The “Inside” Scoop: Great White Shark

I hope everyone is having a great weekend! As promised, I have a non-avian focused post this week! It’s another “Inside” Scoop installment, this time about the magnificent and intriguing Great White Shark. As usual, I provide time stamps in case you want to skip around the documentary, and viewer discretion is advised. Enjoy!

White_shark

Great white shark by Terry Goss, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=1561215

The great white shark featured in this documentary was caught in beach protection nets in South Africa. It was a 900kg (~1,985lb), twelve-year-old, female shark.

4:04 – The veterinarians and anatomists begin the episode by pointing out a curiosity about the shark – that its stomach was in its mouth! Apparently, great white sharks can invert their stomach to expel difficult to digest food (e.g. bones) or because of extreme stress, which is the most likely explanation in this case since the animal was caught in a net.

5:08 – The dissection begins with a closer examination of the skin. Great white shark skin is rough, like sandpaper. Richard Dawkins explain at 6:20 that the skin is actually comprised of tiny micro-teeth. These micro-teeth are composed of the same material as the shark’s main teeth, which likely arose from the skin. (7:35) A shark’s primary teeth are only loosely held in the mouth because they are basically on a tissue conveyor belt. Shark teeth are rotated out of the mouth and replaced because the tissue that they are attached to grows outwards.

Shark, Tooth, Lower Jaw, Inside, Molt

Example of shark teeth in rows

 

8:57 – The crew goes out on a boat to try to obtain a bite force measurement on a great white shark. I thought this part of the documentary was really interesting because they compared a shark’s bite force to a crocodile’s. I thought that the shark’s force would be larger, but the fact that the shark’s teeth are not attached to its cranium gave it a major disadvantage in terms of bite force. (12:35) In a previous Inside Nature’s Giants episode, they measured a crocodile’s bite force to be ~1,413 lbs, but they have a measured maximum of ~3,000 lbs. This extreme force is likely because crocodiles have to hold on to their prey and drown them, whereas sharks try to steal chunks of their prey. At 13:00, they got a shark to chomp some chum at 90 lbs of pressure. This was relatively weak since maximum bite force for great whites can range up to 500-600 lbs. However, sharks usually do initial, exploratory bites before putting their full force behind an attack. This is the reason that many shark attack victims get away with their lives.

16:22 – The free-floating jaw of the great white does have some advantages. It allows the shark to project its jaw, thereby getting a bigger bite area. This time stamp gives you a neat animation of this feature.

17:54 – Getting into the gills! Anatomists show why sharks, just like Dory, have to “just keep swimming.” Sharks have to constantly move to have a continual oxygen exchange through their gills and gill filaments. The video shows an interesting animation at 19:22 of the evolution of the shark’s gill bars that hold up the gill filaments. It is likely that the gill bars developed a hinge and could then help pump water through the gills more efficiently. Consequently, the front gill bars were free to develop into a jaw for attacking prey.

20:33 – Shark cage time! One of the anatomists gets up close and personal with some great whites.

24:30 – Shark vision! They do not actually have eyelids. Shark eyes physically roll back into their head for protection. At 24:45, the scientists dissect a shark eye and show just how tough the outer layer of the eye is.

26:30 – Animation of water flow through a shark’s nose. Great whites have an inlet and an outlet for water in their nose. Their noses are designed to detect very small particles in the water and help them hone in on prey. However, great whites also have other highly developed sensory systems, such as the lateral line (27:27). The lateral line is a sensory system within/along the shark’s skin that detects vibrations in the water. In addition, sharks possess Ampullae of Lorenzini on their snouts (above and below, 28:05). These ampullae look like little pores on the outside of the head, but they are actually filled with a special type of liquid that allows sharks to detect electromagnetic signals from their prey. Because of the extensive sensory system in a shark’s head, a solid hit to their snout temporarily dazes them by overwhelming their sensory systems (ya know, just FYI, in the case of a shark attack. However, the documentary did highlight that more people die in fights with their kitchen toasters every year than shark attacks!)

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Electroreceptors in a shark head, including Ampullae of Lorenzini and lateral line receptors

29:20 – Male vs. Female. Anatomists show what claspers look like on a male shark and explain that claspers go inside the female to help hold on to them while releasing sperm.

31:00 – Sharks do not possess swim bladders, so how do they maintain their buoyancy? They have a MASSIVE, oil-producing liver! I have dissected many dogfish sharks in my day but seeing the sheer size of a great white shark liver was insane! It takes up almost the entire body cavity!

35:10 – Sharks are made up completely from cartilage. Although this helps them stay lighter, it also means there are not many fossils available to study. However, ancient shark teeth have provided some evidence of Megladon, or “big tooth,” a shark that would make current-day great white sharks look like babies.

37:07 – The necropsy continues with the digestive tract. Because the liver takes up such an overwhelming amount of space, the intestines are super compact. Sharks have a spiral valve in their intestine to increase surface area. It is basically a spiral staircase in digestive form. Really cool to see in the great white!

39:50 – Great whites are more “warm-blooded” than “cold-blooded” because they have to constantly remain in motion. Red muscle in the shark’s tail allows it to maintain a warm body temperature, but white muscle tissue lets the shark have quick-action power when necessary.

41:30 – Short clip of radio tagging great whites in South Africa.

43:25 – Quick look at the brain and the unbelievably large proportion of it that is taken up by sensory input.

46:02 – Preview of the incredibly real threat that sharks are facing from the finning industry. Over 70 million sharks are killed every year just for their fins alone. The documentary did not have adequate time to elaborate on the threat of finning, but feel free to check out a previous post that I wrote on shark finning: The Scoop on Shark Fin Soup. I hope you gained a new appreciation for our misunderstood, finned friends! Until next week!

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One response to “The “Inside” Scoop: Great White Shark

  1. Pingback: The “Inside” Scoop: Crocodile | bloggerheadseaturtle·

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