A rare whale species that was nearly hunted to extinction have been found to hang around Southern Ocean shores more often and longer than first thought.
The discoveries were made using technology that could be crucial to helping the southern right whale's recovery.
Once abundant around New Zealand coasts, the ocean giants are now mainly found at their remote breeding ground, the Auckland Islands, some 460km south of Bluff.
It was estimated there were 30,000 before whaling in throughout the 1800s devastated their population, which had returned from the brink to around 2000 individuals today.
Scientists had little idea how long the whales hung around their subantarctic stronghold, so carried out a year-long study that dropped in on their songs using acoustic monitors.
They found they could hear their calls in every month except January, and the calls peaked during the winter months when the whales move near the shore to calve.
The most common calls were upcalls, a deep, rising "whoop" that lasted about a second, which were thought be a type of "contact call" - a way of letting other whales know who is around.
Otago University marine conservation biologist Professor Steve Dawson said there was little reliable information on how their vocalisations varied throughout the year, how they used different types of vocalisations, and the rate at which they called.
"These data are important for understanding the ecology of this toanga species," Dawson said.
"We also wanted to test an automated call detector, which, if successful, could be very useful in monitoring right whale presence."
Dawson and colleagues installed an autonomous sound recorder, programmed to record for 3.75 minutes every 30 minutes, in Port Ross, the key inlet used by breeding right whales.
The recorder had sufficient battery capacity and memory to record for just over 300 days.
Otago University's Dr Trudi Webster analysed the sounds to classify them into different call types, and also tested an automated call detector developed to detect upcalls made by North Atlantic right whales.
"We now know when the whales are present at the Auckland Islands - approximately May to November," Dawson said.
"We know which call types are used most often – upcalls - and therefore which calls are best for monitoring right whale presence."
This would be important for tracking the population's recovery.
"We have proven that the approach works really well in areas that are difficult to get to, and provides ability to document whale activity, over long periods, night and day, and in weather conditions that would shut down visual observation," Dawson said.
"A fully automated detector, rather than recorder, for New Zealand right whales is some time away, but our work to date is a significant step towards the development of this tool.
"Being able to know when right whales are present in the inshore waters of New Zealand would be of very great value as the species recovers to its previous haunts."
The study follows other new research that suggested the species might be rediscovering ancient migratory pathways to New Zealand through information historically passed from mother to young.
That could spell more encounters like the traffic-stopping visit one southern right whale made to Wellington last July, earning it the name Matariki.