My Science School

When one says conservation efforts to save a species have paid off, it usually means one thing a steady increase in the species population. And that's good news. Recently though conservation efforts paying off had a slightly unexpected result. What is it? Come, let's find out.

In summer, great white sharks move up the Atlantic coast of the U.S., towards New England. Their numbers normally hit the peak between August and October. But a few weeks ago, an unusual increase in human-shark encounters was evident along the U.S. East Coast, The reason? Experts believe it could ironically be due to the "conservation wins for vulnerable species". There has been an increase in great white shark numbers, which experts think is the result of continued protection. And this likely led to increased human-shark encounters too.

An important factor in the shark number increase is the fact that the number of its main prey -the seal-has seen an uptick too due to protection. Scientists also believe that the increasing encounters could be "linked to the sharks bait fish-menhaden, also known as porgies or bunkers, recovering". But they also warn that "it's tricky to figure out how much of it is increasing populations moving around as a result of changing ocean conditions from climate change.”

Though there have been instances of sharks being portrayed in pop culture as blood-thirsty, that's far from the truth. Studies have shown that sharks can mistake surfers or swimmers for their usual prey meaning many attacks could be the result of mistaken identity. Researchers say that if the number of beach-goers is anything to go by, there should be tens of thousands of shark attacks every year whereas the truth is that annual global deaths due to shark attack is five. When more sharks come close to land for feeding and more people go swimming, the encounters are likely to increase.

And with climate change experts expect "that the increase in ocean temperatures will gradually lengthen the season during which sharks are present in the northern United States". This could mean increased chances of encounters in the future. Increased vigilance and self-awareness will go a long way in minimising the risk of attacks, feel experts.

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Sharks have existed for more than 450 million years, whereas the earliest tree, lived around 350 million years ago. Not only are sharks older than trees, but they are also one of the only animals to have survived four of the five mass extinctions – now that’s impressive.

Emma Bernard, a curator of fossil fish at the Museum, says, 'Shark-like scales from the Late Ordovician have been found, but no teeth. If these were from sharks it would suggest that the earliest forms could have been toothless. Scientists are still debating if these were true sharks or shark-like animals.'

Analysis of living sharks, rays and chimaeras suggests that by around 420 million years ago, the chimaeras had already split from the rest of the group. As there are no fossils of these animals from this period of time, this is based solely on the DNA and molecular evidence of modern sharks and chimaeras. It was also around this time that the first plants invaded the land.

By the middle of the Devonian (380 million years ago), the genus Antarctilamna had appeared, looking more like eels than sharks. It is about this time that Cladoselache also evolved. This is the first group that we would recognise as sharks today, but it may well have been part of the chimaera branch, and so technically not a shark. As active predators they had torpedo-shaped bodies, forked tails and dorsal fins.   

Credit : Natural History Museum

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While the shark in Jaws was inspired by a great white shark in New Jersey, the legendary fish is far less fearsome in reality. As scientific research on these elusive predators increases, their image as mindless killing machines is beginning to fade.

Found in cool, coastal waters around the world, great whites are the largest predatory fish on Earth. They grow to an average of 15 feet in length, though specimens exceeding 20 feet and weighing up to 5,000 pounds have been recorded.

They have slate-gray upper bodies to blend in with the rocky coastal sea floor, but they get their name from their white underbellies. They're streamlined, torpedo-shaped swimmers with powerful tails that can propel them through the water at speeds of up to 15 miles per hour. They can even leave the water completely, breaching like whales when attacking prey from underneath.

Credit : National Geographic

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Baby sharks, which are known as pups, can be born in three quite different ways. First, some sharks lay eggs. We call this oviparous. The “mommy shark” lays an egg case in a good spot and swims away. The egg case, which is sometimes called a “mermaid’s purse,” can be perfectly camouflaged to blend in with the sea floor or algae. The egg includes all of the nutrition the pup will need to grow from a fertilized embryo to a fully functioning shark pup. When the pup is ready, it emerges from the egg case and is totally independent.

Second, some sharks grow from eggs–but inside the mother shark’s body. This is called ovoviviparous. In this type of reproduction, there is no placenta to link the “mommy shark” and the “baby shark.” The shark pup gets all of its nutrition from its own egg yolk, other egg yolks, or (yikes!) from eating its fellow fertilized eggs or other pups. Ovoviviparous sharks give live birth to a fully independent pup. This is how sand tiger sharks, like the ones you can see at the Greater Cleveland Aquarium, reproduce.

