Sharks are the ocean’s top predators. They’ve evolved into over 400 different species and they have varying diets and behavior. There are a lot about sharks that are unknown to many people. Understanding sharks in general is very important to understanding the individual species of sharks.
Sharks fall into a subclass of fish called elasmobranchii. Sharks in the subclass have skeletons made from cartilage and they have five to seven gill slits on the sides of their heads. This is different from many fish, who have skeletons made from bone and 1 gill on each side of their head. Sharks use the gills on the side of their head to filter oxygen from the water to breathe. They have multiple rows of teeth that fall out and grow back routinely. Even though they all have rows of teeth, some are serrated like a razor and others have triangular teeth.
Sharks can be found in both deep and shallow waters. They all migrated vast distances to feed and breed. There are some differences between them. Some shark species are solitary while others hang out in groups. Some sharks are known to congregate in large groups to socialize. Scientists still are confused about a lot of the behaviors of sharks. They’re still trying to pinpoint how long sharks live and they’ve only studied a fraction of shark species. Notably, the Greenland shark is the earth’s longest living vertebrate and it has lived to be 272 years old.
Although sharks are known for their human attacks, humans are not their preferred food. Shark attacks have increased steadily since the 1900s but this might be the result of better recording and a rising human population. Shark attacks are still very rare and a beachgoer has a 1 in 11.5 million chance of being bitten. This means they’re more likely to be struck by lightning or die from drowning than from a shark attack. Even though shark attacks are seen in horror movies sharks bite people out of curiosity, defense, or confusion.
Sharks are not a significant threat to humans but humans are a threat to them. Humans are responsible for the drastic decrease in shark populations. This decrease occurs due to overfishing. 100 million sharks are killed each year and they’re mostly to supply expensive dishes. Fisheries that catch whole sharks often cut off the fins and dump them back into the ocean where they bleed out or drown. This is done to save space on the boat and avoid surpassing fishbone braids but it’s very deadly to the shark population. Many fisheries have outright banned shark fishing.
Another thing that often impacts sharks are rising water temperatures in coastal developments. They contribute to the shrinking shark populations because the coastal developments are destroying mangroves in coral reefs. These are places that are used for breeding, hunting and protecting young shark pups. A drop in numbers is bad for sharks, but it could also be bad for ocean health in general. Because they’re top predators of the ocean, they are critical for balancing the food web.
Here’s more information about shark anatomy.
Sharks possess an internal skeleton just like other fish. A shark skeleton differs from that of other fish because it’s made of cartilage. Cartilage is a strong and durable material but it’s also lightweight and relatively flexible. The characteristics of cartilage Aid in the general movements of the shark in a variety of ways. Cartilage is much lighter than bowing and helps fish I keep from sinking. Since a shark has no swim bladder like other fish, and it relies on its cartilage skeleton for buoyancy. This allows the shark to turn the tighter radius than other fish. Cartilage found in the jaws of backbones are parts that require more strength than the cartilage in their fins. These areas are strengthened with calcium salts that form a calcified cartilage that has similar strength characteristics of bone without the weight.
Like the rest of the skeleton, the shark’s skull is also made mostly of cartilage. The shape of the skull can vary from the classic shape of a rounded skull to a broad and flat shape of a hammerhead shark. The most variable aspect of the shark’s skull is the jaw. The jaw can be attached to the cranium in different ways and this is related to the method in which the shark feeds. The most common shark jaw found in modern sharks allows the full job to swing down and forward in order to swallow large prey.
Sharks have a basic eye structure that is found in all vertebrates but they have some modifications. Shark eye has a reflecting layer called a tapetum lucidum that’s located behind the retina. Essentially this structure consists of a layer of parallel, plate-like cells filled with silver guanine crystals. These crystals reflect light that has already passed through the retina and redirects it back to restimulate the retina as it passes out through the eye. This boosts the visual signal in low light levels, giving sharks high visual acuity.
Another modification in their eye that’s found in some sharks is the presence of a nictitating membrane. The structure is a denticle that’s covered in a membrane that protects the eye. It closes when the shark passes close to objects and also during biting or feeding to stop the eye from being punctured or scratched.
All sharks have five to seven pairs of gills on the sides of their head. Gas exchange occurs at the gills and oxygenated water must always be flowing over the gill filament for respiration to occur. The water enters through the mouth of the animal, into the pharynx and over the gills. It exits through the gill slits. Respiratory gas exchange takes place on the surface of the gill filament as the water passes over and out the gills.
