An oilfield services company doing seismic surveys of the sea floor near Cook Strait says they are not linked to recent whale strandings.
The company, Schlumberger, said it adhered to strict environmental protection measures for geophysical surveys.
Recent strandings of whales rarely seen in shallow waters - a grey-beaked whale in Caroline Bay in Timaru on 26 December and a sperm whale at Rabbit Island, Nelson on 30 December - have got scientists and environmentalists wondering why.
Otago University zoologist Liz Slooten said the Rabbit Island stranding happened at the time one of the surveys was being conducted off Taranaki, which was 60 nautical miles (111km) north of Nelson.
"The whale could have been very close to the air guns and may have suffered physical damage causing temporary or permanent hearing loss. This could have led to the stranding, but only a full autopsy can answer this question," Professor Slooten said.
Schlumberger was operating east of Cook Strait. Spokeswoman Ariane Labadens said in the past three years it operated in New Zealand it had funded Department of Conservation (DOC) facilitated whale necropsies and no deaths were found to be the result of seismic operations.
She said whale strandings were a difficult sight, but the recent ones were outside the active operations area.
Ms Labadens said the company was committed to environmental protection.
Measures it took for the current New Zealand geophysical survey met and exceeded DOC requirements for minimising acoustic disturbance to marine mammals, she said.
Ms Labadens said two qualified marine mammal observers and two passive acoustic monitoring operators were on board at all times.
"The observers look for mammals in the vessel's vicinity, while the acoustic monitoring system operates 24 hours a day to detect vocalisations. If a whale comes within one kilometre of the seismic source, the operation is shut down immediately."
Ms Labadens said if calves were seen or detected in the pod, the safe operating zone was extended. She said Schlumberger had iwi on board as part of their training to become qualified marine mammal observers.
Professor Slooten suggested the oil research companies should put up a bond to help cover the cost of necropsies on stranded whales. She understood there was no necropsy on the whale that stranded in Nelson partly because of a lack of funds.
"If it [the bond] was $50,000, honestly that would be petty cash for these companies. They're spending about $1 million a day on these surveys," she said.
A second company, PGS, which had been doing seismic surveying in Taranaki, said it also operated strictly in accordance with DOC requirements.
Spokesman Bard Stenberg said PGS was committed to funding a necropsy for any whale stranded in proximity to active operations, in consultation with DOC.
Sperm whale too big to move
DOC Motueka operations manager Chris Golding said staff tried to bury the whale with two large diggers, but had been unable to do so because of the whale's immense size and weight.
It was thought to weigh 50 tonnes or more.
The whale was tethered to prevent it floating off from where it was beached in a tidal area.
DOC staff were considering options for disposing of the whale, including letting it decompose naturally in the tide.
Mr Golding said this was successfully done with three sperm whales that stranded in Golden Bay in late 2014.
Local iwi blessed the whale and removed its jawbone and teeth as agreed under DOC protocols.