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Sharks

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Nora Teter

on 6 March 2015

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Transcript of Sharks

Sharks

An anatomical overview
Skin
.
Interestingly enough, these denticles don't grow as the shark grows, but rather grow independently as necessary
Sharks don’t have bones, and thus rely on dermal denticles to help retain their body shape.

These denticles act as both a form of defense by, but also and allow sharks to swim more efficiently, as they streamline the animal.
Jaws and Teeth
The jaws of a shark are not attached to its skull. Furthermore, the upper and lower jaw can work independently without the other moving, this gives the shark a very powerful pull and bite.
Sharks have many rows of teeth, the amount is variable between species.
The shape of a sharks teeth are also variable between species.
Taste
The gustation organs of a shark are not as adaptable as the other sensors of a shark, however this makes sense as taste is not used to locate prey.
Sharks have taste buds which line their mouth and a gullet. When they bite an object, signals are passed to the brain to determine whether the prey should be rejected or consumed. So many people survive shark attacks, as the shark almost always spits the human out when it realizes it's not shark-food.

Because the chemistry of smelling and tasting both depend on dissolved material, these two senses complement each other.
Olfaction in sharks is a crucially important sense because it’s used when detecting prey.
The sensory epithelium consists of microvillous sensory and ciliated support cells that form the superficial layer of the olfactory rosettes contained within large bilateral olfactory cavities on the ventral surface of the snout. (Kleerekoper 1978; Zeiske et al. 1987).


In carcharhinid sharks (or requiem sharks), the water flow over the olfactory rossette is produced by the water pressure difference between the incurrent and excurrent nares while a shark is propelled during swimming .
Smell
Incurrent vs excurrent aperatures, that lead to respective nasal cavities (nares).
Olfactory stimuli evoke a klinotaxis behavior in the nurse sharks. As you can see in this video, the shark is is searching the ocean floor to locate the source of the food.
On the other hand, when lemon sharks are presented with a source chemical stimulant, they respond with accelerated
swimming and a strong rheotaxis behavior. (Mathewson and Hodgson 1972; Hodgson and Mathewson 1978; Kleerekoper 1978).
Klinotaxis-
a wavering side - to - side motion of the head occurring as an organism moves forward in response to a source of stimulation.
Rheotaxis- an oriented movement of an organism in response to a current.
Behavioral studies now show that the blocking of nasal passages can eliminate the ability to locate the source of an odor, just like in humans.
Once a chemical has fit into a receptor cell, an electrical charge is induced in that cell and is then transmitted via the nervous system to the brain. It is there where the stimulus is interpreted.
The difference between the two senses - smell and taste - lies in the amount of chemical compound sampled by an organism.
There is a variety of shape specific receptors because different chemicals have differently shaped molecules. The preciseness of the fit between the chemical and receptor dictates the intensity of smell
Because a sharks olfactory organs aren't connected to the respiratory passageways, their "nostrils" are called nares.
The olfactory organ is spherical in shape and is composed of several parallel plates (lamellae) that are studded with chemoreceptors.
The olfactory sensitivity in sharks is known to be incredible, due to the compact arrangement of the receptors in the sharks olfactory organ.
People actually underestimate the smelling abilities of a shark. Lab experiments on isolated olfactory lamellae of skates revealed responses to concentrations as low as 10-14 moles per litre of water for serine (1 molecule of serine in 1015 molecules of water). This is comparable to finding a golf ball in Loch Ness
Due to their astounding olfactory acuity and zig-zag hunting behavior, it's generally assumed that sharks compare the intensity of scent received by each nare. By continually adjusting their course according to whichever nare received the strongest concentration of stimuli, a shark could quickly locate the source of odor. (Kajiura, 2011)
Mechanoreception
There are two sensory organs in sharks which detect sound and movement: the lateral line and the ears.
The ears of a shark are located behind its eyes on either side of its body
Shark flesh has a density that is similar to that of the surrounding sea water. Because of this, vibrations emitted by sound are able to ripple the along the ear canal and into the ear of the shark.
The water that moves through the sharks head is acoustically transmitted, and this stimulation produces nerve signals.
The lateral line consists of fluid filled canals located right under the skin, running from the head down the side of the body.
The lateral line is very sensitive to low frequency vibrations, and responds to variations in water currents and pressures from underwater sound and allows the shark to detect both the direction of the movement and the amount from great distances.
The lateral line, in addition to other acute senses, is one of the main reasons why sharks can easily detect prey from far distances.
Magnetoreception
The Ampullae of Lorenzini is the organ that some sharks use to detect weak electrical fields from short ranges. The detection is only effective within inches, as sharks only sense bioelectrical fields in the final stages of capturing prey.

