https://www.linkedin.com/in/sharvari-palve-14a021233/Nature Of Selachimorpha
About Shark
Alt: One of the rear species of shark;
Image Description: Shark is an animal.
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Sharks are one amongst the groups of Elasmobranch fish characterized by a cartilaginous skeleton, five to seven-gill slits on the sides of the head and pectoral fins that are not fused to the top. In today’s time, these are classified within the clade Selachimorpha and are the sister group to the rays.
The term shark has also been incorrectly accustomed check with the extinct members of the Elasmobranchii, which are technically outside the Selachimorpha clade. To be clear within the broader information, the earliest known sharks originate from quite 420 million years ago.
There’s a stimulating thing about sharks’ covering of dermal denticles that protects their skin from damage and parasites additionally improving their fluid dynamics. they have to induce numerous sets of replaceable teeth.
EVOLUTIONARY HISTORY
It’s still evident in several species termed “Dogfish” or the “Porbeagle”. Now there’s a disproven theory that derives from the Yucatec Maya sense “SHARK”.
Fossil Record:- Existence of shark-like chondrichthyans have evidence that dates from the Ordovician, 450-420 million years ago. This was basically before the land vertebrates existed and before a spread of plants had colonized the continents. Cladoselache is among the foremost ancient and primitive shark-like fish which was about 370 million years ago, found within Paleozoic strata in Ohio.
Taxonomy:- the current molecular studies support the monophyly of both groups of Sharks and Batoids. Galea and Squalea are the two subdivisions of the superorder Selachimorpha. The Galea consists of Heterodontiformes, Orectolobiformes, Lamniformes and Carcharhiniformes.
LIFE HISTORY
Alt: Historical view of species;
Image Description: lifespan varies with species.
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Generally shark’s lifespan varies by species. Among these, whale sharks may additionally relive 100 years. variety of the earlier estimated study suggested that the Greenland Shark could reach about 200 years but a recent study found that a 5.02-meter long specimen was 392 years old making it the longest-lived vertebrate known.
Reproduction:- These are K-selected reproducers meaning that they produce a touch number of well-developed young. Compared to many other fishes, sharks mature slowly. Lemon Sharks reach sexual maturity at the age of 13-15 years.
Sexual:- These are execute internal fertilization. Mating isn’t seen in sharks. In many of the larger species, females have bite marks that appear to be a result of a male grasping them to require care of their position during mating. These bite marks in females may additionally come from courtship behavior that the male may bite the female to suggest his interest.
Asexual:- many documented cases show, that a female sharks who has not been connected with a male has conceived a pup on her own through parthenogenesis. in step with scientists reproduction within the wild is rare and possibly a last-ditch effort to breed when a mate isn’t present.
MENACING
In 2008 a scientific survey estimated that nearly 100 million sharks were being killed by people once a year, because of commercial and recreational fishing. And currently, in 2021 it’s now estimated that the population of oceanic sharks and rays had dropped approximately 71% over the previous half-century.
For the requirement of shark fin soup, sharks are often killed. All the fishermen capture live sharks, fin them and dump the finless animal back into the water. This shark finning involves removing the fin with a hot metal blade. And this winds up within the immobile shark which soon dies from suffocation or predators.
In Asian countries, Shark fin soup could also be a standing symbol and is erroneously considered healthy and stuffed with nutrients. Sharks are also being killed for meat purposes. Majorly European countries practice such a cuisine format. In general, sharks reach sexual maturity only after some years and produce few offspring as compared to other harvested fish. Before they reproduce, harvesting sharks severely impacts future populations
PERORATION OF SHARKS
Alt: Human relation with sharks;
Image Description: How can we preserve the rest species.
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Talking about sharks, it is a usual combination of biological characteristics like slow growth, delayed maturation, long reproductive cycles, low frequency, and long life. These all factors make sharks extremely susceptible to overfishing. Shark species on specific data are scarce and difficult to induce. There are concerns about the overfishing and collapse of shark stocks that have endangered worldwide attempts to manage and conserve sharks.
Top 10 Facts About Sharks
1. THERE ARE OVER 500 SPECIES OF SHARK
143 of these are under threat, listed by IUCN from vulnerable to critically endangered.
2. SHARKS ARE APEX PREDATORS
Many have several rows of teeth and can lose and replace thousands of teeth in their lifetimes. As predators, sharks play a vital role in the health of marine ecosystems – by eating fish they help create balance in the food chain.
3. THEY CAN VARY DRAMATICALLY IN SIZE
From the smallest dwarf lantern shark (which is about the size of a human hand), to the largest which can be up to 12 metres long – the whale shark.
