Siren Songs

Last week we looked at one of the most productive ecosystems on earth, sea grass prairies. Sea grass prairies house many animals that fill very similar ecological roles to terrestrial counterparts. The most notable, and tragically least discussed in the previous post, is the manatee. Thankfully manatees and their cousins are such a rich topic that they've earned their own post.

 Try not to look so excited, geez.

Courtesy Tracy Colson via Flickr

Almost everyone has heard that manatees are likely the source of mermaid legends, or at least were mistaken for mermaids after the legend had been around for a while. In fact the name of the manatee's order, Sirenia (pronounced: sih-ree-nee-uh), actually comes from the sirens that tempted Odysseus while he sailed from home after the Trojan War. Many people find it a bit surprising that such large, grey, and cowish looking animals could be mistaken for half women, half fish; but beyond sailor's missing home there's actually a decent reason sirens could have been mistaken for their namesake. Female sirenians have breasts in the exact same position that human females do. Add the fact that they nurse their young while floating vertically with their heads above water, and you can see how people could have made the mistake that there were aquatic humans.

Though manatees are often called sea cows; it's believed that sometime around 50 million years ago a close relative of elephants slipped into lakes and streams to feed on the rich grasses growing underwater. Over time these four-limbed sirens became more and more adapted to the life aquatic and their descendants spread out across the globe. Then as the earth cooled to today's more familiar state many sirenians went extinct, leaving us with only four species.

Unfortunately there isn't anywhere in the world where you can see all 

four species at once. This manatee quartet (dibs on the band name) is made 

up entirely of one species.

Courtesy: David Hinkel via Flickr 

All sirenians scour the river, lake, or sea floor searching for underwater grasses to eat. Other marine mammals eat meat, and so have access to copious amounts of fat and protein to keep their weights up and their bodies warm. Sirenians are the only herbivorous marine mammals so they have to eat about 10% of their weight every day. Quite a lot when you consider they can weigh between 500 and 800 lbs. One study found that a single sirenian needed about an acre of constantly regenerating sea grass per year in order to get the food they need.

Sirenian mouths are well adapted to consuming large quantities of plants.  On every species the mouth is turned downwards to the seabed so the siren can look ahead as it grazes. Their teeth are specialized for grinding up veggies and are constantly replaced with new ones as they wear down, just like a shark's!

Modern sirenians are all found in the fresh and nearshore salt waters of the tropics and sub-tropics. They're extremely intolerant of cold and will move out of waters that fall below about 68 degrees Fahrenheit (20C). This need for environmental warmth may be a consequence of having evolved during a much warmer period in Earth's history. Only one sirenian, the Steller's Sea Cow (Hydrodamalis gigas), managed to adapt to frigid waters and survive to the modern era, but believe it or not, we ate them all. 

In case you ever thought your drawing skills aren't good enough for natural history; 

this is thought to be the most accurate drawing of a Steller's sea cow because 

it's the only one we know was drawn from a live specimen

Courtesy: Public Domain via Wikimedia Commons

Steller's sea cows were discovered by westerners looking to hunt sea otters along the Aleutian Islands where food could be scarce. The scientist who first described them tells us that they ate more algae than sea grass, and that their forelimbs were curved instead of paddle shaped to allow them to pull themselves along in the shallows while grazing. What's particularly fascinating about these animals was just how big they were, some individuals were as long as an adult orca! That's a lot of manatee. Steller's sea cows were so slow, easily reached, and edible that they were gone about 17 years after their discovery. Sadly we'll never know if we did major detriment to this species while it was thriving in an isolated population, or if they were already nearing extinction naturally when we dealt the final blow. Fortunately there may still be time to save the sea cow's closest relative, the dugong (Dugong dugon).

