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Here I am with three more of your flags in front of the McMurdo station sign. Photo credit: Alex Eilers
- Ms. Sarah Dormis’s and Ms. Jennifer Thompson’s 5th grade class at Westminster Academy
- Daughters of the American Revolution, Commodore Perry Chapter
- Ms. Samuelson’s 4th grade class at Oak Elementary
This seal is sporting a new fur coat! But is there a ‘cost’ to that coat? Photo Credit: Alex Eilers, MMPA Permit # 17411
If you are a Weddell seal, then you know the latest fashion trend in Antarctica is to have a gorgeous new coat of fur. And the adult Weddell seals typically start to get the new coat of fur each year in January or February! Seals are mammals. As mammals, Weddell seals have fur all over their bodies. And what fur they have! Look at this Weddell’s gorgeous coat! Weddell seals usually have silver-gray fur, often dotted with lighter spots. Seal hair is different from our hair. The fur is short, only about 1 inch long. It’s straight and more dense (meaning a seal has more hair per square inch) than the hair on our heads. When Weddell seals are first born, they have a fluffy, light gray coat with lots of warm, hairs. Let’s look at some more seals!
A young Weddell pup with lanugo fur. Compare it to the adult seals fur at the back of the photo. Photo credit: Amy Kirkham, MMPA Permit # 17411
Adult Weddell seals don’t have lanugo fur, because they don’t need it. They have a thick layer of blubber to keep them warm. But take a look at this seal pup. Does this fur look different?
Yes, that’s because it is different! Seal pups do not have a lot of blubber to keep them warm, so they need their fur to do that job. Pups have a fluffy, light gray coat with lots of warm fur called lanugo. This fur coat traps a lot of air that helps the pup stay warm… as long as the fur is dry! If the lanugo coat gets wet, then it isn’t a very good insulator (it’s like wearing a wet t-shirt!). So, as the pup gets older and bigger, and acquires its blubber layer for insulation, their soft lanugo coat is replaced by a more adult-like fur coat.
Weddell seal with an old brown coat. Photo credit: Alex Eilers, MMPA Permit # 17411
This seal’s fur is not very shiny or gray. This fur looks brown, dry, and brittle. Are some Weddell seals just prettier than others? No! So, what’s going on?
Molting is essential
Each year, Weddell seals molt or shed their fur. After an entire year of wearing the same coat of fur (in ocean water, cold temperatures, and high winds), their fur gets brown and dry. So, in late summer (late December through March), it is time to replace the old fur with a nice, new silver coat. This isn’t unusual; all mammals have to replace their fur/hair. Even humans! We are constantly growing and losing hair. Although, unlike seals, we grow new hairs all through the year. The Weddell seal only grows new fur once a year. Sometimes, we will find a seal that is halfway through the molting process!
Can you see the old and new fur? Photo credit: Dr. Jennifer Burns’ lab, MMPA Permit # 17411
It’s easy to spot the old fur in this photo. Photo credit: Alex Eilers, MMPA Permit # 17411
Fur, ice and sun
Weddell seals are often seen ‘hauled out’ or resting on the ice every year between October and February. This is spring and summer in Antarctica. The seals are taking advantage of the ‘warm’ sun. While it doesn’t feel all that warm to me, to a Weddell seal, it’s a little like sunbathing! Instead of a tan, the seals get a new fur coat! And the warmth of the sun probably helps the molting process. Scientists think that their new hair grows faster if their skin is warm.
Before we begin examining a seal, we take a thermal image of it. This is amazing! Thermal imaging is basically a photograph that shows the temperature differences of the seal's body. Check out this thermal image of one of the seals spotted last year. Notice the ‘red’ stripe down its dorsal side. The red color indicates that the dorsal area of the seal is warmer than the seal’s side. This dorsal area is also where the new fur is visible. It might be that the area on the seal where active molting is occurring is warmer than other parts. More research is needed to confirm this hypothesis but as Dr. Burns says, it is interesting to use technology to tackle tough questions in our research.
Compare the regular photo of the seal (left) to the thermal image of a seal (right). Photo credit: Dr. Linnea Pearson, MMPA Permit # 17411
An expensive new coat
Growing an entirely new fur coat is expensive! No, these seals aren’t spending money to get this new coat. They are spending energy! A seal’s fur is made of protein, like our hair, and making protein uses energy. Seals also need to keep their skin warm during the molt. This task uses energy too.. Do you see a problem with participating in two energy draining tasks at once?
If the seal is using energy to keep its skin warm, more of the seals body heat is lost to the environment. The seal then needs to burn more calories to maintain the same core body temperature. Seals also use up stored energy (body fat) just to keep their bodies running while they’re molting, since they don’t spend as much time the water looking for food.
One energy-expensive task for these seals is giving birth and nursing their pups. Raising a pup is so expensive that over the course of the nursing period (about 6 weeks), the new mom loses about 30 – 40% of her body weight! Wow, that’s a lot!
It is not likely that a female seal will do these ‘expensive’ tasks at the same time. First comes nursing, then molting. This is smart! You don’t want to spend all of your energy at once! Most seals that have a pup don’t start molting until at least a month after weaning their pups. This way, they have a break after nursing, which they use to find lots of food and gain weight. The weight they gain can then be the fuel that powers them through molting.
This Weddell seal is starting to molt. Can you tell what stage it is in? Photo credit: Alex Eilers, MMPA Permit # 17411
Fur sample science
The molting process is one of our main focuses this year out on the ice. Weddell seals have a very specific time frame for their critical life history events, like pupping and molting. Our research team wants to better understand these ‘big events,’ and how environmental factors may affect these changes.
So, how do we do this?
First, we observe which seals are molting and how far along in the molt they are. Weddell seals molt their fur in a pattern. First, they shed the fur on the tops of their heads and their backs. Next, they shed a bigger stripe on their backs. The stripe gets wider and wider until the seal has new, silver fur all over. Based on how much fur is molted, we can put the seal in a molt category. Then, we can see how many seals were in category 0,1,2,3 or 4 at different times. We can also note if the seal’s molt category is related to whether they had a pup or how fat they are.
Weddell seal molting categories. Photo credit: Amy Kirkham
Every time we capture a seal, we also take a small fur sample and a skin sample. We study these samples in the lab. These little bits of fur and skincan actually tell us a lot – what stage of growth their fur is in, whether it is new fur or old fur, and lots of other stuff. To get the samples, we shave a little patch of hair.
This shaved patch serves another purpose. We’ll be trying to find these seals again in January. The first thing the research team will do is see if the hair in that shaved patch has grown back! In the past, we’ve seen that the ‘skip breeders’ (the seals that had not had a pup), had completely regrown their hair. The new moms, on the other hand, had little to no growth in the shaved patches.
Why aren’t the new moms re-growing their fur? It looks like the ‘skip breeders’ are molting earlier than breeding moms. Why is this happening? Our research team is trying to figure that out, but they do have a hypothesis!
Remember how expensive raising a pup is? The ‘skip breeders’ that did not recently have a pup didn’t have to spend all that energy, so they have more energy stored up. This store means they have the fuel they need for the molt ready early in the summer. It is in the seals’ favor to molt sooner, so that they don’t have to molt at the end of summer when it starts to get really cold. At least that’s what the scientists hypothesize. The sooner they molt, the sooner seals can get back to foraging more and start rebuilding their energy stores again!
How do they build energy stores?
They eat, eat, eat!
This is our hypothesis, and right now, we are learning whether fatter seals are growing fur before skinnier seals. With the samples and measurements we take, we can figure out if food and energy are, indeed, what control when a seal molts.
Who knew you could learn so much from a little sample of fur?
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