Great White Shark (Carcharodon carcharias)
By: Charlotte C. Schroeder
Undergraduate Marine Biology Student
Skeleton
Great white sharks (Carcharodon carcharias) have a cartilaginous skeleton, as they belong to the class Chondrichthyes, which represents the group of cartilaginous fish. Having a skeleton made of cartilage unlike other fishes proves to be incredibly beneficial for these apex predators. Bone is more dense than cartilage, so having a cartilaginous skeleton allows white sharks to be able to turn and maneuver more quickly throughout the water column without expending too much energy. Sharks also lack the swim bladder, which most fish utilize to remain buoyant, so having a cartilage skeleton also helps white sharks with buoyancy, as cartilage is half as dense as bone is.
Great white sharks also lack ribs in their skeleton, allowing them to produce even sharper and faster turns; which is highly beneficial for hunting their agile, almost acrobatic pinniped prey. Overall having a cartilaginous skeleton in their physiology is highly beneficial for great white sharks as this type of skeleton not only helps them make sharp, twitch movements when hunting down prey but also helps them remain buoyant throughout the water column.
Image provided by: African Shark Eco Charters
For more information on pelagic shark thermoregulation, please visit Christopher Seng's website, Section 3: https://spark.adobe.com/page/tbV2sE1ydctAc/
Reproduction
Image Provided By: ABC News
Although there is still much unknown about great white shark reproduction, due to scientists only being able to dissect 10 female specimens so far, we do know some key knowledge about their reproductive behaviors. Great white sharks (Carcharodon carcharias) are ovoviviparous animals, meaning that they undergo internal fertilization, but not in the traditional way most animals preform. The overall getsation period for white sharks is between 12 and 18 months, as estimated by scientists so far. Due to this prolonged gestation period, female white sharks are able to rest by being able to give birth every two years. Great white sharks grow an egg inside of their uterus in which the embryo begins to develop and grow. Once hatched from their egg, the shark embryos then feed on the unfertilized eggs within the mothers uterus; this is called oophagy. So essentially, great white sharks embryos are already learning to hunt inside of the womb.
Image Provided By: The Charlotte Observer
The picture on the left shows a great white shark embryo, which is one of the only photos ever taken of a white shark juvenile prior to birth.
The picture on the left shows a ovoviviparous Dogfish embryo I dissected in my Ichthyology class, where the egg and yolk sac can be clearly seen connecting the umbilical cord to the embryo.
Image Provided By: Me, Charlotte Schroeder
During mating, great white sharks have been hypothesized to undergo a courtship ritual. This theory has been hypothesized by scientists due to the bite and scratch marks seen on many female sharks, where they assume males tend to bite the female in order to hold onto them. Once the male and female are held together, the male uses fin-like appendages called claspers to help carry sperm into the females vagina. Claspers are not the male sharks penis, but instead are an external appendage used to deliver the sperm into the female during copulation. Claspers are a pair of modified pelvic fins, which can be seen in the left image below.
Image Provided By: Earth Touch News Network
Image Provided By: The Guardian
For more information on pelagic shark reproduction, please visit Breana Goldman's website, Section 4: https://spark.adobe.com/page/ZswijPcJtNIv4/
Buoyancy
In order for great whites sharks to remain buoyant in the water column, they utilize a variety of methods in order to do so. As white sharks lack a swim bladder, which most fish use to remain buoyant, these predators use other physiological features to remain light, such as their cartilaginous skeletons, pectoral fins, and oily livers. Great white sharks have larger livers than compared to other fishes, as they account for around 30% of the sharks total body mass. These oily livers contain a compound called squalene, which helps the shark remain buoyant due to it having a specific gravity of 0.855. Squalene also has an extremely low density making it lighter than water, overall helping the shark remain light when swimming throughout the water column.
Image Provided By: Shark Lab
Great white sharks also utilize their pectoral fins to help keep them from sinking. Great white sharks use a method called dynamic lift, where the pectoral fins help create lift from the water underneath them. The white shark however must keep swimming in a forward direction in order for this method to work, similar to how a bird must remain in flight for it to remain in the air. The pectoral fins are not the only fins utilized by white sharks for lift, but also their caudal fin is used. Rapid, thrusting movements provided by the caudal fin help the white shark propel forward and generate a current for the pectoral fins to generate lift. Great white sharks also use
Image Provided By: The Monterey Bay Aquarium
their cartilaginous skeletons to remain buoyant in the water column. As mentioned in the "Skeleton" section prior, white sharks have skeletons made of cartilage instead of bone. Bone is twice as dense as cartilage, so having an overall lighter skeleton helps these sharks remain light in the water. Due to this lighter skeleton, white sharks also expend less energy which helps them not tire out and sink.
digestive system
Since great white sharks are apex predators, they have little time to chew and digest their food, as they mainly take large bites of their prey or swallow it whole. Pieces of prey such as bones cannot be digested, so they are vomited by the shark. Due to this aggressive diet, white sharks have a U-shaped stomach filled with powerful enzymes and acids used to help break down food. The broken down food then makes its way to the spiral valved intestines through the pyloric valve, which connects the intestines to the stomach. Sharks, unlike other animals, have a spiralized intestine with has a coil-like shape. Sharks have this intestine shape due a spiralized intestine having a larger absorbent surface. In the spiral valved intestines, the food begins to digest and nutrients are absorbed. Sharks also have a rectal gland that is used to remove excess amounts of salt from their food. After the the nutrients are absorbed and the salt is removed from their food, excess material is removed from the body through the anus.
