Study connects physical decline of Alaska seals to warming Arctic

Spotted seal mother and pup in the Bering Sea. (NOAA Fisheries photo)

As global temperatures rise and warm the coldest parts of the world, scientists are watching for changes to species that live there. A new study has found evidence connecting the rapid warming of the region with a physical decline in three species of Alaska seals.

For 12 years, researcher Peter Boveng with the National Oceanic and Atmospheric Administration led a team that monitored ribbon and spotted seals in the Bering Sea. They were specifically monitoring body condition, or how fat the seals were. Boveng says what they found was the youngest seals were getting smaller.

“The fatness of the pups, the young of the year, declined on average over that time period,” Boveng said.

Boveng says this is one of the first major studies that shows evidence of a noticeable change in the seals’ body condition related to global warming.

“There hadn’t been, up until now, really much of any documentation of impacts that we think are climate related,” Boveng said.

Both of these species of seal tend to gather on the edge of the sea ice to hunt for food and raise their young. However, sea ice extent has drastically diminished over the past decade, with an average loss of just over 18,000 square miles a year. Boveng says that could impact how much seal mothers are able to forage.

“The mothers, maybe, were not finding as much food in the period prior to the birth of their pups, when they were pregnant,” Boveng said. “And also maybe not having as much fat or finding as much food during the nursing period.”

NOAA Fisheries scientists approach a ribbon seal. (NOAA Fisheries photo)

Between 2007 and 2018, the time period of the study, Boveng says that the two species of seals experienced two unusual mortality events, or an unexpected rapid decline in population. During the first event, the seals acted more lazy, with many showing sores on their bodies and loss of hair. Boveng says there was no evidence linking those things to a loss of food or a warming climate. He says the second however, saw more evidence that the decline was food-related.

“So this second UME which occurred right in the years of record low ice extent in the Bering Sea, really seemed to line up with the things we were seeing,” Boveng said.

A related study of harbor seals in the Aleutians found a similar decline over a three-year period, with an average decrease of 13 pounds per year — that’s about 10% of their weight. Boveng says that decrease is tied to a heat wave in Southwest Alaska between 2014 and 2016. He says it’s clear the dramatic decline in weight hadn’t been going on for long.

“The decline in harbor seal body condition over that period was pretty rapid,” Boveng said. “Something like that wouldn’t be something that had been going on for a long time, because they would’ve just wasted away.”

Looking to the future, Boveng says that scientists forecast warmer Arctic conditions will become more normal, and he anticipates that changes to seal bodies will be much clearer as time goes on.

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