Welcome back to another Finn Friday! Today we are going to learn about a pretty unusual shark. When you typically think of sharks, you think about the top predator of the ocean, which is true in most cases. However, the shark we are going to learn about today is actually considered to be parasitic! How crazy is that?! Even crazier though is the fact that they glow! Man, this little shark is cool. Without further ado, let’s learn all about the amazing little Cookie Cutter shark!
Where do they live?
Cookie cutter sharks are pelagic, meaning they live in the open ocean. During the day they stay lower in the water column (1,000 meters or more below the surface), but migrate to the upper column and surface at night. They can be found in tropical and temperate waters around the world. They are most commonly found near islands.
How long do they live?
Currently, we don’t really know how long cookie cutter sharks live, but we do know a little bit about their life history. Cookie cutter sharks are ovoviviparous, meaning they give birth to live pups, but are encased inside of an egg while inside the uterus. Basically, while they are in the egg in the uterus, they feed on the egg yolk instead of being attached to the mother shark’s digestive system through a placenta. They are hatched/born after about 12-22 months. Cookie cutter sharks typically have 6-12 pups per litter. They reach reproductive maturity at around 1-1.2 feet for males and 1.2-1.4 feet for females. The maximum length for males is around 1.3 feet, while the maximum length for females is approximately 1.6 feet.
What do they eat?
Now we get to chat about how exactly the cookie cutter shark is a parasite. Basically, cookie cutter sharks bite chunks out of bigger fish, sharks, and marine mammals, but don’t kill them. They do this by attaching to their prey by suctioning to the animal with their lips and grabbing hold with their upper teeth. Once they are attached, they spin their body around and use their serrated bottom teeth to cut out a round plug of flesh or blubber, which they then swallow whole. They have also been known to eat smaller squid, fish, and crustaceans as well. Now, this is going to sound really weird, but they also eat their teeth. Like other species of sharks, they regularly lose and replace their teeth to make sure they are always super sharp and in good condition, but other sharks don’t really eat their own teeth. Scientists believe that cookie cutter sharks do this because they live in a pretty nutrient-poor part of the water column. Eating their own teeth is believed to help them maintain calcium levels in their bodies.
What do they like to do?
We don’t know a whole lot about what the cookie cutter shark does on a daily basis because they live so far down in the water column most of the time, but I thought I would take this time to tell you all about how they attract their prey. Like I said before, cookie cutter sharks glow! Basically, the entirety of the ventral surface (i.e. belly) of the cookie cutter shark, with the exception of a dark collar around its gill area, is filled with a network of tiny light-producing organs called photophores. These photophores make their bellies glow green! Now, their glowing green belly and the non-glowing band can make the cookie cutter shark look like a smaller fish from a distance, luring their larger prey to them.
Thanks for learning with me! Aren’t cookie cutter sharks so cool? I still can’t get over the fact that they can glow. What did you find most interesting about the cookie cutter shark? Let me know below!
Sources:
https://oceana.org/marine-life/sharks-rays/cookiecutter-shark
https://www.sharks.org/cookiecutter-shark-isistius-brasiliensis
https://www.floridamuseum.ufl.edu/discover-fish/species-profiles/isistius-brasiliensis/
https://marinebio.org/species/cookiecutter-sharks/isistius-brasiliensis/
https://ocean.si.edu/ocean-life/sharks-rays/cookie-cutter-shark
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