Quirks & Quarks

Elephant seals buoyantly navigate 'lightscape of fear' in long sea migrations

Elephant seals take fewer risks out in the open ocean the fatter they get

Elephant seals take fewer risks out in the open ocean the fatter they get

The tags on this female elephant seal record data throughout its seven-month foraging migration. (Dan Costa)

Every year, elephant seals undertake a seven-month-long migration into the open sea, and must carefully navigate the treacherous waters to make sure they eat enough and don't get eaten. 

Roxanne Beltran, an assistant professor of ecology and evolutionary biology at the University of California Santa Cruz, wanted to figure out how the female elephant seal's body condition affected the risks they were willing to take.

Their risk in the open ocean varies with light, what Beltran calls "lightscapes of fear."

UCSC biologist Roxanne Beltran (foreground) and other researchers prepare to outfit a female elephant seal with a satellite tag and time-depth recorder at Año Nuevo Reserve. (Dan Costa)

White sharks and killer whales use light to hunt, so elephant seals want to avoid areas closer to the ocean surface, especially during daytime.

The elephant seals spend a great deal of time eating, but they also need to rest — something they do a few hundred metres below the surface, in the safe dark depths of the ocean. 

Most of their prey tend to spend the daylight hours deeper in the ocean, where it's less efficient for the elephant seals to hunt because they need to be close to the surface to breathe air.

According to Beltran's findings, which were published in the journal Science Advances, the elephant seals took more risks by prioritizing feeding earlier in their journey, but as they gained fat, they shifted their strategy to prioritize rest in the safety of darkness.

Produced and written by Sonya Buyting