Three Greenpeace activists, including executive director Russel Norman, swam in front of the Amazon Warrior off the Wairarapa coast.

Greenpeace has been accused of overstating the dangers of seismic surveying off the New Zealand coast.

Seismic surveying involves the shooting of compressed air to generate an underground map but it is a process protested against by Greenpeace, which fears the sounds are a danger to marine mammals.

Four Greenpeace activists, including former Green Party co-leader Russel Norman, are under Government investigation after they hurled themselves into the path of an oil exploration ship that was doing such surveying off the Wairarapa coast in April.

GREENPEACE Amazon Warrior, the world's largest seismic survey ship, off the Wairarapa Coast (file photo).

But Victoria University geophysics and tectonics professor Rupert Sutherland, who has studied the science and worked on seismic surveys, said the emotiveness of the campaign was misleading and implied that seismic reflection was more harmful than the reality.

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He knew of no evidence that conclusively showed there was a single incident of a whale or dolphin being directly injured by seismic reflection vessels.

GREENPEACE Russel Norman from Greenpeace swims in front of an oil exploration ship.

Climate change researchers used seismic surveying and drilling to collect sediment cores to look at climate records, he said.

"The current strategy of Greenpeace makes it expensive or impossible to conduct legitimate research in the ocean, including climate change research."

Greenpeace climate campaigner Kate Simcock rejected the suggestion Greenpeace was misleading anyone, saying its campaigns were based on well documented scientific evidence.

Greenpeace's campaign did not make claims of direct impact to marine mammals, and the effects were chronic rather than immediate, she said.

"Seismic surveys have been shown to disrupt essential activities for whales, including foraging and reproduction.

"There could also be an increased risk of calves being separated from mothers… Exposure to repeated loud blasts from a seismic survey can mask the sounds they rely on and lead to stress, disorientation, changes in foraging and nursing behaviours, and, in extreme cases, direct physical damage."

Sutherland said while marine mammal behaviour may have been altered by seismic surveying, that was far less harm than that caused by the fishing and shipping industries.

"The thing that really causes environmental impact for marine mammals are shopping and fish and chips ... but everyone's a bit suspicious of people in suits that make lots of money in the petroleum industry, so they're kind of easy targets emotionally for Greenpeace to exploit to fund-raise."

GNS marine geophysicist Stuart Henrys, who was on the committee that wrote the 2012 Department of Conservation code regulating noise from seismic reflection vessels, said Greenpeace should have an open mind about noise in the ocean.

"Seismic reflection is a tool that's used by the industry. It's well regulated, and there's research to underpin that regulation.

"Ship noise is continuous and at a much higher volume than seismic reflection vessels, and the accumulated sound of a busy shipping lane is far greater than seismic ship noise," he said.