Image Provided By: Enchanted Learning
Respiratory system
Like all fishes, great white sharks have gills. This respiratory organ helps the shark extract oxygen from the water. Not only do the gills filter oxygen, but they also extract carbon dioxide from the water and expel it out of the body in the form of a waste product: urine. After the water flows over the gills and then moves into the blood stream, small capillaries allow the transport of this oxygen throughout the entirety of the sharks body. Great white sharks also have five gill slits, where other species of shark can have up to seven: like the Sevengill shark.
Image Provided By: Marc Henauer
Have you ever heard the saying, "A shark must always stay swimming or else it will die."? Although this is true for some species of shark, like the great white and other pelagic sharks, not all shark species need to move in order to exchange oxygen. Unfortunately, this is true for great white sharks as they need to constantly swim in order to allow water to pass over their gills in order to extract oxygen. Some sharks on the other hand have spiracles, which help circulate water over the gills even while they remain sessile on the seafloor. I like to think of these organs as propellers, constantly spinning water over the gills.
Image Provided By: My Modern Met
circulatory system
The circulatory system of great white sharks is very simplified, as the main organs within the circulatory system are the ventricle and the auricle. Within the sharks body, blood moves from the ventricle to the aorta where it then moves to the branchial arteries. These branchial arteries can be found inside of the gills, where the blood becomes oxygenated through the shark respirating. After the blood absorbs the oxygen from the gills, it then moves to the dorsal aorta.
Image Provided By: Cardiovascular Is Cool
The dorsal aorta then moves the oxygenated blood throughout the body to the sharks organs. After the oxygenated blood has moved through all of the sharks organs, it then moves to the venous system to flow back to the heart using the cardinal veins.
Image Provided By: Sharks101
Thermoregulation
Image Provided By: Shark Watch SA
Most shark species have a body temperature that remains constant to the temperature of the water surrounding them, where great white sharks do not do this. Great white sharks, like other lamnid sharks, sustain a higher body temperature as they have a heat-retaining system: or counter current heat exchange. The heat-retaining system is comprised of red muscle, which the sharks use mostly for swimming. These red muscles are connected to the sharks circulatory system. Veins and arteries called the "rete mirabile" are responsible for connecting this red muscle to the circulatory system. When the red muscles are used, heat is generated.
This heat energy moves through the veins and arteries, or rete mirabile, where it then moves throughout the entirety of the sharks body through the bloodstream. This efficient movement of heat helps keep great white sharks warm in the frigid waters they call home. Great white sharks are able to keep their internal body termperature at +/- 15 degrees Celsius when compared to the external water temperature surrounding them.
For more information on pelagic shark thermoregulation, please visit Breana Goldman's website, Section 1: https://spark.adobe.com/page/ZswijPcJtNIv4/
Countershading
When you look at a great white shark, you can distinctly see that the shark is grey on the dorsal side of its body and is white on the ventral side of its body. This coloration is called countershading. Countershading is a type of coloration that can be seen frequently amongst many species of pelagic sharks as it serves a form of camouflage. Now you may be asking, "Why does a fierce predator like the great white shark need to camouflage? They don't have any predators.". Well, great white sharks don't necessarily camouflage to hide
Image Provided By: Jonathan Bird's Blue World
from predators, but instead use this camouflage to stay out-of-sight from their prey. Countershading allows great white sharks to remain nearly invisible from all directions. When you are swimming above a white shark and are looking down at it, the dark grey coloration helps the shark blend into the dark depths below. When you are swimming below a white shark and are looking up at it, the white coloration along its belly matches the sunlit water above. Great white sharks are nearly invisible due to this coloration, as darker colors on their body help to absorb light traveling from the waters surface. On the other hand, the lighter colors on the shark help amplify and reflect the dim light coming from the bottom.
Image Provided By: The World of Animals
Image Provided By: Adventure Bay Charters
These two images provide a general example of what countershading looks like when you are in the water with a great white shark. In the image on the left, the distinct dark grey to white coloration can be seen when viewing the shark from the dorsal to ventral side. Looking at the image on the right, we can truly see how countershading helps the shark both blend into the water by obscuring light, but how countershading can also disguise the shape of the sharks body.
SOurces
Reproduction:
Edmonds, Molly. “How Great White Sharks Work,” May 19, 2008. https://animals.howstuffworks.com/fish/sharks/great-white5.htm.
Digestive System:
Enchanted Learning “All About Sharks!” Shark Digestion - EnchantedLearning.com, 2018. https://www.enchantedlearning.com/subjects/sharks/anatomy/Digestion.shtml.
Respiration:
Castro, Joseph. “Must Sharks Keep Swimming to Stay Alive?” LiveScience. Purch, May 29, 2013. https://www.livescience.com/34777-sharks-keep-swimming-or-die.html.
Circulatory System/Thermoregulation:
Atlantic Sharks. “Physiology.” Atlantic Sharks. Accessed December 21, 2020. https://www.atlanticsharks.org/fr/about-sharks/biology/physiology/.
Thermoregulation:
Wcisel, Michelle. “Shark Cage Diving Blog: Marine Dynamics.” Marine Dynamics Shark Tours, 2012. https://sharkwatchsa.com/en/blog/category/482/post/987/shark-fact-29-02-2012/.