Oil exploration a threat to whales?

BIG EFFORT: Rescuers struggling to return an orca to deeper water at Ruakaka.

Marine mammal expert Dr Liz Slooten, from Otago University, has raised concerns that whales and dolphins may be endangered by sonar and seismic exploration for deep sea oil in Statoil's permit zone off Northland.

"Gray's and Cuvier's beaked whales, and sperm whales, live off Northland's west coast," Dr Slooten said.

"Beaked and sperm whales are sensitive to seismic sonar explosions for oil exploration that can damage hearing, which whales rely on to navigate, and they can be killed if they're very close to the sonic explosions."

Stationing observers on oil survey vessels was "virtually useless", and does very little to protect whales, she added.

Overseas research had shown that observers on seismic testing ships only saw around 10 per cent of whales and dolphins in the area, because sperm whales, for example, spent 45 minutes diving and feeding for every 10 minutes they spent on the surface taking in air.

"Most of the whales that are sensitive to noise will be on the run, or already be in deep trouble, before the observers can see them," she said.

"Seismic survey noise can be heard for at least 80 kilometres, but the observers can see whales and dolphins for only one or two kilometres, and then only when they surface.

Small species, like Maui's dolphins, are also very difficult to see if they are more than a few hundred metres from the vessel."

About half of the world's whales, dolphin and porpoise species lived in New Zealand waters, often travelling huge distances around the country at different times of the year.

Dr Slooten said there were three major concerns for whales that were alarmed by sonar:

* Fleeing to escape the sounds could push them into areas of other risks (eg netting);

* Because sound travelled further in deep water, they may head for shallower and shallower water where the sonar noise fell away more quickly, and end up beaching themselves;

* Beaked whales, which normally fed at depth off Northland, could panic and try to surface too quickly, resulting in the bends and possibly death.

"There have never been extensive surveys of whales and dolphins off Northland's west coast. That means there is no baseline data to see if things change with deep sea oil surveys or drilling," she said.

"However we do know there are unusual and rare species of whales and dolphin present from the animals that have beached along Northland's west coast over the past few decades, and from surveys carried out close to shore for Maui's dolphins."

A rare pygmy sperm whale had beached earlier this year on the Raglan coast while seismic testing was being carried out on for oil and gas. The cause of death was unknown, because it had been shot and buried before an autopsy could be conducted.