The gigantic marine mammals are genetically distinct from whales found in the neighbouring Pacific and Antarctic Oceans, suggesting they are a separate group that lives permanently in the region.
While they are not as large as their Antarctic cousins, the New Zealand population can still reach lengths of around 22 metres.
Their discovery is being hailed as significant because the whales’ home in the South Taranaki Bight is also the setting for several oil and gas rigs and is set to be targeted by seafloor mining operations.
Though blue whales have long been listed as a migrant species in the region, Dr Leigh Torres of the Marine Mammal Institute at Oregon State University was the first to suggest it might be home to a resident population.
This was confirmed when she began conducting expeditions in the South Taranaki Bight to look for signs that it was a blue whale hotspot.
On a 10-day research expedition conducted in 2014, Dr Torres and her colleagues identified 50 blue whales, but they needed to ascertain whether these individuals were migrating from nearby waters or a permanent fixture.
Over the next three years the team conducted longer term studies in which they tried to establish the number of whales and how they were distributed around the region.
“We had five hydrophones deployed for two years in the South Taranaki Bight and we never heard any Australian blue whale calls – just the local New Zealand population,” said Dr Torres. “When we conducted biopsies of individual whales, we also discovered that they are genetically distinct from other blue whale populations.”
The findings were published in the journal Endangered Species Research.
Having established this new population, the scientists now want to determine exactly how many of them there are inhabiting the large bay of South Taranaki Bight. Their current minimum estimate is 718.
“While we have gained a great amount of information about blue whales in New Zealand over the past few years, we continue to analyse our data and do more research to address other knowledge gaps,” Dr Torres said.
In light of the planned industrial work in the region, Dr Torres and her colleagues intend to present their findings to political and industry leaders – including representatives from the whaling industry – this summer.
The team is now “working closely with resource managers in New Zealand to help them understand what we do and don’t know about this New Zealand blue whale population so they can apply best management practices to minimise impacts from industry”.