And third, some sharks do have a placenta and directly support the shark embryo until it is ready to be born as a pup. This is called viviparous, and is also how humans are born. When the shark pup has matured enough, it is born and swims away. This is how sandbar sharks, which you can also see at the Aquarium, have pups.

Credit : Great clevel and aquarium 

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Like almost all shark species, Great White Sharks have a highly distinctive appearance with large, torpedo-shaped bodies and a pointed snout. They have very tough skin that is covered in tiny teeth called denticles that is slate-grey to black in colour on the top of their bodies which helps them to remain camouflaged into the rocky, coastal sea floors where they are most commonly found. The underside of the Great White Shark is white and is what has led to their name. Great White Sharks have powerful, crescent-shaped tail fins that help to propel them through the water at a tremendous speed, and are aided by their pectoral (side) fins that are held out in fixed wings to prevent the Great White Shark from sinking. The large and highly characteristic dorsal (back) fin of the Great White Shark is used to help them to steer through the water, along with diving and helping them to balance. One of the most characteristic features of the Great White Shark is their jaw. Their mouths are filled with up to 300 serrated, triangular teeth that are arranged in rows and are replaced continuously throughout their lives. Each tooth can grow to around 6cm in length providing Great White Sharks with a formidable bite when they are attacking their prey.

Great White Sharks are fearsome carnivores that primarily hunt large marine mammals in order to gain their nutrition. Seals, sea lions, porpoises, dolphins and smaller whales are among their most commonly hunted prey species around the world. Great White Sharks have poor eyesight in comparison to their other senses and use both their sense of smell and ability to detect vibrations caused by animals in the water to detect their prey. Once located, Great White Sharks fiercely attack with great speed and force before retreating and leaving their wounded prey to weaken before returning to feed once it is safe to do so. Although they are largely solitary, Great White Sharks can be seen in pairs or small groups to feed on a large whale carcass. In these circumstances, larger and more dominant individuals feed first with varying swimming display patterns thought to contribute to establishing their dominance hierarchy.

Credit : a-z animals

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Sharks do not have a swim bladder. Instead, they have a large liver filled with oil. Because oil is less dense than water, all of this oil helps sharks float in the ocean.

Sharks have livers different from other animals. It takes up much more internal space and serves more functions than simply helping with digestion; the oil inside the liver helps sharks stay buoyant under water.

While digestion is an important function of a shark's liver, it's not the reason the liver is so big or why it's filled with oil. The oil, called squalene, is lighter than the water. A shark's body is naturally heavier than water, and he doesn't have a swim bladder to fill with air like some other fish. The oil lightens the shark's body, providing buoyancy so he won't sink. Sharks must keep swimming to push water past their gills to breathe, and buoyancy is key to keeping on the go and staying off the ocean floor. Sharks use their pectoral fins to help them change directions in the water, but without the oil, sharks would expend too much energy swimming and staying buoyant than they could replace with their food.

Credit : Pets on Mom

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Up to two thirds of the total weight of a shark's brain is dedicated to smell.

They’re super-sensitive to smells that are important to their survival. Including scents produced by potential predators, prey or a mate.

Some sharks can detect the blood of prey from a huge distance - one part of blood to one million parts of water. That's equal to one teaspoon in an average sized swimming pool.

Light doesn’t travel well through water. So sharks need to maximise the amount available to help them see. With eyes positioned on the side of their head they're able to see in almost all directions. But, their vision becomes more acute 15m from an object. It's not until this point that sight becomes their dominant sense.

Like cats, sharks also have a ‘tapetum lucidum’. A reflective layer of shiny cells that lies behind the retina. This improves vision in low light conditions, allowing nocturnal and deep-water species to hunt effectively. It also gives their eyes a green glow in the dark.

Sharks have an acute sense of hearing and are sensitive to low-frequency signals. They're able to track sounds and are particularly attracted to sounds made by wounded prey.

Their ears are located on either side of their head, behind the eyes. From the outside these are visible as 2 small holes. These are made up of 3 cartilage tubes filled with fluid and lined with hair cells. Sound waves cause these tiny hairs to vibrate and the brain then interprets the sound.

