How Harbor Seals Choose Their Perfect Ride

Harbor seals off the coast of Alaska pick the icebergs on which they bask depending on the season, according to new research presented today at the American Geophysical Union’s annual meeting.

The research focused on harbor seals in Alaska’s Glacier Bay National Park, where the Johns Hopkins glacier is advancing—one of the few on Earth doing so, according to an AGU release. Due to the circumstances of its advancement, the glacier is not shedding many icebergs into a fjord, reducing the seals’ habitat. The recent research investigated the sorts of icebergs the harbor seals (Phoca vitulina) elect to chill on (no pun intended) over the course of the year.

“Icebergs are found throughout the fjord in regions of fast flow, within eddies, and close to the glacier,” said Lynn Kaluzienski, a researcher at the University of Alaska Southeast and lead author of the study, in the release. “We wanted to understand which of these areas seals were using and how this habitat is changing in response to advances at the glacier front and reduction in iceberg numbers.” 

The researchers found that seals tended to set up shop on slower-moving icebergs during the pupping season (June) and faster-moving bergs during molting season (August). The team classified slower-moving icebergs as those moving at a pace of 7 to 8 inches (0.2 meters) per second. During molting season, the seals tended to be on bergs closer to fast-moving water made up of ocean currents and glacial runoff, called the plume. The plume surfaces plankton and fish, according to the AGU release, offering up a feast for the seals.

The team posits that the slower bergs offer more stability to adult seals tending to their pups in the early summer. During molting season that stability is less important, and the faster bergs offer opportunities to eat with ease.

“Our work provides a direct link between a glacier’s advance and seals’ distribution and behavior,” Kaluzienski said. “Interdisciplinary studies like this one coupled with long-term monitoring campaigns will be important to understand how climate change will influence tidewater glacier fjord ecosystems in the future.” 

Climate change could drastically change the seals’ environments; an AI-driven analysis of 10 climate models released today found that 34 regions defined by the International Panel on Climate Change (IPCC) have a 50/50 chance of warming by 3.6 degrees Fahrenheit (2 degrees Celsius) compared to preindustrial levels.

It’s been a busy year for seals more generally. In February, a male elephant seal caused a stir when it saved a drowning pup, shoving back to shore with its head. Not all the news was so wonderful: In July, nine seals off the coast of South Africa tested positive for rabies, after months of reports of seals attacking humans.

The seals off Alaska are having a chiller go of it than their South African compatriots. The reduction in iceberg numbers isn’t good for them, but at least they don’t have rabies. There’s always a silver lining!