Sunday, November 9, 2014

Drop the (Antarctic Research) Bass

Exterior shot: Antarctic research station over the Ross Ice shelf. Except for a single lamp right outside the door it's the complete inky blackness of the southern winter. Motes of snow billow past through the light and we hear only the sound of rushing wind. The camera slowly zooms in on the entrance. Cut to Interior: Two researchers, a man and a woman, are settling onto cots. There's a dull orange glow from the lamp outside over everything. The woman looks over to the man.

Woman: I can't believe how quiet it is here. Back in Seattle I got so used to hearing the noise from the street that I'd forgotten what it's like in the field.

Man: Yeah everybody reacts a little differently. Some people love the isolation, others start to go a little nuts, start to think they're hearing things. Either way all you'll be hearing for next couple months is wind and creaking ice, so get used to it quick. 

Woman: I'll be fine, I've had enough of civilization lately. I'm ready for the silence.

Man: Good. I wouldn't want you going cracked on me with just the two of us down here. Let's get some rest.

They both settle into their cots and rest their heads on their pillows. The camera pans across the room and settles on the woman's face. She looks slightly unsettled, but calm as she slowly closes her eyes. The camera lingers on her face and all sound from outside dissapears, suddenly we hear this:  

And our heroine's eyes snap open! End Scene.

While that may sound like the first scene from yet another reboot of The Thing it's a situation that can actually happen in Antarctica. As ruined by the image on the clip; that sound is not an alien horror, nor the intro to the latest club sensation, but a cuddly seal. (Disclaimer: No wild animal should ever be cuddled, seals have no way of knowing that your hug isn't a grip of death and they will defend themselves, also they usually smell like fish and pee.) Specifically that sound comes from the Weddell seal (Leptonychotes weddellii) which breeds farther south than any other mammal. And they'd have the record for all animals too if it weren't for those meddling penguins. They were first reported on the ice above the Weddell Sea but they have what's called a circumpolar distribution. Basically that means they're found all the way around Antarctica on coasts and ice shelves.

Weddells live much closer to shore than the other Antarctic seals. Although they generally prefer shallower water Weddell seals have been found diving 600 meters down in search of prey! To give you an idea of how far that is, the deepest dive ever done on SCUBA equipment was only half as deep (332m Ahmed Gabr). While it may not be noticeable to us there is a big difference in ice real estate for Weddell seals.

Perfect example; no one wants a bedroom right next to the road
Courtesy Sandwich via Flickr

 Breeding age females and males hang out on ice closer to land than juveniles. The ice closer to shore is called fast ice because it's locked fast and doesn't shift around much. On the ocean side is the more familiar pack ice which gets packed onto and removed from the sheet pretty regularly. As you can imagine a constantly shifting environment isn't great for rearing babies. There's some contention among scientists as to whether or not the adults migrate from the fast to the pack ice, but it looks like most Weddells are pretty site specific.

One of the lines of evidence for this is the presence of the sounds you heard earlier. The trilling noise is unique to male Weddell seals. That sound is thought to be a territorial display since males use it all year round, but ramp up how often during the breeding season. Of course it's always possible that these seals just really love Doctor Who. Either way we know that, during the breeding season, males guard cracks and holes in the ice that females use to access the water.

How you doin'?
Courtesy Sandwich via Flickr

Of course those holes in the ice are also very important for breathing. Even though they can go without fresh air for up to 80 minutes at a time, being mammals means they still need to breathe between dives. In fact both male and female seals put quite a bit of effort into keeping the holes open. Fast ice has fewer gaps than pack ice, so the ones that are free need to be maintained. Weddell seals use their teeth to literally carve out thinner sections of the ice.

It's easy to assume the seals would keep breathing holes to themselves but they've been seen sharing these spaces. So scientists think that some of the underwater vocalizations are seals communicating about the breathing holes. Decoding the Weddell seals' language requires a lot further study; but it could be that seals approaching the surface are letting those already on the ice know they're coming, or seals at the holes telling those underwater where they can be found.

Weddells are the most well studied of all of Antarctica's seals, but we still know so little about them. Why do they have up to 30 different vocalizations? What are they trying to say? Do they get more inspiration from Depeche Mode or Daft Punk? Thankfully, Weddell seals have been relatively unaffected by the loss of ice in Antarctica so far, so there's lots of opportunity to learn the answers to these questions.


Weddell Seal (Leptonychotes weddellii), Wildscreen Arkive

Leptonychotes weddellii: Weddell Seal, Encyclopedia of Life

Doiron et al. "Proportional underwater call type usage by Weddell seals (Leptonychotes weddellii) in breeding and nonbreeding situations." Canadian Journal of Zoology, 2012, 90(2): 237-247, 10.1139/z11-131

Lake et al. "Spatial utilisation of fast-ice by Weddell Seals (Leptonychotes weddellii) during winter.", Ecography, Vol. 28 Issue 3 pg 295-306,  June 2005, DOI 10.1111/j.0906-7590.2005.03949.x 

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