Credit : Shark Trust

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Worldwide there are probably 70-100 shark attacks annually resulting in about 5 deaths. We say “probably” because not all shark attacks are reported; our information from Third World countries is especially poor, and in other areas efforts are sometimes made to keep attack quiet for fear of bad publicity.

While the term "shark attack” is in common use for instances of humans being wounded by sharks, it has been suggested that this is based largely on the assumption that large predatory sharks (such as great white, bull, and tiger sharks) only seek out humans as prey. A 2013 review recommends instances where a shark clearly predates on a human should the bite incident be termed an "attack, " implying predation. Otherwise, it is more accurate to class bite incidents as "fatal bite incidents". Sightings do include physical interaction, encounters including physical interaction with harm, shark bites include major shark bite incidents, including those that require medical attention, and fatal shark bite incidents result in death. The study suggests that only in a case where an expert validates the predatory intent of a shark would it be appropriate to term a bite incident an attack.

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The skin of the shark is unique in many ways. It is characterised by its grey colour and the contrast between its slippery appearance and its rough tactile texture.

These teeth are what makes the shark feel rough and what has led to the use of shark skin as sandpaper. The skin is so rough, in fact, that softer animals brushing against it can be badly injured. These denticles’ spines point towards the tail, so the rough effect is best felt by moving one’s hand over the body from the tail to the head.

They are arranged in a mosaic pattern which surrounds the body of the shark like a helix. This acts as a supportive corset. Because the sharks have no skeletal bones, the muscles used for swimming are attached directly to the inside of this corset. This saves energy, allowing them to swim faster and further without tiring.

Shark skin is usually grey in colour, with the top of the body being darker than the underneath. This means that the shark’s body camouflages with the dark depths of the ocean when viewed from above as well as the lighter surface of the water when viewed from below.

Credit : Sharks info

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As you might suspect, the number of teeth a shark has depends upon exactly what type of shark it is. There are many, many different types of sharks in the world's oceans, and the number of teeth they have can vary greatly.

For example, great white sharks have approximately 50 teeth at any one time (their “working" teeth). Like most sharks, however, they have multiple rows of teeth in development that are ready to take the place of teeth that fall out. Some sharks have over 300 teeth in various stages of development within their mouths at any one time!

Unlike human teeth, shark teeth are not very strong and tend to fall out easily. It's not a big deal for sharks, because they are constantly producing new teeth to replace the ones they lose. In fact, some sharks can have over 50,000 teeth over the course of their lives!

Many sharks have teeth in layered rows. Both their upper and lower jaws can have 2-3 or as many as 15 such rows. Their teeth do not have roots, so they break off easily and may last as little as a week. New teeth can move forward to replace lost teeth within a day to a couple of weeks. The skin within a shark's mouth moves new teeth into position like a conveyor belt.

Although it might sound like a bad thing to be constantly losing teeth all the time, this system works well for sharks. Over history, sharks have developed extremely strong jaws that give them the powerful bite that makes them the apex predators of the oceans.

Credit : Wonderopolis

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White shark teeth in that they are larger and thicker, the serrations on each tooth occur in regular intervals, and they possess a bourlette (a darker, chevron-shaped region near the tooth’s root). The largest extant megalodon tooth measures 17.8 cm (6.9 inches) in length, almost three times longer than those of modern white sharks (which are typically about 5.4 cm [2.1 inches] long). In addition, megalodon possessed a ferocious bite; its bite diameter was 3 metres (about 9.8 feet), several times larger than the bite diameter of averaged-sized white sharks.

Great white sharks bear live young and females give birth to between two and 10 pups per litter, and perhaps as many as 14. Researchers think the gestation period is anywhere from 12-22 months which would only allow for breeding to occur approximately every other year.

Male great white sharks generally arrive at the same time to the Farallon Islands off  the California Coast and the offshore Island of Guadalupe, Mexico from late July through August, and females arrive to these locations several weeks thereafter. These sharks are observed at their coastal aggregation sites through February.

Great white sharks are opportunistic predators, feeding from the ocean’s surface to the seafloor. As great white sharks grow in size, so does the range of their prey. Smaller great whites prey on fish, rays, and crustaceans and when they are larger also eat seals, sea lions, dolphins, seabirds, marine turtles, rays, and other sharks.

Credit : Oceana USA

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