Om Nom Nom Nom
Courtesy: Corrie Barklimore via Flickr

Dugongs (no, not the pokemon) are the most marine of the sirenia; meaning they spend all their time in salt or brackish (mixed salt and fresh) water. Their most noticeable distinction from manatees is their forked dolphin-like tail. Manatees have big, round, paddle-like tails that are useful for holding position in still water. While dugongs are wide spread across the tropical Indian and Western Pacific Ocean their populations are spotty, probably due to human alterations in their habitat. The largest herds live along the coast of Northern Australia and in the Arabian Gulf where sea grass beds are still large and healthy. The challenge for these sirens has been human development of beaches where sea grasses grow off shore. Unfortunately sea grasses grow off of exactly the kind of sandy, relaxing beaches humans like to put hotels and beach communities on. When land plants are taken away by construction; dirt and sand run into the nearshore smothering the prairies. Fertilizer runoff from agriculture and golf courses also causes quick-growing algae to out compete sea grass. So when you choose a place to stay during your tropical vacation, keep in mind the resort's potential impact on dugongs before you book a room.

Dugongs role as grazers is extremely important for sea grass prairies because they remove old grasses and fertilize new ones. As they browse, dugongs pull sea grass up by the roots creating noticeable  tracks of bare sand like someone set the lawnmower way too low. Like any herbivore dugongs make a lot of waste and as their poop falls into the furrows they've created in the grass it provides critical nutrients for the regeneration of the prairie.

Who else wishes it was possible to hire manatees to mow
your lawn instead of goats?
Courtesy: Ruth Hartnup via Flickr

The sirenian that is the next most comfortable in ocean is the West Indian Manatee (Trichechus manatus). West Indian Manatees are the most familiar and well-studied of all sirenians because they live in highly populated regions of North, Central, and South America. You may have heard of Florida and Antillean manatees in your travels, and those are legitimate, but they are names for distinct populations of West Indian Manatees. Antillean manatees are usually found in the Southern Caribbean, and Central and South America. You can probably guess where Florida manatees are most often found. For a deeper look at what makes a species, and how populations of one species can be distinct from one another without being totally different, check out the D&T posts "Celebrating Sculpin Speciation" and "Ghost Faced Killer (Whales)".

Most West Indian manatees split their time between fresh and salt water depending on the season. In Florida these manatees spend their winters huddled nears springs of warm water, and since the advent of modern electricity generation, the heated water outflows from power plants. As ocean temps warm up in the summer Florida manatees  spread out in search of lush prairies and can be found travelling as far north as Virginia! Interestingly, although as many as 500 manatees have been seen in one spot during the winter, they aren't particularly social. The mother-offspring bond is the strongest social connection in manatees. Young manatees will stay with their mothers for two years after they're born, learning where warm refuges and feeding grounds are located.

The green on his back is algae, kind of like the stuff that grows in sloth fur.
Courtesy: Keith Ramos via Flickr

The final two sirenians are the most river-adapted species, the Amazonian manatee (Trichechus inunguis) and the West African manatee (Trichchus senegalensis). Both can be found deep into large rivers in their respective continents. Amazonian manatees have stable populations as far up the Amazon water shed as Peru and Columbia, and West African manatees can be found living in lakes 200 miles inland from the sea. These manatees deal with particularly murky water compared to dugongs and West Indian manatees, so the sensitive bristles that cover all sirenians' bodies are especially important for finding food. It's kind of like if a cat had whiskers all over their body instead of just their face.

Yep, that's a baby Amazonian manatee. Commence squealing with delight
Courtesy: Harvey Barrison via Flickr

We know the least about African manatees because the humans of their homeland have struggled with colonialism and the unrest it often instills in the colonized. However, this chaos may actually benefit the manatees; as development in some countries where they're found has been slow. Without speed boats, big riverside properties, and erosion problems African manatees have fewer risks to their survival than sirens in more altered regions of the world.

Dugongs and manatees are one of the weirdest and most fascinating marine mammals on the planet. For every human that's encountered them it's as hard to resist the song of these sirens calling us to discover more about them. But unlike the sirens of Greek Myth, the lure of dugongs and manatees will bring every species to a healthier life and a richer planet.

References:

Mayaba, Theodore B., Kamla, Aristide T. & Self-Sullivan, Carlyn, "Using Pooled Local Expert Opinions (PLEO) to Discern Patterns in Sightings of Live and Dead Manatees (Trichechus senegalensis, Link 1785) in Lower Sanaga Basin, Cameroon", PLOS ONE, July 21st, 2015.   

