New Zealand scientists will depart Wellington next month on the tail of the sperm whale in Antarctica.
A programme lead by National Institute of Water and Atmospheric research (NIWA) will take 20 scientists on the research vessel Tangaroa to the Ross Sea, Antarctica.
NIWA principle scientist Matthew Pinkerton will be departing with the 40-day expedition, which will be the third in a series of four voyages.
On previous trips they had put down moorings with attached hydrophones, to listen to sounds from the sperm whales on the edge of the Ross Sea – the best way to count how many were in the area.
"Those first moorings went down in 2018, we got them back in 2019 and put some new moorings down," he said.
"So when we go down there in 2021 we'll be picking up those moorings from two years ago so we're really excited about seeing what sounds the sperm whales might have picked up.
"It will certainly show us if there are some sperm whales there and what times of the year they're around."
Sperm whales were unlike seals in that they could not make holes in the ice, so had to find holes in the ice where they could come up for air.
Pinkerton said at some points in the year there may be too much ice for the sperm whales to survive, so their research was crucial to determining where the populations were.
"They've got moorings at different latitudes, so certain distances south. We want to see if the sea ice is affecting where the sperm whales go at different times of the year."
Although old records and surveys indicate the Ross Sea was a hotspot for sperm whales, Pinkerton said people stationed in research and fishing vessels in the area rarely reported seeing them.
"We're really interested in finding out why we don't see sightings of those sperm whales but we do think that they're there," he said.
"We're really excited about trying to look at that data and trying to put another piece of the puzzle and trying to work out the life cycle and the occurrence of these sperm whales."
Sperm whales – particularly the large males who feed on toothfish in the Ross Sea - were targeted by the whaling industry in the 19th and 20th centuries, which saw more than 70 per cent of their population wiped out. They are now classified as vulnerable.
Pinkerton said the species was "cryptic".
"We don't really know their annual cycle - where their populations are concentrated and how different groups of whales interact."
Scientists did know the whales ate a lot of toothfish, and could dive down to 3000m to find them.
"The abundance of toothfish on the Ross Sea slope has reduced because of fishing and is set to reduce further in the future," he said.
"We want to know if that's affected sperm whales there."
"To do that, we need to see where they are now and work out how to monitor changes in the future."
The research vessel Tangaroa will leave Wellington on January 8, and return on February 17.