Now University of Otago researchers have discovered southern elephant seals may be the equivalent warning system for the Southern Ocean, offering an insight into how the ecosystem may react to future climate change and human impacts.
As human-driven climate change continues, the Southern Ocean is expected to continue warming, causing further habitat loss for species that depend on sea ice and are affected by shifts in the availability of prey.
Joint senior author and Otago Palaeogenetics Laboratory director Associate Prof Nic Rawlence said the elephant seals’ history offered a window into how marine mammals might respond to these changes, and also served as a warning: human impacts, coupled with environmental pressures, could lead to swift, sometimes irreversible declines.
Assoc Prof Rawlence said elephant seals now only inhabited the subantarctic islands and South America.
But in the past, they were prominent on New Zealand, Australian and South African beaches as well.
"If you time-travelled back to the time of Polynesian arrival, you would have either tripped over something or stood on something on the beach in the first five minutes.
"If you think of beaches around Dunedin, say St Clair and St Kilda, the sand would have been covered in penguins, sea lions and elephant seals, and the headlands would have all been covered in fur seals."
Joint senior author and Griffith University molecular ecologist Dr Mark de Bruyn said their whereabouts was 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," he said.
"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."
Assoc Prof Rawlence said the elephant seal’s evolutionary history showed they were rapidly responding to climate change and human impacts.
At the moment, elephant seals on Macquarie Island were having to travel increasing distances from their breeding grounds on the island to their food sources because of the rapidly warming Southern Ocean temperatures.
And the population was not doing well, he said.
"Going back to the canary in the coal mine ... in this case, the elephant seals are an apex predator of the Southern Ocean and they are responding to what climate change and human impact is doing to their ecosystem."
He said knowing how elephant seals responded to these changes would provide insights into how they, and the Southern Ocean ecosystem, might be impacted in the future.
"Their dynamic evolutionary history, plus climate change and human impact, strongly suggests 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.
"Essentially, they’re showing that we still have a lot of work to do to protect their breeding grounds, making sure that runaway climate change isn’t impacting the ecosystem, and protecting their food resources.
"Currently, what we are seeing happening with elephant seals should be that warning the canary is giving us, and we need to heed it."