Satizabal et Al., "Phylogeography and Sex-Biased Dispersal Across Riverine Manatee Populations (Trichechus inguinus and Trichechus manatus) in South America", PLOS ONE, December 20th, 2012.

Accessed via: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0052468

Sulzner et Al., "Health Assessment and Seroepidemiologic Survey of Potential Pathogens in Wild Antillean Manatees (Trichechus manatus manatus)", PLOS ONE, September 12th, 2012.

Accessed via: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0044517 

Macdonald, Nicole, "Dugong dugon- Dugong" Animal Diversity Web. Accessed via: http://animaldiversity.org/accounts/Dugong_dugon/#food_habits

Weinstein, Brett & Patton, James, "Hydrodamalis gigas- Steller's Sea Cow", Animal Diversity Web, Accessed via: http://animaldiversity.org/accounts/Hydrodamalis_gigas/

Ghost Face Killer (Whales)

December's post got the Depth and Taxa crew thinking. We talk an awful lot about fish and invertebrates on this blog. Of our 32 posts only three directly refer to marine mammals. While it's great that we're bringing the less publicly well-loved species into the spotlight; it's sad because the ocean's mammals are astonishing. Whales, dolphins, porpoises, seals, sea lions, walruses, and sirens (the manatee kind, not the Odyssean) all exhibit remarkable adaptations for a class of animals that arguably don't belong underwater. So in the interest of fairness and the spirit of deeper understanding, let's talk about the biggest, the baddest, the black and white-enest of the dolphins; Orcinus orca, the Killer Whale.

They're like the pandas of the sea! If pandas ate exclusively flesh...

and hunted in groups... and had complex social structures... 

They're like the wolves of the sea!

Courtesy: Matthew Allen via Flickr

Okay so the first thing you might be wondering is how we can call them killer whales if they're dolphins? Well the word "whale" is deceptively complicated. See, back when the common conscious was still in its "everything that swims is a fish phase" a whale was just anything really large that you saw or caught in the ocean. More recently whale has mostly been used to mean any large species of cetacean (pronounced: set-ay-shun). If you've ever called something a whale, porpoise, or dolphin; it's a cetacean. Dolphins are a specific family within the cetaceans, so orcas are both whales and dolphins. 

Just like humans, orcas can be found all over the globe; from the tropics to the poles. They live in groups comprised of their relatives and close associates, just like us. They're the apex predator in their environment, just like us... They live 50-60 years but can get over 100... just...like...us... Hm these similarities are starting to get a bit strange.

Okay, this is officially weird now. 

Courtsey: Douglas Muth via Flickr

 

The truth of the matter is, humans and orcas are both extremely successful because of our large, wrinkly brains and penchant for caring about others of our own species. In humans the prime example of this one-two punch of emotional intellectualism is just how much listening to "Hello"  makes us want Adele to find happiness <sniffles>. In orcas it's their ability to form what are called ecotypes.

There are at least ten orca ecotypes between the northern and southern hemisphere, and likely more to be discovered. Each has its own feeding strategy, typical body type, and associated behavior. Usually more than one ecotype is found living in the same place. Take for example the continental shelf of the northeast Pacific. These nutrient rich waters are home to the kind of expansive seafood buffet usually reserved for Red Lobster and questionable casinos. Fish, birds, mammals, and invertebrates are all in ready supply if you're clever enough to harvest them. This smorgasbord has allowed for three different ecotypes to develop in one region.

Courtesy: Dahlheim et Al. (2008), Marine Mammal Science, 24(3)

The most well understood of these three types are the resident killer whales. There are three populations of resident orcas in the northeast pacific; the Alaskan Residents, the Northern Residents, and the Southern Residents. All of these groups live in fairly large pods of usually around 30 individuals. Occasionally the entire Southern Resident Community gets together for a big ol' fashion hootenanny. Seriously, this 85 whale strong "superpod" is as close to a college kegger as any species other than humans get. This is the time when the Southern Residents say hey to friends, hook up with each other, and shout across the room to orcas they know. That last one is only partly a joke. Resident orcas are the chatty Kathy's of the ecotypes. They're highly vocal because their favored prey requires them to be highly coordinated in their hunting.

