Sea ice in the Arctic melts every summer and refreezes in the winter, but the melting has been outpacing the refreezing for many years. According to NASA, Arctic sea ice now declines at a rate of 12.85 percent every ten years. That reduction seems to now be impacting marine mammals; researchers have linked the decline to the emergence of a virus called phocine distemper virus (PDV) that infects North Pacific marine mammals. The PDV pathogen killed thousands of harbor seals in the North Atlantic in 2002, and was found in northern sea otters that reside in Alaska in 2004.
Scientists at the University of California, Davis wanted to know more about how the virus reached Alaska, and conducted a study using data collected from 2001 to 2016, which has now been published in Scientific Reports. They hypothesized that as historic sea ice has been dramatically reshaped, it's allowed the virus to move into the Northern Pacific.
"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," said the corresponding author of the study Tracey Goldstein, associate director of the One Health Institute at the UC Davis School of Veterinary Medicine. "As animals move and come in contact with other species, they carry opportunities to introduce and transmit new infectious disease, with potentially devastating impacts."
The scientists found that about 30 percent of some sea mammals tested positive for the virus in 2003 and 2004. The virus then began to decline before peaking again in 2009. Satellite images showed that there were open water routes were present in 2002, 2005, and 2008, and suggested that infected animals can carry PDV over long distances.
The virus has varied impacts on different species. Atlantic harbor seals are highly susceptible, while grey seals, for example, don't suffer the same population losses.
"As sea ice continues its melting trend, the opportunities for this virus and other pathogens to cross between North Atlantic and North Pacific marine mammals may become more common," said the first author of the study Elizabeth VanWormer, who conducted this research as a UC Davis postdoctoral fellow and is now an assistant professor at the University of Nebraska, Lincoln. "This study highlights the need to understand PDV transmission and the potential for outbreaks in sensitive species within this rapidly changing environment."