Northern elephant seals sleep in the deep to avoid predators

[Judi Lynn]

Published
8 hours ago



JESSICA KENDALL-BAR

Elephant seals are known for sleeping for long periods when they are on land


By Victoria Gill
Science correspondent, BBC News

Northern elephant seals sleep while drifting hundreds of metres below the sea surface - at depths where their predators do not usually lurk. US researchers tracked the animals, recording their brain activity as the seals swam for thousands of kilometres.

The mammals, which reach depths of up to 2,500ft (760m), sleep for only two hours per day in what the researchers describe as "nap-like sleeping dives". The findings are published in the journal Science.

University of California Santa Cruz researcher Jessica Kendall-Bar and colleagues developed a non-invasive stick-on tag to track and simultaneously monitor the brain activity of wild northern elephant seals off the coast of California.

They followed eight wild mammals on their foraging trips, which lasted about seven months and spanned more than 6,200 miles. They recorded the animals' brain activity, heart rate, movement and body position

More:
https://www.bbc.com/news/science-environment-65338500

[Duppers]

1. Wonder how their oxygen lasts that long?

[NNadir]

2. The full article in Science gives a reference that discusses this topic.

It's reference 13 in the full paper, which is here: Kendall-Bar, Jessica M.; Williams, Terrie M.; Mukherji, Ritika; Lozano, Daniel A.; Pitman, Julie K.; Holser, Rachel R.; Keates, Theresa; Beltran, Roxanne S.; Robinson, Patrick W.; Crocker, Daniel E.; Adachi, Taiki; Lyamin, Oleg I.; Vyssotski, Alexei L.; Costa, Daniel P.; Brain activity of diving seals reveals short sleep cycles at depth, Science, 260-265, 380, 6642, (2023)

Reference 13:

M. J. Weise, D. P. Costa, Total body oxygen stores and physiological diving capacity of California sea lions as a function of sex and age. J. Exp. Biol. 210, 278–289 (2007).

The latter paper is fully open sourced, but basically the idea is that phocids (true seals), the order to which Elephant Seals (Mirounga angustirostris) belong, store significant quantities of their oxygen in their muscle tissue, in myoglobulin, as well as in hemoglobulin in their blood. Their ability to do so apparently changes with age.

In sleep, they are in a reduced metabolic state, probably with lower body temperatures.