A research team is looking for blue whales off the lower North Island west coast after "dozens" were sighted there two years ago.
The Conservation Department (DoC) is working with Dr Leigh Torres of Oregon State University on the three-year project.
She and her team saw dozens of blue whales feeding about 100km off the coast south of New Plymouth two years ago.
The team, supported by two DoC marine specialists, is back looking until the end of February. The large area they are covering is known as the South Taranaki Bight and extends from Farewell Spit to Cape Egmont.
They are using the National Institute of Water and Atmospheric Research (Niwa) vessel Ikatere, heading out from Golden Bay. Their work is financially supported by the private environmental Aotearoa Foundation..
There are only four confirmed blue whale foraging grounds in the southern hemisphere, outside of Antarctic waters.
In the past any whales seen in the South Taranaki Bight were assumed to be passing through on a migration.
Dr Torres wants to know when and where they feed there, how many are there, how long they stay and whether they return regularly.
The researchers are to place hydrophones in the sea, to record blue whale calls for the next two years and help them learn about whale movements.
They will also take photographs, to identify individuals, and tissue samples to analyse genes and find out more about the population.