Resident orcas eat nothing but fish, and about 90% of that fishy diet is salmon. Why? Because salmon meat is just drowning in oil. Those natural fats are great for preserving the whales' blubber layer, which keeps them warm. Salmon is also absolutely dense with chemical energy, and that's essential for maintaining an active body and mind. 

All orca ecotypes employ echolocation clicks to navigate their environment. But in order to effectively corral schools of speedy fish, residents employ a complex vocabulary of whistles. Their calls regularly change pitch, tone, and frequency as they communicate with one another. 

"So anyway I said to him" 'go left', and he went right, so I said: 'no, 

your left', and he said: 'What do you mean I'm left? we're all still here'" 

Courtesy: Tundra Ice via Flickr  

Resident oracs are usually the ecotype that people are most familiar with. This is mostly due to the fact the they remain in a relatively small area throughout their lives. The Southern Residents are probably the most extensively studied and photographed whales in the world. They have legions of fans, and what's not to love about residents. They're rarely far away when you need them, they're gregarious, and they eat food that we don't find particularly cuddly. Transient orcas, also called Bigg's killer whales, are an entirely different story.

Transients are the leather jacket wearing, smoking behind the gym, switchblade carrying, greasers of the ecotypes. Everyone who's ever loved a bad boy or girl can get into the transient orcas. "What makes transients the badasses of the dolphins?" I'm glad you asked.

 Courtesy: Poorly Drawn Lines

Transient orcas are primarily mammal eaters, and they almost never touch fish. This ecotype preys upon seals, dolphins, porpoises, occasional birds, and even baleen whales! With each prey type comes a different hunting strategy. Seals are usually grabbed from below the surface and quickly killed, but in contrast, sea lions are gradually beaten to death with the tails of each pod member. Then this frequently happens:

Hahaha Okay I admit this at least a little funny.

Yup, they play with their food. Take what your average cat does to a mouse, scale them both up about 1000 times, and you have a Biggs' killer whale playing with a sea lion. But wait! It gets even more intense. Transients hunt the giant cetaceans by drowning them. I'll let the BBC and David Attenborough give you the specifics in the video below

Really intense footage, but absolutely incredible.

Although each attack type has different characteristics, what's consistent is that transients are quiet and work with a small crew. They swim in loosely defined small pods, usually no more than 10 individuals, to increase each whale's share of the prey. And since their prey hears very well, transients go into stealth mode once they've identified a target. Only once they've taken down their meal do they resume vocalizing. 

While all of his mammal killing may seem unpleasant, it actually makes a lot of sense. Since resident orcas are busy eating up all the oily fish in the nearshore, transients need another source of fat. And there's few higher quality fats than the blubber of marine mammals. By consuming different foods transients and residents can live side-by-side with little interaction and no conflict.

So if Bigg's killer whales and residents consume all the energy rich prey in the nearshore then the third ecotype must live somewhere else. 

It's on the shore isn't it? I knew this would come back to pandas.

They're like the orcas of the land!

Courtesy: fortherock via Flickr

The final of the northeast Pacific ecotypes lives in the offshore environment along the edge of the continental shelf. In one of the most creative namings ever, these offshore orcas are called... offshore orcas. Offshore's are the least well understood of the three ecotypes for a number of reasons. The main being, that the open ocean is so much bigger than the inland waters where transients and residents are usually found. It's not surprising that most of the encounters with offshores have occurred off of California where the open ocean abuts the continent.

"California whales they're so incredible. Black tail flukes, 

with blowholes on top"

Courtesy: Matthew Allen via Flickr

Genetic studies have found that offshore orcas are probably most closely related to residents. They're also similar to residents in their behavior and  general diet. Offshores appear to be fish eaters and live in very large pods, sometimes more than 100 whales strong. It's not clear if this is similar to the summer superpod that the southern residents get into once a year, or something else entirely. 

Where residents and offshores differ is in how far they'll travel, and exactly what kind of fish they eat. The same group of offshore orcas have been seen at Dutch Harbor in the Aleutian Islands, and Dana Point in California. That's 4,435km if the pod swam in a straight line, which it almost certainly didn't. In contrast the Southern Resident population only leaves the Salish Sea near Washington and British Columbia on occasion.

