Genetically Unique Population of Blue Whales Identified in New Zealand
A population of pygmy blue whales (Balaenoptera musculus brevicauda) that inhabits the waters between the North and South islands of New Zealand has been shown to be genetically distinct from other populations around the globe, according to new research.
The study, published in the Endangered Species Research Journal, was led by Dr Leigh Torres of the Marine Mammal Institute at Oregon State University, who has been studying the blue whale populations of the southern oceans since 2011, after reports of regular sightings around the South Taranaki Bight, a large bay on the southern coast of New Zealand's North Island.
Further studies showed the presence in the area of large blooms of krill on which blue whales are known to feed, however, Dr Torres' proposal that the sightings of whales in the area might be a unique aggregation was initially met by scepticism from both other scientists and the New Zealand's offshore mining industries. Several oil and gas rigs are located within the South Taranaki Bight, and New Zealand's government has recently issued permits for the mining of 'ironsand' from the sea floor – a source material for New Zealand's steel industry.
The presence of blue whales in the area was previously held to be migratory, hence the new study is of particular significance to blue whale conservation, as the species is currently listed as 'endangered' on the IUCN red list.
During 2016 and 2017, Dr Torres and her research assistant Dawn Barlow conducted extensive surveys in the region using acoustic data, identification photographs and genetic samples from biopsies. Together with historical sighting reports, Torres and Barlow identified a total of 151 individual blue whales between 2004 and 2017, suggesting there may be over 700 animals within the local population. Nine individual whales were recorded over multiple years, and no matches were made to blue whales previously sighted in Australian or Antarctic waters. The results suggested a 'high degree of isolation' of the New Zealand population.
'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 Torres, a 'When we conducted biopsies of individual whales, we also discovered that they are genetically distinct from other blue whale populations.'
'There is no doubt that New Zealand blue whales are genetically distinct, but we're still not certain about how many of them there are,' said Barlow. 'We have generated a minimum abundance estimate of 718, and we also were able to document eight individuals that we re-sighted in multiple years in New Zealand waters, including one whale seen in three of the four years with a different calf each time, and many others we saw at least once.'
Blue whale populations were decimated by the whaling industry until they gained protected status in 1966. Dr Torres said the OSU researchers are 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 minimize impacts from industry.'