survey area for long distance foraging, and any sightings were being reported to DOC.
"As far as we know there hasn't been any specific modelling or research done for this species in New Zealand so it isn't clear how applicable the South African research is," Madgwick said.
"There would need to be more detailed local research before we could reach any conclusion."
Madgwick said the sound generated by seismic acoustic work was around 230 to 255 decibels, which he added was a similar level to some natural sounds.
"This sound also dissipates rapidly in the water - at one kilometre from the source the sound levels have generally dropped below 171 decibels, which is lower than the noise from large commercial shipping vessels."
However, the US scientists who recently undertook a study in the South Taranaki Bight argued noise from a single seismic airgun survey could blanket an area of more than 300,000sq km, raising local background noise levels 100-fold.
"Imagine someone operating a nail gun for three months in your kitchen and you have nowhere else to eat," Dr Leigh Torres, of Oregon State University, and Dr Holger Klinck, of Cornell University, wrote in a blog post outlining their work.
"The evidence has mounted. There is no longer a scientific debate: seismic airguns are harmful to marine animals and ecosystems."