Disease-carrying Ice Floats

Steller sea lions on sea ice

NOAA Fisheries, Polar Ecosystems Program, AFSC

Phocine distemper virus (PDV)—a potentially fatal marine mammal disease in the Morbillivirus genus that affects the respiratory and nervous systems—can spread within and between species through coughing or direct contact when animals are in close proximity in the water or on land. PDV had previously been found only in the North Atlantic Ocean but has recently emerged in multiple species in the Pacific Ocean. A new study has linked the spread of PDV to melting sea ice, facilitating cross-species interactions.

A team of researchers, led by Tracey Goldstein at the University of California Davis, tracked PDV exposure and infection in 2,695 Pacific seals, sea lions, and sea otters from 2001 to 2016. Analysis of PDV strains sampled from live and dead animals, combined with satellite tag data to estimate species’ locations and movements, enabled the researchers to track the geographic and species-to-species spread of PDV over time.

Previous studies reported outbreaks of PDV in Atlantic harbor seals (Phoca vitulina) in 1988 and 2002. In 2003, Goldstein and her colleagues detected PDV in Pacific Steller sea lions (Eumetopias jubatus) for the first time. Using satellite imagery data, the researchers found that a record reduction in Arctic sea ice in 2003 resulted in a new temporary water route between the Atlantic and Pacific oceans, along the Russian coast. Their study suggests that harp seals (Pagophilus groenlandicus), which live in the Arctic and North Atlantic Oceans, gave PDV to Atlantic harbor seals or gray seals (Halichoerus grypus), which then carried the virus along the Russian coast to the Pacific Ocean. From there, PDV spread to Steller sea lion pups and then, in 2004, to Northern sea otters (Enhydra lutris kenyoni). Sea ice melt opened this Atlantic-to-Pacific water route again in 2008, preceding another peak in PDV exposure and infection in 2009 in Pacific Steller sea lions, with 34 percent of sampled animals exposed to the virus.

As sea ice continues to recede, Goldstein says she and her colleagues plan to keep monitoring these populations both for PDV and other health issues in order to track the well-being of the animals and the possible effects on human populations that rely on them. (Nature Scientific Reports)