learningabtsharks

[learningabtsharks]

As stated in my "The Anatomy of Sharks" post, sharks are cartiliganous fish. Cartiliganous fish are a class called, "Chondrichthyes." This class is divided in two, the subclasses of it are called, "Holocephali," and "Elasmobranchii." Sharks are elasmobranchs, alongside rays and a few other species.

[learningabtsharks]

[learningabtsharks]

The Anatomy of Sharks

Reproductive information will be in another post, hidden completely behind a cut.

Movement

 Sharks are a cartilaginous fish, meaning their skeleton is entirely comprised of cartilage, not bone. Because of this, their skeleton is more light weight, making it easier to remain afloat. It also allows much more flexibility.

 When it comes to the majority of fish, most use a swim bladder to remain buoyant. Sharks, however, do not have a swim bladder, this makes them heavier than water. Sharks use their large livers, fins, and the aforementioned cartilaginous skeletons.

 Sharks use their fins to create dynamic lift, in a method similar to airplanes. (This means if they stop swimming, they stop floating.) Due to their bodies bulk and the size of their fins, this alone isn’t enough to keep them afloat. 

 Sharks also must use their massive, oil-filled livers. The oil in a sharks liver is called squalene, which is lighter than water. This increases the sharks  buoyancy, enabling them to remain afloat.

 Sharks skin is made up of many platelike scales, called placoid scales, or dermal denticles. Placoid scales are v-shaped, which reduces drag and makes swimming more efficient. These denticles also prevent marine growth, such as algae and barnacles, due to the irregular surface. Female sharks skin is up to three times thicker than male sharks.

Gills

 Sharks breathe through their gills, just as other fish do. They take in water through their mouth, which passes through their blood rich gills. Blood vessels extract oxygen from the water as it passes by. Carbon dioxide waste from their blood is expelled through the gill tissue as well.

 Species that are less active when it comes to swimming use a method called buccal pumping.

 Merriam-Webster says buccal means, “of, relating to, near, involving, or supplying a cheek”. LINK

 Sharks that are not capable of buccal pumping use something called ram ventilation. (These sharks are called obligate ram ventilators.) These species swim at a quicker pace with their mouths open in order to pass water over their gills.

 Sharks that are capable of buccal pumping pull water into their mouths via their cheek muscles, passing the oxygenated water they need over their gills without swimming.

 Sharks who respire like this have spiracles, which are gill openings behind their eyes that enable them to take in the water they need. Like a snorkel.

Senses

 The lateral line system is an organ that enables the majority of fish to detect minute vibrations in the water. In sharks, lateral line canals are just beneath the skin of its snout and along the sides of its body. Lateral line canals are full of tiny hair-like structures, as well as fluid. When vibrations reach the hair-like structures, they move, sending signals to the brain. These signals help the shark in pinpointing the placement of something else in the water.

 This system also detects odor plumes, which are a complex structure created when odor molecules are released from their source and moved. This enables sharks to locate prey and other mates.

  A sharks sense of smell and it’s lateral line are heavily intertwined. If their lateral line is inhibited somehow, they will find it difficult to detect odor plumes, even if their actual nose is perfectly fine. 

 The sharks nasal cavities have two openings, an entrance point for water, and an exit point for water. Sharks pull water into nasal sacs and over folds of tissue. A sharks nasal cavities are quite large, giving it more time to sort out the scents it picks up. The sharks brain will then analyze the smells, matching them to it’s prey, or even those of possible mates.

 The lateral line of a shark could be considered an extension of the sharks ear, as both use hair cells to assist it in keeping it’s balance and are attuned to the frequencies one would associate with underwater sounds.

 There are small openings on both sides of sharks heads, leading to the inner ear. The sharks ear is a group of ducts and sacs filled with endolymph, called a membranous labyrinth. Endolymph is simply what the liquid filling the ducts and sacs of the labyrinth is called, in sharks this is mainly sea water that enters through its ducts. These ducts are protected by the cartilaginous labyrinth surrounding it, a set of canals filled with fluid.

 Through the endolymphatic ducts, is the sacculus, the lagena, and the utriculus. These are lined with the aforementioned hair cells, which detect vibrations in the water. For hearing, there is an even longer hair cell, called a klinocilium. This hair cell extends into something called a cupola. The cupola of a shark is slightly exposed, and jelly-like. Sound vibrations in the water cause the cupola to wiggle, which the klinocilium picks up on. The klinocilium transmits these signals to the brain.

 The cartilaginous tubes in a sharks ear are only able to pick up vibrations that are parallel to it. However, there are three of them. Together, they detect vibration in all directions. As a shark loses balance, the fluid within its ears slows down. The hair-cells feel this, and transmit signals that enable the shark to correct it’s balance.