The Ampullae of Lorenzini consist of small pores and vesicles found on the head of the shark.
Many species of sharks have demonstrated the ability to sense magnetic fields.
When a shark swims through the earths magnetic field, the electromagnetic induction creates an electric field around the shark.
Differences in the earths magnetic field at different locations results in differences in the induced electrical field, this may be detectable by a sharks sensitive electroreceptors.
It's hypothesized that a permanent magnet with correct specifications could overstimulate the ampullae of lorenzini, and thus could be used as a selective shark repellent.
Photoreception
The structure of a sharks eye is very similar to that of other vertebrates. It contains a cornea, lens, retina, pupil, and iris. They have duplex retinas (retinas containing both rods and cone cells).
Located behind the retina, there is a layer of mirrored crystals called the tapetum lucidum.
The eyes of a shark are unmoveable and only some species can see in color, however they still have a very well-adapted and acute sense of vision
This provides a way for light that initially escapes detection to be detected as it passes through the retina a second time. This is the same process that allows cats to see in the dark, however the tapetum lucidum of a shark is twice as strong.
This enables the shark to see in dark and murky water.
This process defocuses the light which reduces the acuity but increases sensitivity.
The size and function of a sharks eye varies amongst species because the animals are uniquely adapted to their environments in every way.
Sharks have three eyelids, but only one can can move.
The third and moveable eyelid is called the nictitating membrane.
This third eyelid closes during feeding in order to protect the shark, making it temporarily blind while attacking.
Fins
Most sharks have eight fins
A pair of pectoral fins, a pair of pelvic fins, two dorsal fins, an anal fin, and a caudaul fin
The pectoral fins are located behind the head at the anterior end of the shark, these are used to lift and steer.
Located behind the pectoral fins are the pelvic fins. These double as claspers for males.
Some sharks have one dorsal fins while others have two, these are also used for stability.
The anal fin, which adds additional stability, is located between the pelvic and caudal fin on the bottom part of the shark.
Caudal fins are one of the most important parts of the entire shark as they propel them through the water.
Also known as the tail fin, the caudal fin consists of a lower and upper lobe.
Caudal fins can vary in shape and size per species of shark. The upper lobe is the source of most of the sharks thrusting abilities.
Because of the strength and variation of a sharks fins, sharks are one of the most well adapted swimmers in the ocean.
Body Design and Swimming Modes
Smell- a imprecise sample of a small amount of chemical stimulus that is moved through a transporter medium (like water or air).
Since both require contact between a shape-specific receptor cell and a dissolved chemical sample, they two senses are actually just different degrees of the same sense.
Taste- a sampling of a larger quantity of chemical stimulus that is more detailed because it comes into direct contact with chemical receptors.
Sandbar shark
Hammerhead sharks swim with their whole bodies, due to the attachment of muscles to many vertebrae in the spine.
Shortfin makos keep their bodies stiff and mainly move their tails. Their muscles extend deep within their body and is attached to the base of the tail, which then can be moved from side to side in a swinging motion. (sort of like a sail boat, they use their tail as a rudder)
All sharks have cartilage for their skeleton rather than bones.
This is very different from humans and most types of land animals.
Having this cartilage is what allows them to move at unbelievable speeds through the water.
Basic shape of a shark:
Torpedo shaped body that is pushed forward by a two lobbed tail at the posterior end and a mouth at the anterior end.
Yaw- sway of the body from side to side as the caudal fin propels it forward, this is minimized by thin and flat appendages projecting upward and downward from the body the dorsal and anal fins.
Roll- tendency of the body to rotate. Reduced by paired flat horizontal appendages extending outward from the sides of the body, the anterior pectoral fins and posterior pelvic fins.
Caudal fin of a whale shark
All of these fins are less flexible at the base and more flexible at the distal edges. This keeps stabilizers stiff for the shark.
Muscle
Striated muscles
There are two types of striated muscles: cardiac muscles and skeletal muscles.
Cardiac muscles have a high stamina for continuous performance, they allow the shark to swim for long distances at a steady pace.
Smooth Muscles
The skeletal muscles of a shark are subject to direct control by the brain and move on command.
Surrounding inner organs such as the stomach, intestines and blood vessels. These muscles can't be moved on command are are moved automatically.
Dorsal Longitudinal Bundles
These are some of the the names and functions of the muscular system of the dogfish shark
These aid in both up and down and side to side movements.
Ventral Longitudinal Bundles
These also aid in the side to side movements.
Lateral longitudinal Bundles
These also aid in side to side movements
Myotomes
Muscle Segments
Epi hyoidean
(h=epi hyoidean)
Helps lift rostrum
Abductor Mandibulae
Main muscle used for closing jaw
Intermandibulaes
Aids in closing jaw
Levator of Fin
Depressor of fin
Helps lift the fin
Helps lower the fin
Skeleton
Sharks don't actually have bones, but rather a cartilaginous skeleton.
Endoskeleton of a shark
The endoskeleton is separated into two categories: the axial and the appendicular
chrondrocranium- head case
The vertebral column eventually extends into the upper lobe of the caudal fin.
The axial skeleton consists of the vertebral column and the chrondrocranium.
The appendicular skeleton comprises elements that support the fins.
The skeletal elements of a shark are made of hyaline cartilage.

