The discovery of pockets of oil trapped in the wreckage of the Rena has given a Maori hapu more hope that the Bay of Plenty Regional Council will find in favour of the total removal of the wreck off Astrolabe Reef.

Matire Duncan of Papamoa hapu Nga Potiki's resource management unit said she was surprised by estimates of the quantities of oil still trapped in the wreckage. Roger King of the salvage and wreck removal consultancy TMC said the quantity of oil was believed to be less than a tonne.

"We won't know the amount we are dealing with until the recovery operation is completed," Mr King said.

In December, eyewitnesses told the Bay of Plenty Times of 'big blotches' of oil that could be seen at the reef but Rena authorities dismissed the sightings as patches of krill.

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Ms Duncan said the discovery of the oil along with environmentally hazardous debris left in some containers would put a different light on the application by Rena's owner and insurer to leave what remained of the vessel on the reef. Nga Potiki was also concerned about the risk to bird and sealife from the oil that had been leaking from the wreckage during clean-up operations.

Her comments followed the announcement by the owner's spokesman Hugo Shanahan that seven pockets of oil had been located at depths of 35m to 48m inside the engine room and what remained of the accommodation block. Planning was under way to recover the oil, although he was unable to give a date. "It could be a couple of days or a couple of weeks."

Mr Shanahan could not estimate how much oil was left in the wreckage, saying diving was being done at such depths that it was hard to be accurate.

With the right planning he believed divers could release the pockets of oil and trap the oil as it came to the surface.

The oil escaped from the wreckage as little droplets that rose to the surface and dispersed quickly. The small quantities meant it evaporated.

Mr King said the operation to find the oil was in response to sheens of oil surfacing during clean-up operations.

Small quantities of oil had escaped periodically during the clean-up but were difficult to recover.

The regional council and Maritime New Zealand had been briefed on the situation. Both authorities supported the action being taken.

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A total of 3344 tonnes of debris have so far been recovered from Rena's debris field.