 Sharks skin is highly sensitive

 Sharks do not have color vision, but as far as fish go, their eyes are quite good. They’re still able to process focused images. Most fish have rod only retinas, made for low light levels. Sharks have both rods and cones, cones being the ones responsible in higher light levels. (It’s worth noting the light levels where both rods and cones are active are called, “Mesopic”.) This is distinctly similar to human eyes. The part of a sharks brain that coordinates movement in regards to visual input is similar in size to that of a humans. 

 While there are quite a few similarities, there are also a few glaring differences. For instance the presence of a reflective layer, called the tapetum lucidum, at the back of a sharks eye, which light bounces off of, allowing sharks to analyze the light twice over. This is especially helpful in lower light levels.

 Another difference is the way our eyes focus light. While humans have muscles that control the shape of our lens to focus light, sharks have muscles that push and pull the retina. This manner of focusing light is quite similar to the focusing of a camera.

 While all sharks have rods and cones, some have more rods, and some have more cones. Deep water species will have far more rod photoreceptors due to the low light conditions.

 Sharks sense of taste isn’t nearly as adapted as all of their other senses, due to the fact it is not necessary for survival. Their taste buds are in their mouth, as opposed to ours, which are in our tongue. Sharks have many pressure sensitive nerves in their teeth.

On top of everything else, sharks are also capable of sensing minor electrical fields. Every living thing gives off a very small amount of electricity, via the brain, muscle movement, or even the heart beat.

 Sharks have receptors all along their head and snout. The receptors are jelly-filled tubes that open on the surface of the skin, called the ampullae of Lorenzini. The jelly within the tube is highly conductive, and when it picks up on electricity, it transmits it to the bulb that is at the end of each tube. The electric signal activates nerves, and sends the resulting signal to the brain.

 These sensors are so sensitive they can detect muscle contractions of prey, and it is theorized that sharks detect the earths geomagnetic field and use it to navigate in the open ocean. These electrosensors have a very minute range due to the incredibly weak electrical impulses of usual prey.

 Sharks use this sense to locate prey that is hidden, or from far away. They pick up on the muscle contractions of other fish, like that of a fish that is wounded and struggling.

Diet

 All sharks are carnivores, with one exception. This exception is the bonnethead shark, which is an omnivore.

 When it comes to sharks, their hunting grounds, hunting methods, and diet all vary wildly. Their teeth match this variety.

 A shark with flattened teeth, such as the horn shark or nurse shark, uses them to crush their food. The structure of the teeth make it easier to crush shells.

 A shark with needle like teeth would be very effective at gripping more evasive prey.

 The Great White Sharks lower teeth are pointed, while its upper teeth are triangular. Their teeth have serrated edges, enabling them to slice up their prey into fun-sized pieces

 Sharks teeth are usually used for hooking prey, crushing, or slicing. Sharks bite force being as immense as it is, plus a lack of a tough jaw bone means that teeth often break off whilst feeding and other activities. These teeth are replaced by those in reserve rows.

 Depending on the species, sharks can have up to fifty rows of teeth at a time. When a shark loses a tooth, its gums push forward the teeth in the reserve rows like a conveyor. A sharks tooth can be replaced in under two weeks.

 In most species, the upper jaw is fully and firmly connected to the skull, and it is the lower jaw that moves. With sharks, that isn’t exactly the case. Sharks move their entire mouths to catch their prey. Not only can they move their lower jaw, they can move their upper as well.

 There are sharks that are bottom feeders, and there are those that are filter feeders. There are those with incredibly specialized hunting methods, and those that eat just about anything.

Reproduction

LINK

LINKS

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https://www.dcnanature.org/shark-biology/

https://science.jrank.org/pages/1246/Cartilaginous-Fish.html

https://www.fossilguy.com/gallery/vert/fish-shark/remnant.htm

https://www.sharks-world.com/why_do_sharks_have_cartilage/

https://www.sharksinfo.com/buoyancy.html

https://animals.mom.me/oily-liver-shark-work-7894.html

https://www.thoughtco.com/placoid-scales-definition-2291736

https://ocean.si.edu/ocean-life/sharks-rays/sharks

https://www.scientific.net/AMR.79-82.977

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http://www.elasmo-research.org/education/topics/p_liver_size.htm

https://www.dkfindout.com/us/animals-and-nature/fish/how-fish-breathe/

https://www.livescience.com/34777-sharks-keep-swimming-or-die.html

https://www.merriam-webster.com/dictionary/buccal

https://poseidonsweb.com/how-fish-breathe-ram-ventilation-buccal-pumping/

https://www.sharksider.com/spiracles/

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https://www.sharksinfo.com/lateral-line.html

