A sperm whale washed ashore near Nelson could have died after becoming disoriented by seismic research north of Tasman Bay, a zoologist says.
Otago University zoologist and researcher Liz Slooten said other possibilities were a fishing vessel hit it, or it got tangled while eating off a longline.
Without an autopsy it was hard to say, she said.
The whale, which beached on Rabbit Island near Nelson yesterday, was one of several seen in the bay in recent days, and which was initially thought to have been a humpback or right whale.
Dr Slooten said it looked too well to have died of natural causes.
She said the fully grown male, which was still young, could have died after becoming disoriented by seismic research being done north of Tasman Bay.
An online ship-tracking system showed two seismic research vessels had been operating seismic detectors each side of Cook Strait - one in the Taranaki Basin, north of d'Urville Island across to Farewell Spit and up to New Plymouth, the other east of Wellington.
The technology pinpointed areas for oil drilling, or studied the geology of the sea floor by towing equipment which shot loud blasts of compressed air through the water and deep into the seabed. The waves reflected back information about buried oil and gas deposits.
Dr Slooten said Cook Strait was an occasional transit zone for sperm whales, which normally lived in ocean depths of up to 1000 metres - and never in shallow depths such as those in Tasman Bay.
"With these seismic vessels happening on both sides of Cook Strait, it is conceivable the noise from one of these two vessels confused it and it's fled, then heard more of the same noise ahead and it's tried to escape, but we'll never be able to prove, or disprove that," Dr Slooten said.
She said seismic noise travelled several hundred kilometres. There were several instances overseas sperm and beaked whales stranded near vessels operating sonar equipment.
"When you make a noise offshore, beaked whales in particular will flee inshore."
Dr Slooten said deep scars on the whale's side could be from a ship's propellor, but again it was hard to say.
The line of small sharks and fish-heads washed ashore near the whale indicated it might have become tangled with a fishing vessel while eating fish off a longline.
She said sperm whales often got cheeky and went up to boats to take fish off lines.
Residents first spotted the whale offshore on Thursday.
At that time, Dr Slooten said the fact the whale was in shallow waters - and the way it was behaving - indicated it was unwell and confused.
She said sightings of other whales nearby at the time the whale stranded, and following after a yacht on Tasman Bay, were unusual but not impossible.
"Sperm whale females and calves come about as far south as Cook Strait ... when the males reach sexual maturity the leave the group.
"One of the size in Nelson will generally be solitary and roving from one group to another, and mating with the females."