New Zealand waters provide an important migratory route for the biggest animal to ever exist, the Antarctic blue whale,
according to a study led by a University of Auckland scientist.
Hydrophones, or underwater microphones, anchored at the bottom of the ocean around central New Zealand recorded the
whales’ low-frequency calls, which are loud enough to be heard across hundreds of kilometers, to monitor their
locations.
The giant creatures travelled a route that runs through the South Taranaki Bight, an area off the west coast of the
North Island and above the South Island, the study showed.
Antarctic blue whale detections were greatest in the South Taranaki Bight during winter, when the whales were
northbound, heading for warmer waters to breed, before peaking again in spring, when the whales were returning to the
Antarctic to feed, the research showed. Antarctic blue whales were also detected to a lesser extent off the east coast
of central New Zealand, offshore from Kaikōura and the Wairarapa.
The study, just published in the journal Frontiers of Marine Science, was a joint effort by the University of Auckland and the National Institute for Water and Atmospheric Research (NIWA),
with collaborators from Texas A University in the United States and acoustic monitoring firm JASCO Applied Sciences (Australia).
“This research shows that New Zealand waters provide an important habitat for these incredible creatures,” said Dr
Victoria Warren, of the Institute of Marine Science, who led the research. “These animals are critically endangered, and
we need to do everything we can to protect them.”
Antarctic blue whales reach up to 30 meters in length and 200 tons in weight, with hearts the size of small cars. They
are bigger than the biggest dinosaurs ever were, but hunted to the brink of extinction last century. The United Nations
estimated a population of 3,000 in 2018 – compared with a peak of as many as 200,000 whales prior to commercial whaling.
The acoustic data pointed to the possibility that Antarctic blue whales may breed in New Zealand waters, since their
calls were heard during the breeding season of September and October, but the evidence wasn’t conclusive.
New Zealanders may on rare occasion spot an Antarctic blue whale, but the creatures are notoriously difficult to
distinguish – visually, at least – from the somewhat smaller, but still huge, pygmy blue whales.
To get a clearer picture of the habits of both types of blue whale, scientists eavesdropped via microphones deployed at
depths ranging from 100 to 1,500 metres. While identifying the sub-species visually can be difficult, it’s
straightforward via sound.
The data revealed that pygmy blue whales seem to congregate in the South Taranaki Bight, especially between March and
May, which supports other research findings and highlights that this area is very important for both types of blue
whale.
Underwater microphones were deployed in 2016 at four locations around central New Zealand -- the South Taranaki Bight,
Cook Strait, and off the coasts of Kaikōura and Wairarapa – and in 2017 at three of those locations.
Over 106.5 days, a total of 20,751 blue whale calls were detected, with both of the sub-species turning up at all of the
locations.
``This research really illustrated the value of long-term deployments of underwater microphones, for monitoring rare and
hard-to-observe animals such as large migratory whales,” said Associate Professor Rochelle Constantine, one of the
co-authors of the paper.
Potential threats to whales range from collisions with ships to plastic pollution and anthropogenic noise from sources
such as oil and gas exploration, which disrupts their communication. Warming and changes in acidification levels of the
ocean as a result of climate change have the potential to alter marine ecosystems faster than whales can adapt.