https://www.britannica.com/science/lateral-line-system

https://www.annualreviews.org/doi/pdf/10.1146/annurev.en.37.010192.002445

https://www.pbs.org/kqed/oceanadventures/episodes/sharks/indepth-senses.html

https://www.sciencedaily.com/releases/2007/05/070529140610.htm

https://jeb.biologists.org/content/210/11/iii

https://www.sharksinfo.com/hearing.html

https://animals.howstuffworks.com/fish/sharks/shark-senses2.htm

https://www.ncbi.nlm.nih.gov/books/NBK10792/

https://www.epicdiving.com/shark-vision/

https://azretina.sites.arizona.edu/node/353

https://www.cis.rit.edu/people/faculty/montag/vandplite/pages/chap_9/ch9p1.html

https://www.enchantedlearning.com/subjects/sharks/anatomy/Senses.shtml

https://www.shark.ch/Information/Senses/index.html

https://www.sharktrust.org/shark-senses

https://phys.org/news/2018-02-sharks-animals-evolved-electroreception-theirprey.html

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1578252/

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https://www.discovermagazine.com/planet-earth/these-first-known-omnivore-sharks-eat-seagrass

https://www.sharksinfo.com/jaw.html

https://www.bradenriverdentist.com/a-guide-to-shark-teeth/

https://cimioutdoored.org/shark-teeth/

https://animals.howstuffworks.com/fish/sharks/shark4.htm

[learningabtsharks]

The Anatomy of Sharks - Reproduction

This post could be considered NSFW, but I just consider it a massive part of sharks migratory and behavioral patterns. I put it in a seperate post, just in case people would rather not read about it.

Reproduction

 When it comes to reproductive strategy in evolution, there are two ways. There is r-selection, which is a lot of offspring in order to increase the chances of some surviving to reproduce. This method is used by species whose environment is harsher than others. Then, there is k-selection, this one being having few offspring, of which are stronger. This is used by those in more stable environments.

 R-selection takes less energy, and the organisms tend to be smaller. They also tend to have a lower life expectancy. They mature rapidly. Reproduction occurs only once.

 K-selection takes more energy, and are generally larger in size. Fewer offspring are produced, but they are stronger. Their life expectancy is longer, and they mature much slower. Individuals reproduce multiple times. Sharks are in this variety.

 Sharks have nurseries in which their young will be, whatever method they reproduce in. A shark nursery is a steady place of sustenance for a young shark to grow.

 In sharks, males have a pair of claspers. Females have oviducts, which lead to the womb. Male sharks will insert their claspers into female sharks oviducts, then they will fertilize the female sharks eggs. In order to stay with the female in the open ocean, males will bite, utilizing female sharks thicker skin.

 The gestation period for sharks is anywhere from one to three years.

 After fertilization and gestation, sharks reproduce in multiple ways. These ways being, viviparity, oviparity, ovoviviparity, and asexually.

 Viviparity is the same method which humans use, where an embryo develops inside the females uterus, and is born alive. The embryo is sustained via an umbilical cord.

 Oviparity is when the egg develops seperately from the female, sustaining itself with the eggs food supply. Female sharks will search for a safe place to leave the leathery pouch in which their young will develop.

 Ovoviviparity is similar to oviparity, in that eggs are lain. However, the eggs remain inside the female until they hatch or are ready to hatch. They are sustained on the eggs food supply, or via their siblings.

 Female sharks are capable of reproducing asexually. Due to the lack of fresh genes, the pup is a clone of the mother. Asexual reproduction in sharks has only been observed in captivity, but it is theorized this method would be used if a female shark could not find a suitable male.

 Mother sharks do not tend to their young, but they do insure they are delivered to their nursery. Pregnant female sharks will return to the same place they were born to give birth.

LINKS

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http://www.bio.miami.edu/tom/courses/bil160/bil160goods/16_rKselection.html

https://gilisharkconservation.com/a-full-guide-to-shark-reproduction-and-baby-sharks/

https://www.sharksider.com/four-unique-ways-sharks-reproduce/

https://www.researchgate.net/publication/232804870_Shark_nursery_areas_Concepts_definition_characterization_and_assumptions

[learningabtsharks]

I’m trying to learn about sharks right now, so I’ve decided to write about my learning as I go along. I find it’s much easier to retain information when you write it down. 

Feel free to ask me questions, because while I may not have the answer when you ask it, I’m happy to find it for you. 

I’m planning on putting together profiles, of sorts, about different sharks. Feel free to request one in my ask box!