Courtesy: Dahlheim et Al. (2008), Marine Mammal Science 24(3)

We don't have a great idea of offshore killer whales' diets, but they seem to be less picky than residents. They've been seen attacking schools of baitfish, and beating blue sharks with their tails. They've also been found beached with salmon and halibut in their stomachs. Another piece of evidence has led some scientists to speculate that sharks are a major component of their diet. 

When offshore orcas wash up on beaches their teeth are frequently worn down almost to the gumline. Even young animals, whose teeth can't have eroded from age, show a lot of wear. Sharks have rough, sand-papery skin that could probably buff an orcas teeth down to the jaw if they eat them all the time. Offshores also have fewer tooth marks on their bodies from scrapping with other orcas, suggesting their teeth aren't very pointy for most of their lives.  

We've barely begun to scratch the surface of offshores' life history even though we've known about them since the 80's. In fact there's so much more to learn about all three ecotypes. Their behaviors and life styles are so different that they might even warrant being considered several species of orca. But for now, killer whales are a single group of highly intelligent, adaptable, long-lived, nomadic hunters, just like humans before agriculture and urbanization. Killer whales, they're like the humans of the sea!

Several ton, fish-eating, flippered, black and white, humans.

Courtesy: Putneypics via Flickr

References:

Dahlheim, Shulman-Janiger, Black, Ternullio, Ellefrit, & Balcomb, (2008) "Eastern Temperate North Pacific Offshore Killer Whales (Orcinus orca): Occurence, Movements, and Insights into Feeding Ecology", Marine Mammal Science 24(3): 719-729, doi: 10.1111/j.1748-7692.2008.00206.x

Accessed via: http://www.orcanetwork.org/nathist/offshoresdalheim.pdf

Dahlheim & White, (2010) "Ecological Aspects of Transient Killer Whales (Orcinus orca) as Predatorsin Southeastern Alaska", Wildlife Biology 16:308-322, doi: 10.2981/09-075

Accessed via: http://www.orcanetwork.org/nathist/Dahlheim2010.pdf

Ford MJ, Hempelmann J, Hanson MB, Ayers KL, Baird RW, Emmons CK, et Al., (2015) "Estimation of a Killer Whale (Orcinus orca) Population's Diet Using Sequencing of DNA from Feces", PLoS ONE, 11(1): e0144956, doi:10.1371/journal.pone.0144956

Accessed via: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0144956

Riesch & Deecke, (2011), "Whistle Communication in Mammal-eating Killer Whales (Orcinus orca): Further Evidence for Acoustic Divergence Between Ecotypes". Behavioral Ecology sociobiology, 65: 1377-1387, doi: 10.1007/s00265-011-1148-8

"About Killer Whales", Center for Whale Research 

Accessed via: http://www.whaleresearch.com/#!about-orcas/c1qa8

 

A Sea Lion Story

By now it's probably come across your computer screen at least once. The story may have even shown up in your physical paper. More than 1,800 California sea lion (Zalophus californianus) pups have shown up emaciated on the beaches of California since January. Unusual mortality events like this are most troubling to us because it's adorable baby animals that are suffering, so it's a good opportunity to draw awareness to ecosystem scale issues.

D'aww who's a good vector for a better understanding

 of ecology!? You are, yes you are!

Courtesy: Jaina via Flickr

So what do baby sea lions have to do with the ecosystem as a whole? Well ecosystems are all the living and non-living things in an area that interact with one another. This means that every piece in an ecosystem is significant to the others in some way. For example small fish are important to large predators, currents are important to plankton, and temperature is important to everyone. Each piece has direct effects on the others and those effects themselves interact.

On the surface (pun intended) starving sea lion pups seems to have a pretty straightforward cause. You would assume it's because there isn't enough of whatever it is sea lions eat. That's part of the story, but there's more to it. When baby seals and sea lions are first born they lack the thick blubber of their parents. Pups have to drink extremely rich milk to bulk up enough to survive on their own. California sea lion milk averages about 35% fat, that's about the same fat content as whipping cream, and about ten times the fat content of whole milk. Not only does the thick layer of blubber the pups develop help keep them warm it's important as an energy reserve when they first strike out on their own.

