Phocine distemper virus (PDV) has been common in the northern Atlantic ocean for decades but as a result of melting Arctic sea ice it has now appeared among marine mammals in the northern Pacific ocean too.
The 15-year study which tracked the animals via satellite found PDV, which can kill some species, was most common in years when so much Arctic ice melted it became possible for mammals to move freely from the Atlantic to Pacific regions.
Steadily rising global temperatures due to climate change have meant more and more sea ice is melting around the Arctic, opening up sea lanes which for thousands of years have been impassable.
Between 1979 and 2018, Arctic sea ice declined on average 12.8 per cent each decade, according to the Intergovernmental Panel on Climate Change (IPCC).
“These sea ice changes in September are likely unprecedented for at least 1,000 years,” the IPCC said in a report published in September.
The scientists said a severe spike in PDV in 2003 and 2004 among marine mammals in the northern Pacific was connected to a record ice melt in August 2002.
Testing showed about 30 per cent of Stellar sea lions in the northern Pacific Ocean were infected with the disease, which had previously been mostly confined to Atlantic populations.
PDV did not peak again in the Pacific until 2009, which was also just one year after widespread melting in 2008 that created open water passage routes.
“The loss of sea ice is leading marine wildlife to seek and forage in new habitats and removing that physical barrier, allowing for new pathways for them to move,” one of the study’s authors Dr Tracey Goldstein, from the University of California, Davis, told the BBC.
“As animals move and come in contact with other species, they carry opportunities to introduce and transmit new infectious disease, with potentially devastating impacts.”
Symptoms of PDV include laboured breathing, fevers and attacks on the nervous system. It was first identified in the late 1980s after unprecedented epidemics swept through populations of seals and sea lions, beginning with landlocked seals in Lake Baikal in Siberia.
This first outbreak killed about 18,000 harbour seals in the North and Baltic Seas. Another epidemic in 2002 in the North Sea is believed to have wiped out more than half of the seal population in the region.