4. SHARKS LIVE IN MOST OCEAN HABITATS
They can be found in beautiful, tropical coral reefs, to the deep sea, and even under the Arctic sea ice.
5. THEY CAN BE WEIRD AND WONDERFUL
Goblin sharks can be a bright pink colour, and hammerhead sharks have hammer-shaped heads (duh!), which they’ve been known to use to pin stingrays against the sea floor!
There’s even a cookie cutter shark, which are named for the round ‘cookie’ bite marks they leave.
6. MOST SHARKS ARE COLD-BLOODED
For most sharks, their body temperature is cold, like the temperature of the water they swim in.
But unlike most sharks, great white sharks are partially warm-blooded, allowing them to move faster when hunting prey.
7. WE GET SHARKS AROUND THE UK
From basking sharks to blue sharks and even Greenland sharks.
The basking shark is Britain’s largest fish (and the second largest in the world). It can grow up to 11 metres long and weigh up to 7 tonnes – about the size and weight of a double-decker bus.
8. SHARKS HAVE A SIXTH SENSE
All sharks have a ‘sixth sense’ that helps them hone in on prey during the final phase of attack: the ‘amupllae of lorenzini’ are found on sharks’ snouts and can sense the electric fields emitted by animals in the surrounding water.
9. THEY’VE BEEN AROUND FOR A LONG TIME
Sharks have been around for over 400 million years – long before dinosaurs. Because their skeletons are made of cartilage (like our noses) instead of bones, they don’t leave fossils like other animals – but fossilised shark teeth have been found.
10. THEY’RE UNDER THREAT
Many sharks are accidentally caught in fishing gear, as well as caught deliberately for their fins, which are a delicacy in Asia.
Their ocean home is also in danger. From climate change warming the water – affecting both habitats, prey and shark population shifts – to plastic pollution, which could cause entanglement or be ingested, especially by filter feeders.
Reproduction
About 70% of all known shark species give birth to live young, with the gestation period lasting from 6 to 22 months.
Pups are born with a full set of teeth, and are capable of taking care of themselves. Once born, they quickly swim away from their mothers, who sometimes feed on the pups. Litters vary from one or two pups (great white shark) to one hundred pups (blue shark and whale shark).
Some sharks are oviparous, laying their eggs in the water. Shark eggs (sometimes called “mermaid’s purses”) are covered by a tough, leathery membrane.
Most sharks are ovoviviparous, meaning the eggs hatch inside the female’s body, with the babies developing within the mother, but there is no placenta to nourish the pups. Instead the young feed on the egg’s yolk.
The pups eat any unfertilized eggs and sometimes each other. Very few pups in a litter survive until birth due to this form of sibling cannibalism. Great white sharks, mako sharks, nurse sharks, tiger sharks, and sand tiger sharks give birth this way.
Some sharks are viviparous, meaning that the females give live birth: the eggs hatch inside the female’s body, and the babies are fed by a placenta. The placenta helps transfer nutrients and oxygen from the mother’s bloodstream and transfers waste products from the baby to the mother for elimination.
Examples of viviparous sharks include the bull sharks, the whitetip reef sharks, the lemon sharks, the blue sharks, the silvertip sharks, and the hammerhead sharks. Although long thought to be oviparous, whale sharks are viviparous, and pregnant females have been found containing hundreds of pups.
Factors affecting shark populations
In a world where the mighty shark’s reign is threatened, the degradation of their underwater kingdom poses an imminent danger. Human endeavors, like coastal expansion and pollution, wreak havoc on the coral realms and coastal domains these magnificent predators depend on.
As if this wasn’t enough, humanity’s insatiable hunger leaves no room for the ocean’s natural balance to prevail – destructive fishing practices ravage the sea, leaving prey scarce and our finned protagonists struggling for survival. Compounded by the sharks’ slow growth and scarcity of offspring, their dwindling numbers beg the question: can these underwater titans withstand the onslaught brought upon them by the Earth’s terrestrial rulers?
The answer, though uncertain, lies in our collective ability to coexist harmoniously with sharks. We must take action and safeguard the future of these ancient predators. This starts with mitigating the damage wrought by human activity, like protecting habitats and curbing overfishing. It is also important to pass laws that protect sharks from exploitation and pass on a legacy of conservation for generations to come.
If we act now, we can ensure that our oceans remain rich with sharks – untamed, majestic creatures worthy of awe and admiration. Together, we can shape a brighter tomorrow for one of Earth’s most mysterious icons – the shark.
