Category Archives: 2015 (01/03) All About That Fat; ’bout That Fat (yes blubber!)
…Ok, bad pun reference to Meghan Trainor’s song, but I need ways to amuse myself here on the Ice, right? We had a seemingly neverending series of storms from late December through January that made it hard for me to connect to the internet, but now that things have calmed down a bit I can get back to writing about life in the field. And today I’m talking about weddell seal pups, how amazingly fast they grow, and the purpose of blubber in polar animals.
In the end of November I hiked out onto the sea ice towards the pressure ridges that I explored last year, and on my way I passed a baby weddell seal pup with its mother on the ice. I’ll admit I’m a total sucker for baby animals, particularly chance sightings of wildlife in their natural habitat, but I still stayed a fair distance away from the seals so that I wouldn’t disturb the pair or make the mother feel too defensive for her pup. Luckily I had a zoom lens on my camera that let me take a few decent photos from farther away on the ice, and I’m pretty pleased with a few of the shots I was able to take.
The weddell pup was very cute but I was surprised by how *large* it was- at only two weeks old, this seal was already around 80 pounds. I spoke to a few of the seal biologists at McMurdo station after my sea ice hike and learned that this pup was 4ft long and weighed ~58 pounds when it was born, and continued to gain 4 pounds per DAY for the first six weeks of its life. In order to help the seals grow quickly, the milk produced by weddell mothers is so extremely fatty (60% pure fat) that it has the consistency of melted wax. This helps the pups gain enough blubber to keep warm in the Antarctic cold, and after six or so weeks, when the pups have quadrupled in weight (now approximately 240 pounds), they begin hunting and eating small fish and krill.
They continue to grow until they reach an average of 1200 pounds and are 11ft long, and as active adults they eat an average of 110 pounds of food per DAY. It’s hard for me to imagine that massive amount of food; a seal eating a pile of krill approximately the weight of my entire body on a daily basis. Even when compared to their total body mass, that appetite would be proportional to if I ate 11.4 pounds of food per day (compared to the 3-4 pounds of food eaten/day by the average healthy American adult). Needless to say, these seals are enormous. Even when I’ve been closer to them when adult weddells have approached near me in the past, I wouldn’t have imagined they were 1200 pounds just because they don’t stand up or tower over us in any way, so somehow I think it’s harder to envision their true size when they’re laying down. They remind me a bit of water balloons, sort of ‘spreading out’ their body mass when they lie on the ice, but that blubber is actually very dense and contributes 40% (nearly 500 pounds) of their weight.
In order to find out all of those facts I did a bit of research online, and while reading I learned a bit more about the purpose of having blubber- sure, it’s to keep warm, and it provides a source of energy when food is more scarce, but what’s the advantage of having more fat instead of having fur to keep warm? The answer, I learned, has to do with pressure. Sea otters have the thickest fur of any animal (one million strands of hair per square inch of skin!) which traps air in the fur layer and helps insulate the otters from cold water. Otters sometimes ‘roll’ in the water to introduce more air into their fur and help keep them warm.
Weddell seals, on the other hand, do not have a lot of fur. When weddells hunt, they can dive up to 2000ft below the surface in order to find food, but the deeper they dive, the greater the pressure of seawater pushing against their bodies. Thick fur wouldn’t help seals in that situation because fur is compressible– the large water pressure in deeper water would squeeze all ‘warming’ air out of fur. Blubber, on the other hand, is not very compressible, so it can provide a layer of insulation for seals even deep below the ocean surface.
Early explorers to Antarctica like Robert Scott and Ernest Shackleton used the high fat content of seal blubber for fuel and food, and during a visit to Cape Evans this season I actually saw (and unfortunately, smelled!) the enormous 104-year old blubber pile stored by Captain Scott’s team in 1911, but that’s a blog article for another day.