Study links Alaska seals’ waning health to warming Arctic

A mom and baby seal on some ice
Spotted seal mother and pup in the Bering Sea. (NOAA)

As global temperature rise warms the coldest parts of the world, scientists are watching for changes in 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: How fat the seals were.

Boveng said they found 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 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.”

Both of ribbon and spotted seals tend to gather on the edge of the sea ice to hunt for food and raise their young. But sea ice extent has drastically diminished over the past decade, losing 18,000 square miles a year on average. Boveng said that could impact how much seal mothers can 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)

The study ranged 2007 to 2018, and during that time Boveng said two species of seals experienced two unusual mortality events — an unexpected, rapid decline in population.
During the first event, the seals acted lazier, with many showing hair loss and sores. But Boveng said there was no evidence linking those things to a loss of food or a warming climate.

The second event saw more evidence the decline was food-related.

“So this second [mortality event], 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 — about 10% of their weight. Boveng said the decrease is tied to a heat wave in Southwest Alaska between 2014 and 2016. He said 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 said scientists forecast warmer Arctic conditions will become normal. He anticipates changes to the seals’ bodies will be much clearer as time goes on.