Despite what this sea lion seems to be telling you, Cronuts are not 

a viable source of energy reserves.

Courtesy: Makitani via Flickr

The most important prey for lactating mothers are anchovy, sardine, and hake. These fish live in large schools, so they're usually plentiful and they have extremely oily flesh; perfect producing rich milk. In the past there were very large fisheries for these species off of California. Think Cannery Row on Monterey Bay. However, we aren't taking too much of the sea lions' food away anymore because canned, oily fish have declined in popularity.

I can't imagine why...
Courtesy: dr.coop via Flickr

 What's happened is that for the last few years the waters around the Channel Islands, where the sea lions give birth, have been abnormally warm. Each of the fish the sea lions rely on are cold water species, in fact North Pacific anchovy won't go into water warmer than 62 degrees F. Since California's seas have been so warm the food fish have shifted themselves to colder waters. Sardines have been spawning farther offshore and other fish schools have moved north. These migrations have forced mother sea lions to hunt farther afield, and when their moms don't come back for extended periods of time, the pups set out on their own too early.

So where are the dad's in all this? Why don't we see adult males stranding in California? Well they're not there. Male and female sea lions both take on long migrations from British Columbia to California and back every year, but they have different schedules. Females head down to the breeding grounds first to give birth. Then males head down to meet up with the females once they're ready to mate again; about three weeks later. Being further north for longer has actually lead to boom times for male sea lions. At the mouth of the Columbia river between Washington State and Oregon more than ten times the usual number of males have been hanging out. They came in for this year's copious smelt run and are fattening up to make the trip south to the rookeries. Males need a lot of mass and energy reserves to defend territories on beaches which they won't leave and thus don't eat for several weeks.

   "I'll calm when I haven't gone twelve days without food!"
Courtesy: Bridget Samuels via Flickr

So that's the story. Warm water pooling at the surface has pushed forage fish away from the Channel Islands. This means that female California sea lions have to travel farther to find food that makes rich enough milk for their babies. These longer trips mean that many young are leaving the rookeries too early, and are washing up along the shore. All the while, farther north, males are enjoying a greater supply of food than ever. The biological needs of its inhabitants, and the physical characteristics of the ocean come together to tell the complex story of an ecosystem as long as a continent. We're able to discover the changes happening in the environment thanks to this single species.

Scientists aren't sure if the warming is caused by the changes happening to the global climate system, or if this is part of natural variations of the Pacific. Either way marine mammal stranding networks will need support in the near future. If you want to help one of the best things you can do is to remain informed about who's best prepared to help hungry or sick sea lion pups. There's a good list of organizations to contact and a lot of information here.

References:

"California Sea Lion (Zalophus Californianus)", NOAA Fisheries: Office of Protected Resources. Accessed via: http://www.nmfs.noaa.gov/pr/species/mammals/pinnipeds/californiasealion.htm

Bernton, Hal, "Boom Times on the Columbia for California Sea Lions", The Seattle Times, March 27th, 2015, Accessed via: http://www.seattletimes.com/seattle-news/boom-times-on-the-columbia-for-california-sea-lions/

"2013-2015 California Sea Lion Unusual Mortality Event in California", National Marine Fisheries Service Health and Stranding Reports,
Accessed via: http://www.nmfs.noaa.gov/pr/health/mmume/californiasealions2013.htm

Redman, Marianne, "The Pinnipeds: Seals, Sea Lions, and Walruses", pg 282, University of California Press, 1990.

Orr et al., 2011, "Intraspecific Comparison of Diet of California Sea Lions (Zalophus californianus) Assessed Using Fecal and Stable Isotope Analyses", Canadian Journal of Zoology, 89:109-122. 

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.

References:

Weddell Seal (Leptonychotes weddellii), Wildscreen Arkive

http://www.arkive.org/weddell-seal/leptonychotes-weddellii/image-G53852.html

Leptonychotes weddellii: Weddell Seal, Encyclopedia of Life

http://eol.org/pages/328638/details

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