Marine mammals living in the North Atlantic Ocean and the North Pacific Ocean are not supposed to meet. Historically barred by solid Arctic ice, they were long kept separate. Not any more. As sea ice in the Arctic Ocean diminishes (dropping to the second-lowest level ever in 2019), new channels between the two oceans are opening up, and for some species there are dangerous consequences.
Tracey Goldstein, a professor at UC Davis School of Veterinary Medicine, has been investing these consequences for the last 15 years. It began in 2004 when researchers discovered the Phocine distemper virus (PDV) in sea otters in the North Pacific. This was a surprise. PDV was already known as a deadly disease, having drastically impacted European harbour seal populations following an outbreak in 2002 – but these animals lived in the North Atlantic.
‘We were trying to figure out how was it that the virus could get to Alaska,’ says Goldstein. ‘We initially started looking at the overlap of seals, wondering if they could suddenly come in contact with each other and then move the virus down. When we looked at the ice data, we found that the only way that could happen was if there was an opening in the ice.’
Over the next 15 years, Goldstein and fellow researchers investigated this theory using satellite images of sea ice and by collecting samples from 2,530 live and 165 dead seal, sea lion and sea otter species in the North Pacific. They were able to link increased levels of PDV exposure or infection in the North Pacific with the presence of two new open water routes between Russia and Alaska connecting the Atlantic and Pacific oceans. They found that widespread exposure to the infection peaked twice, in 2003 and 2009. Both outbreaks were preceded by record-low sea ice.
On the plus side, the PDV virus does not yet appear to have the same devastating effect on North Pacific marine species as it does on harbour seals in the Atlantic. Nevertheless, with open water routes along the northern Russian coast having occurred every August or September since 2008, this transmission could be the first of many. It could also trigger consequences as yet unknown.
‘Things are interconnected. And as ice retreats, seals have to change their behaviour, haul out in further places or feed in different places,’ says Goldstein. ‘That will, over time, affect the health of the people living in Alaska who rely on them. What’s happening in the environment will affect the animals and then in turn also affect the people. I think we really can’t imagine yet what all those consequences are going to be.’
Get the best of Geographical delivered straight to your inbox by signing up to our weekly newsletter and get a free collection of eBooks!