This journal is brought to you by…
- Ms. Nadia Alm’s 4th grade class at Evangelical Christian School
- Ms. Clement’s 4th grade class at Bartlett Elementary
- Ms. Sarah Dormis’s and Ms. Jennifer Thompson’s 4th grade class at Westminster Academy
Say “Ahhhhh!”
Let’s take a look at the pearly whites inside the mouth of a Weddell seal!
Wow! Those look like some powerful teeth! I’m glad to not be a fish in the Ross Sea!
Take a look at the canines – the long, sharp, pointed teeth. You can definitely tell that seals are carnivores by looking at those canines! Carnivores are animals that eat meat (mostly fish, in this case), and their canines help them to do that. Those long sharp teeth are used to quickly grab prey and firmly hold it.
Weddell seals have 4 canine teeth – two on top and two on bottom.
Between the canines are their incisors – 4 on top and 4 on bottom. Do you see how much larger the outer two incisors are, compared to the 2 in the middle (both on top and bottom)? Weddell seals have a special use for these teeth.
Both the canines and the incisors stick out quite a bit! Do you know why that is?
Weddell seals live further south than any other seal. The Weddell seals that we are studying spend a lot of time swimming and diving under the sea ice in the Ross Sea. But how do they get above the ice to breathe?
With the help of their teeth! Their canines and incisors are specially adapted to help – they stick out! This adaptation allows them to ream, or break through, thin places in the ice to keep their breathing hole open. They must have really strong teeth to break through ice!
Check out this video to see how they do it!
VIDEO: https://youtu.be/u0HyM-ua1cM
Did you notice how far the seal opened its mouth to ream the ice? Just like our jaw, the top part is stationary while the lower part, or mandible, moves up and down. The Weddell seal can open its jaw very wide, which makes it easy to ream an ice hole or open wide to catch a foot-long fish!
With all that reaming, it’s no wonder their teeth show some wear and tear as they get older!
Back teeth – post canines
In the back of our mouths we have premolars and molars. We use them to grind food after we’ve taken a bite. But, check out the Weddell seal’s back teeth. They have what are called post-canine teeth. If you have a mirror, take a look at your molars and compare them to the picture of the Weddell’s post-canine teeth. How do they compare?
Our molars have a broad, rectangular shape and are basically flat on top with a slight dip in the center. They are specially adapted to grind food.
The post-canine teeth of a Weddell have a small, oval base which peaks to a rounded point. Do you think these teeth are used for grinding food, or do they have another purpose?
If you said no, you are correct! Since Weddell seals typically swallow their food whole (or nearly whole!), they don’t use post-canines for grinding food. Their teeth are used to help get the food down. Do you swallow your food whole like the Weddell seal? I hope not! We chew our food properly before swallowing. That’s why your molars are designed to grind food.
Weddell seal teeth vs. Leopard seal teeth
We’ve talked a little bit about predators. What are the predators of the Weddell seal? The main predators of the Weddell seal are killer whales and leopard seals. It is true that a leopard seal would love to eat a tasty Weddell seal pup for lunch, but it rarely gets the chance. Do you know why? Check out the picture below for a clue.
Notice the worn-down teeth on the skull of the Weddell seal (right). Now, look at the teeth of the Leopard seal (left). Do they look like they’ve ever reamed ice? No way – they are still sharp! They also point downward instead of pointing out like a Weddell seal’s teeth. Leopard seals can’t ream ice. This means they can’t live as far away from open water as a Weddell seal can!
What’s on the menu?
Weddell seals munch on Antarctic cod, silverfish, icefish, octopuses and squid. One of the things the researchers are interested in is the diet of the Weddell seal. For example, which do seals like to eat more, Antarctic cod or silverfish? Both fish live at similar depths of the ocean, but they have one big difference – their size!
Antarctic cod can weigh up to 150 pounds! That’s one big fish! Weddell seals eat most of their food underwater and swallow them whole, but it’s difficult to eat something as big as an Antarctic cod fish underwater! So, they have to bring it to the surface and tear it apart with those big incisors and canines! But, when they capture the smaller silverfish, they can swallow them whole underwater, and eat many fish during a single dive!
Why is this important to our study?
Weddell seals dive in bouts, meaning they dive over and over again and then will stop for a while, either to rest or because they aren’t hungry anymore. Our research team is interested in the length of each dive during a bout, especially the last dive of the bout. This can tell us a lot about what a seal is eating. If the last dive is much shorter than the other dives in the bout, then the seal probably grabbed a nice, tasty Antarctic cod to enjoy at the surface! If the length of time is the same, the seal probably filled up by eating silverfish underwater.
Check out the graphs below. They are both records of a Weddell seal’s diving, but the second graph has been color-coded by ‘bouts.’
By tracking this information, we may be able to get an idea of just how often a Weddell seal will munch on an Antarctic cod. This is very important, as there may be fewer Antarctic cod in this area than there used to be. How could Weddell seals be affected by declining numbers of Antarctic cod? What could possibly happen if the Antarctic cod disappeared completely?
If you have any hypotheses, send them to ‘Ask the Team!’
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