Dear Readers, I have always had a soft spot for elephant seals – they look like characters from a children’s book, they don’t put up with any old nonsense and the pups could not be cuter if they tried. I met them ‘in the flesh’ on an island off Baja California which used to be an old canning station, and the elephant seals were hauled out on the jetty and beach. They watched us as we wandered around (keeping a respectful distance) and would occasionally sigh deeply, as if it was all too much effort.
Elephant seals dive very deep to capture their prey (skate, sharks, octopuses and other deepwater denizens) – the record for a Northern Elephant Seal is over 1700 metres. However, I had no idea that the slept underwater, or how that worked. Well, Californian scientist Jessica Kendall-Barr and her team decided to find out.First, they found some relatively amenable female elephant seals who could be somehow persuaded to wear a cap for a few days that measured their brain activity and heart rate – the caps were attached with a glue which would wear off in less than a week. I notice that they decided not to wrestle with the males who, though looking like enormous docile blobs when unmolested can rear up to almost six feet high when cross, which they often are.
Five of the seals spent all their time on the beach or in shallow water, but three of them headed off to the deep ocean, which is where elephant seals spend most of their time when not breeding. Unsurprisingly, the seals don’t sleep much when they’re at sea – they usually nap for ten minutes at a time, and sleep for less than two hours a day (compared to ten hours when they’re on land). But what is astonishing is what happens when they do nap. At about 100 metres down, the seals go into slow-wave sleep and start to drift downwards. But when they go into REM (Rapid Eye Movement) sleep (in humans thought to be associated with dreaming, so this is likely to be what’s happening to the seals too) they turn upside down and start to spiral towards the bottom of the ocean – one seal drifted down to 377 metres below the surface before waking up and heading towards the surface. Elephant seals can remain underwater for up to two hours without needing to take a breath, so this is probably quite relaxing for them. I wonder if they have that ‘where the hell am I’ feeling that I’ve been having when I wake up as I recover from jet lag?
In waters that are ‘only’ 250 metres deep, the seals will often take a nap on the ocean floor. This is something that other seals, including the endangered Monk seal, are known to do, and there’s a short video of sleeping seals here for your delectation.
And finally, and completely gratuitously, here are some Northern Elephant Seal pups. Instead of the impressive hooters of the adult males they have little snub noses. They are utterly trusting and relatively vulnerable, though I suspect they could still give you a nasty bite. Better to just admire them from afar, and be awestruck at how extraordinary this planet is.
I had no idea that some seals sleep under water.