This is a pearly blue elastic substance covered with a thin layer of denser and stiffer prismatic cartilage. It's able to bend from side to side, yet still provide support.
These blocks of calcified cartilage fit together and form a complex structure similar to a tesserae.
This material posses around the same strength of bone, but without the added weight.
It's an amorphous material that contains no nerve or blood vessels.
Can be divided into four regions: the ethmoidal (rostrum, nasal capsule), the orbital (circular orbits that surround the eyes), the otic region (space allocated for inner ear), the occipital region (articulates the vertebral column)
Water and Ionic Regulation
Most sharks can only swim in salt water.
Osmoregulation is how an organism is able to maintain a constant concentration of water in its body, even when the outside environment would normally cause the organism to lose or gain water. Both freshwater and saltwater fish osmoregulate.
However there are two exceptions to this:
The river shark (Carcharias (Prionodon) glyphis)
The bull shark (Carcharhinus leucas)

Both of these species are able to survive in both fresh and salt water.
In sharks, the normal osmoregulation process in a salt environment consists of the removal of excess salt from the bloodstream through urine as well as the high concentration of urea and other biological solvents in the blood.
The latter allows them to absorb water from the ocean surroundings, while the former rids them of salt they continually absorb. These tasks are mostly controlled by the kidneys.
Bull sharks can adapt to fresh water because they've also adapted their process of osmoregulation.
Their kidneys can gradually adjust to the salinity of the water they're in (thus they usually travel from the ocean, to an estuary, and eventually a river) by removing more urea and less salt from the bloodstream through excess urination.
This evolutionarily useful adaptation is essentially a reversal of the normal salt-water method of osmoregulation.
Thermoregulation
Most sharks are ectothermic
They can’t control their own body temperature through their metabolism, but rather through through the surrounding water temperature.
Exceptions among this are the mackerel sharks (lamnidae, inducing the great white shark and the mako shark) and the common thresher (alopidae). They are endothermic, which means that they can regulate their own body temperature, however they’re special cases.
There is a network of blood capilaries located between the swimming muscles, which acts as a heat exchanger.
Running along the opposite direction (from gills to tail) are the thin blood vessels with the cold, oxygen rich blood.

Because of this, heat is transferred to the blood flowing into the body, simultaneously, the blood that is flowing towards the gills cools off and can't lose as much heat to an outer medium.
This is such an efficient process that hardly any body heat is lost through the gills, leaving the inside of the body 5-14 degrees celsius above the water temperature.
Heat is created through muscle activity as the shark swims. Blood is transported through the blood vessels, delivering the oxygen-depleted blood to the gills.
Since the cold blood vessels run in the opposite directions along the heated vessels, they are warmed.
Brain Organization
The brain to body ratio of a shark is larger than that of most fish, and is actually comparable to most vertebrates including mammals.
The size and complexity of the brain varies from species to species.
The sharks with the largest brain : body ratio are the dusk shark...
and the scalloped hammerhead.
Sluggish slow swimming sharks- like the angel shark - have a smaller brain : body ratio.
Both highly active species.
Partial list of brain functions
The cerebellum is responsible for body movement.

The olfactory sac (or bulb) is responsible for chemoreception.
The hindbrain is responsible for moving the head and for processing sensory information

The tectum is responsible for integrating sensory information.

The Diencephalon is responsible for regulating hormones as well as some behaviors.
The forebrain is responsible for coordinating sensory information.
It is these denticles which give sharks their characteristically 'rough' skin.

Sharks loose their teeth every couple of weeks to months, in fact it is estimated that a shark will go through 30,000 teeth in its lifetime. When a current row falls out, the next row just moves up to be first,
The size and shape generally depend on the diet of the type of shark.
Personal footage of a cow shark exhibiting klinotaxis behavior while searching for food.
Inside of a sharks eye
All species of shark move remarkably different in the water.
=
Bull shark
Tiger Shark
Great White Shark
Cow Shark
Cookiecutter Shark
Whale Shark
Sources:
Bourdon, R. J., Carrasquilla-Henao, M., Collicutt, B., Freshwater, C., McMillan, O., Messmer, A., Robinson, J. P. W., White, E. R. and Juanes, F. (2014), THE BIOLOGY OF SHARKS AND RAYS - By A. P. Klimley. Journal of Fish Biology, 84: 1266–1267. doi: 10.1111/jfb.12373
Meyer, Carl G., Kim N. Holland, and Yannis P. Papastamatiou. "Sharks Can Detect Changes in the Geomagnetic Field." The Royal Soceity (2005): n. pag. The Royal Society. The Royal Society, 22 Mar. 2005. Web. <http://rsif.royalsocietypublishing.org/content/2/2/129>.
Mallatt, Jon. "Ventilation and the Origin of Jawed Vertebrates: A New Mouth." (1995): 1-5. EBAH. Web. <http://www.ebah.com.br/content/ABAAAALNMAK/mallat-j-1996>.
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videos:
https://w ww.youtube.com/watch?v=HF6eEeM4kyM
https://w ww.youtube.com/watch?v=vWMbEHy267o&feature=iv&src_vid=qOG6gk2Ufdw&annotation_id=annotation_996165569
https://w ww.youtube.com/watch?v=qOG6gk2Ufdw
http://w ww.sharkdefense.com/Magnetics/magnetics.html
https://w ww.youtube.com/watch?v=jzZmJ536s0M
https://w ww.youtube.com/watch?v=shA9YDkBT38

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