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Mystery disease showing up in Bering Sea ribbon seals

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  • Updated: May 31, 2016
  • Published May 10, 2016

Five years after a mysterious and sometimes fatal disease struck Arctic Alaska ringed seals, causing them to lose their fur or develop bleeding lesions, there are signs of the disorder or something similar to it among a different species of ice-dwelling seals.

Federal scientists who just completed a survey of ice seals in the Bering Sea found several ribbon seals with bald patches, including one that was almost completely bald.

Of the 10 ribbon seals found, sampled and tagged during the National Oceanic and Atmospheric Administration research cruise through the edge of the sea ice, all seven adults and subadults in the group showed symptoms similar to those affecting ringed seals in 2011 and 2012. Aside from the animal that was nearly bald, five had patchy baldness and one, though it had all its fur, had lesions and pustules on its body and flippers, said Michael Cameron, chief scientist for the survey and a biologist with the National Marine Mammal Laboratory at NOAA's Alaska Fisheries Science Center.

All seemed healthy except for the nearly bald seal, Cameron said. That animal was lethargic, opting to stay still even when scientists were right next to it, he said. But later on, after it was captured, measured and otherwise studied, the bald seal went back into the water and was swimming around, he said.

Conditions for northern Alaska seals were much more serious in 2011, when scores were found sick or dead, with bald spots in their fur and bleeding lesions on their bodies. Most of those affected at the time were ringed seals, though other seals were also affected. There were sick spotted and bearded seals, according to reports. There was at least one ribbon seal found then that had the mystery illness, said Peter Boveng, director of the National Marine Mammal Laboratory's Polar Ecosystems Program.

NOAA declared the situation an "unusual mortality event," a designation under the Marine Mammal Protection Act that warrants special scientific investigation. A related unusual mortality event was declared by the U.S. Fish and Wildlife Service for walruses, some of which were also appearing with the bleeding sores on their bodies. The investigation into the seal illnesses and deaths continues, though the walrus investigation was closed last year. Since 2014, there have been very few sightings of ice seals as sick as those found in 2011, though some cases of patchy baldness among otherwise healthy seals have been reported, said Maggie Mooney-Seus, a spokeswoman for NOAA's Alaska Fisheries Science Center.

The cause of the illness that emerged in 2011 is still unknown; radiation poisoning, harmful algal blooms and bacterial infections are among the possible culprits that have been investigated."There hasn't been a definitive diagnosis yet," Boveng said.

Also unknown is whether the scientists' encounters last month with ribbon seals show signs of a new outbreak, lingering effects of the old event or something different.

Boveng said researchers are fairly certain that the disease wasn't present before 2006 and signs of patchy baldness among ribbon seals were not evident in research cruises taken between 2006 and 2010. There were some sightings in 2014 though, Boveng said.

Ribbon seals are named for the ribbon-like patterns on their black-and-white fur, which do not develop until the animals are 4 years old. Ribbon seal pups are pure white.

Ribbon seals have another distinguishing feature – an internal air sac above their ribs. They are the only seal species with such an air sac, according to NOAA.

Citing the disappearance of summer and fall sea ice that the animals use and other habitat disturbances, environmentalists in 2007 petitioned NOAA to grant Endangered Species Act protections for ribbon seals. The effort was unsuccessful. NOAA ultimately determined in 2013 that there was not enough evidence to justify a listing.

If there is some kind of disease in the ribbon seal population, it may have gone unnoticed for a while.

While ringed seals, bearded seals and spotted seals are hunted by local indigenous people -- and therefore much monitored -- subsistence hunts of ribbon seals are much smaller, according to NOAA. That means local hunters had less opportunity to observe ribbon seals and report any problems they might be having.

The patchy baldness is not obvious, Cameron said. "You basically have to have the animal in hand to see that," he said. "It would be difficult to recognize from too far away."

It is also possible that the ribbon seals are survivors of the past outbreak, showing some lingering symptoms but not serious ill effects, the NOAA scientists said.

The seal survey, a four-week campaign carried out in April, targeted all four types of ice seal. Scientists scooped up the animals into large nets, weighed and measured them, took blood samples and some biopsies, fitted them with tracking devices and let them go. Those surveys started in 2006, though scientists skipped some of the years, Boveng said.

For those investigating seals, ribbon seals happened to be the easiest targets, thanks to a behavioral quirk that causes them to linger on ice floes a little longer than other seals do, Boveng said. "Frankly, ribbon seals are the easiest on for us to catch," he said.

The nearly annual seal surveys are part of a wider multiagency program counting and assessing marine mammals on both sides of the Bering Strait.

An aerial survey employing infrared and thermal devices to detect seals and polar bears in the ice is now underway. Scientists from the Russian State Research and Design Institute for the Fishing Fleet are cooperating in that effort.

Correction: In an earlier version of this story, Peter Boveng was quoted saying signs of the disease were not noticed in ribbon seals prior to 2016. He actually said the signs were not present prior to 2006.

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