Some sharks have spiracles which are special gill slits located just behind the eyes. These gill slits supply oxygen directly to the eyes and brain of the shark. Bottom-dwelling sharks like the angel sharks use this extra respiratory organ to breathe while at rest on the seafloor. It’s also used for respiration in the shark’s mouth while they’re eating.
Gill slits are individual openings to gills that look like multiple gill arches. They lack a single outer cover. These skills are characteristic of cartilaginous fish like sharks and rays as well. In contrast, bony fishes have a single outer bony gill covering called an operculum. Most sharks and rays have five pairs of gill slits, while a few species have six or seven pairs. These gills are placed in a row behind the head. While the shark is moving, water passes through the mouth and over the gills in a process known as ram ventilation. While they’re at rest, most sharks pump water over their gills to ensure a constant supply of oxygenated water. A small number of species have lost the ability to pump water through their gills and must swim without rest.
Shark teeth are not large permanently lodged in their jaw, but they are attached to a membrane known as a tooth bed. The tooth bed membrane is similar to a conveyor belt because it moves the rows of teeth forward as the shark grows. This means the older teeth in the front are replaced when they become damaged, falling out or worn down. It is not uncommon for shark teeth to be found lodged in large prey or loose on the ocean floor. The shape, number and appearance of shark teeth varies considerably among shark species and it can be one of the most important features for species identification. Tooth appearance can also differ between the upper and lower jaw, and from front to back within any shark.
The blue shark is a good example of how teeth differ between the upper and lower jaws. The upper teeth are triangular and curved with serrated edges and overlapping bases, while the lower teeth are more straight and slender with finely serrated edges. The teeth of the porbeagle and mako shark are similar in the upper and lower jaws. The porbeagle has smooth edged teeth with lateral denticles while the mako shark has more slender teeth with lateral denticles.
Shark skin feels like sandpaper because it has small rough placoid scales. These skills are known as dermal denticles. As a result their skin is often dried and used as leather product or sandpaper. And I chords scales consists of basal bony plates buried within the skin and a raised portion that is exposed. These tentacles are homologous and structure two teeth which sport gets asked in a rough feeling. Dermal denticles are small tube-like structures on the skin and they’re important because they form a protective barrier and a the shark when they’re swimming.
As the shark grows and grows more placoid scales. These scales help the Sharks win more quickly because their streamlined shapes help decrease the fiction of the water flowing along the shark’s body. It channels of water through the grooves and their skin. The shark skin is so rough that contact with it can injure the prey. Many will never get close enough to touch a shark, but if you were to you feel the roughness of their skin and the teeth like construction of it.
The bends are one of the most important parts of the outer body of a shark. Sins are used for stabilizing, steering, lift and propulsion. Each of their fins or using a different way. There are one or two fins along the dorsal midline called the first and second dorsal fin, and these are anti-roll stabilizing fins. Pectoral fins are located behind the head and they extend outward. These fins are used for steering during swimming and can help provide the shark with lift. Then, there are pelvic fins that are found near the cloaca and these are also stabilizers. Anal fins may be absent but if there are present are located between the pelvic and caudal fins.
The caudal peduncle is a feature that might be found just ahead of the caudal fin. The caudal fin has both an upper and lower lobe it can be different sizes and the shape varies between the shark species. The primary use of the caudal fin is to produce the most thrus, and this is the force that would make the shark move downwards. Lift to counter this force is produced by the pectoral fins and the shape of their body working together. The fins of the shark are all perfectly placed so that they can provide the shark with the advantage to live and hunt in the ocean.
Each shark has a tail that’s adapted to its physiology, its surroundings and it’s lifestyle. This means there is great diversity in the types of tales on all of the sharks. Each one is composed of a precaudal pit and an upper and lower lobe. In some cases, the spine extends to the tip of the superior fin so the tail is called heterocercal. On the body the tail functions as a propeller. By swinging it forward and backwards, the shark can advance in the water. It pushes the water around their fins to create a movement that produces elevation. The thrust, velocity and acceleration of the swim depends on the shape of the caudal fin, but with some adaptations, the tail has other purposes that are related to those other than swimming. For example, in the cookiecutter shark, there is bioluminescence in the upper and lower lobes of the tail that serve to attract prey.
Sharks are amazing creatures, but their populations are being threatened. Coastal developments, garbage in the ocean, and climate change have all negatively impacted sharks. Even though those things are bad, the largest threat to sharks is overfishing. Because they’re hunted for their fins and their skin, their populations are rapidly declining. Consider volunteering with organizations that help sharks or recycling so that you can minimize your waste that ends up in the ocean.