Sharks are some of the most mysterious and awe-inspiring creatures on our planet, but they are facing many threats. In order to protect these important predators, we must first gain a better understanding of their population size and distribution.
Estimating the number of shark species is an extremely difficult endeavor, but with the combination of scientific observation, direct sampling, genetic analysis, and computer modeling, researchers can gain valuable insights into shark populations across the globe. With this knowledge, we can create better conservation strategies and ensure their survival for generations to come.
Estimating the global shark population
Estimating the global shark population is an incredibly challenging task, and it is believed that there are approximately 100 million sharks in the world. Scientists have implemented various techniques to estimate their numbers, including tagging and tracking studies, genetic analysis, and fisheries data.
Tagging and tracking studies involve capturing and fitting sharks with tags that record their movements and behaviors, which enables researchers to estimate populations in different regions. Genetic analysis involves taking small samples of tissue or scales from sharks and analyzing their DNA to determine population size and structure.
Additionally, fisheries data can be used to estimate population trends in areas where fishing is common. By combining these methods, scientists can gain a better understanding of the global shark population and develop strategies to protect them.
HOW MANY SHARKS ARE ENDANGERED?
The most recent global assessment of the Class Chondrichthyes – otherwise known as the cartilaginous fishes, the group of animals to which sharks belong – showed that more than one-third of sharks, rays and chimaeras are threatened with extinction. Of the 1,199 species assessed, 121 are classed as Endangered, 90 as Critically Endangered and 180 as Vulnerable, according to criteria established by the International Union for the Conservation of Nature (IUCN). Looking at sharks specifically, 31.2% of all species assessed are threatened with extinction. And given the rate at which some species are declining, scientists expect that figure to grow in the coming years.
What is the biggest threat to sharks?
The shark finning industry is, without a doubt, one of the biggest threats facing the world’s shark populations right now. But it is far from the only threat. The shark liver oil industry is also responsible for driving up demand for shark fishing, and so is the shark meat market. Just like a shark fin, shark meat is considered a delicacy in a number of countries, including India, Japan, and Iceland, where fermented shark (called kæstur hákarl) is a national dish.
All of this contributes to overfishing, which is the biggest threat facing sharks right now. And the consequences are serious: in the past five decades, shark populations have declined by 70 percent, notes Greenpeace. “When it comes to solving the problem of overfishing sharks, every country has got a role to play,” the environmental nonprofit says. “No single country, nor cuisine, can be blamed for the staggering number of sharks being killed every single year–but every country can step up to solve this problem.”
Strict rules and legislation around the import and trade of shark products need to be implemented, notes Greenpeace. And for the sharks that are left, we must protect them by creating a “network of ocean sanctuaries across the world,” it adds.
It’s important to note that it’s not just the industries specifically targeting sharks that are blamed for their decline. Millions of these marine predators also end up as accidental bycatch, fatally caught in fishing nets meant for other fish. But whether they become soup, meat, oil, or accidentally caught in a net, sharks are suffering. And that’s not just an ethical crisis, but also an environmental one, too.
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Why are sharks key to a healthy ocean?
Sharks are apex predators, which is also known as the “top” predator. This means that they are at the very top of the food chain, apart from humans, they’re not actively hunted by any other animals around them. And because of this, they play a very important role in maintaining underwater ecosystems—they help to control prey numbers, which in turn, regulates the amount of smaller predators in the ocean.
“The removal of an apex predator can have knock-on effects on the entire ecosystem, including the landscape,” science writer and animal behavior researcher Leoma Williams notes for BBC Wildlife.
“For example, when grey wolves were hunted to extirpation in Yellowstone National Park the population of elk, their primary prey soared,” she continues. “This in turn led to the overgrazing of woody trees such as aspen and willow. Beavers declined as a consequence of this, as they depend on willow to survive the winter.”
The same thing is happening in the ocean, except it’s not grey wolves, it’s sharks, and instead of elk, it’s fish-like groupers. The groupers eat the smaller fish, the ones that help to manage microalgae and coral, and the entire ecosystem, and the health of coral reefs (which are vital in tackling the climate crisis), becomes under threat.
But there are efforts underway attempting to counteract the impact of shark overfishing. One initiative, called ReShark, is defined as an “international, collective effort to recover threatened sharks and rays around the world.”
Right now, it’s raising 500 endangered baby zebra sharks, all of which were born in captivity. In time, it will release them back into the wild in an attempt to combat the detrimental impacts of habit degradation and the shark finning trade. After that, the sharks will be monitored to see if the population recovers, but the group also aims to educate local communities about why sharks are so ecologically important.
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Sharvari Palve
31-03-2022
