If the South Taranaki Bight is a blue whale foraging ground it will be an important area for their survival, and human activities there will need to be appropriate, Dr Leigh Torres says.
She is with a team of researchers on the Niwa vessel Ikatere, scouring the sea between Farewell Spit and Cape Egmont for pygmy blue whales until the end of February. They were offshore from Whanganui on Monday and saw no whales.
However, she and her team saw "dozens" about 100km offshore south of New Plymouth two years ago.
She was pleased rather than surprised to see them, because her research told her they should be there: "It was very gratifying to prove my theory correct and find the whales."
They would be pygmy blue whales, she said, and slightly smaller than a blue whale which can grow to 28m. They would be feeding on a species of krill, Nyctiphanes australis, at 70m-200m depths.
If the bight is a foraging ground for them it will be the fifth known such area south of the equator and an important place for them to gain energy stores to survive and breed. Activities like offshore oil drilling could affect their well-being.
All blue whales have been extensively hunted, and their numbers are depleted.
Pygmy blue whales are a southern hemisphere species that live in the Indian and southern Pacific oceans and breed in the Indian and south Atlantic oceans. The whales are known to migrate up the west coast of Australia from Perth to Indonesia.
Dr Torres would like to know where they migrate locally.
"We are not sure of their migration patterns. We hope to find this out eventually."
Her team has set five hydrophones in the water, from north of Cook Strait to west of Cape Egmont. They will record whale calls and provide information about whale movements.
While surveying the bight those aboard the Ikatere have seen other marine mammals - pilot whales, fur seals and common dolphins.
Early Europeans called the bight Mothering Bay, because mother whales calved there. Dr Torres said those whales would have been southern right whales.