When the first Polynesian settlers arrived on the shores of New Zealand somewhere between 1200 and 1300 CE, they would have been met by the vision of thousands of prehistoric sealions and southern elephant seals lining the sandy shores of a land untouched by humans.

It’s an image hard to imagine today, particularly as – over the centuries – the elephant seal has become a species that has simply fallen outside of the New Zealand biological heritage, forced southwards, new research has shown, by climate change.

Yet, according to a new study from scientists at Griffith University, it’s only some 400 years ago that New Zealand beaches were once “heaving” with these colossal, southern elephant seals. 

These findings have prompted researchers to liken southern elephant seals to the ‘canary in the coal mine’ for the Southern Ocean, offering insight into how the ecosystem may react to future climate change and human impact.

Joint senior author Associate Professor Nic Rawlence, director of the Otago Palaeogenetics Laboratory at Griffith University, said: “At the time of human arrival in New Zealand, you would be hard pressed to find room on the beaches, with fur seals on the rocky headlands, prehistoric sealions, and elephant seals on the sand… and lots of penguins.”

Led by postgraduate students Andrew Berg of the University of Sydney, and Otago’s Megan Askew, the study – undertaken by a group of international researchers – has recently been published in the journal Global Change Biology. 

To conduct their study, the team used palaeogenetic techniques – a process that involves extracting and analysing DNA from ancient biological materials like bones, teeth, and sediments – on specimens dating back thousands of years from New Zealand, Tasmania, and Antarctica to show that southern elephant seals used to be spread across the entire Southern Ocean.

However, it’s according to joint senior author, Dr Mark de Bruyn of Griffith University’s Australian Research Centre for Human Evolution, that their whereabouts were heavily impacted by climate change and humans over a short evolutionary period.

“The Ice Ages would have rapidly increased the amount of sea ice surrounding Antarctica, forcing elephant seals to retreat to multiple refugia in South Africa, Australia, New Zealand, and South America, before they expanded back out as the climate warmed, including temporarily to the Antarctic mainland.

“However, indigenous subsistence hunting and European industrial sealing once again resulted in the contraction of their range, this time to the deep Southern Ocean with their extirpation from Australia and New Zealand.”

Associate Professor Rawlence said that knowing how elephant seals responded to these changes would provide insights into how they – and the Southern Ocean ecosystem which New Zealand and Australia were a part of – may be impacted in the future.

It’s no secret that the Southern Ocean is currently warming faster than other parts of the planet. How this region’s endemic biodiversity will respond to such changes can be illustrated by studying the events of the past, and doing so through the genetic analyses of “time-series data sets” – sign posts from the past, including historic and fossil remains.

Polar and sub-polar species, like the southern elephant seal, are particularly vulnerable to the impacts of global climate change because of their specialised habitats and the rapid warming experienced across them.

The largest pinniped and largest non-cetacean marine mammal, the southern elephant seal is an apex predator that consumes massive amounts of biomass to maintain its bulk during a nine-month foraging period. Yet, this species inhabits a region that is undergoing rapid climate change – the sub-Antarctic and Southern Ocean.

“Their dynamic evolutionary history, plus climate change and human impact, strongly suggest that unless measures are taken to mitigate the effects of human-driven climate change and marine ecosystem deterioration, elephant seals and the Southern Ocean ecosystem are in for a rough ride into the future,” said Rawlence.

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