What Is A Shark
Table of Contents
Sharks are certainly among the most diverse and most populous groups of aquatic creatures. They are varied in terms of size, diet, temperament, growth rate, even in terms of habitat choice, so it is probably easier to list features that are specific for each shark species than to find common traits, but there are some traits that all of them share.
Sharks are so called apex predators – top predators at the top of the aquatic food chain, with an important role in regulating the populations of the species that are below them – that inhabit all the seas and oceans of the world and live in some of the world’s rivers and estuaries, too.
All sharks share a number of physical features:
All sharks have skeletons made of cartilage, a tissue that is not as rigid and heavy as bones and allows sharks to move more freely and be more resilient;
All sharks breathe through gills;
They all use a process called osmoregulation to keep the amount of salt in their body at certain levels and to prevent the fluids in their body from becoming too diluted or too dense. They use their gills to achieve this balance.
They all have multiple rows of teeth – teeth that they lose and re-grow regularly;
All sharks have very good eyesight and their sense of smell is also excellent;
These features are more related to anatomy and not so much to size, shape, habitat or behavior – the 500 different shark species known today vary so largely in terms of physical appearance and habits that they need a more complex classification system.
There are numerous features that make sharks truly special and peculiar – here are just a few:
A shark’s denticles – which are tooth-shaped scales – make it possible for it to swim fast through the water without collecting algae deposits and barnacles, making them almost completely free of parasites;
Sharks have their own built-in toothpaste – the exterior of sharks’ teeth is made of fluoride, a substance frequently used in toothpaste;
Sharks tan too – some hammerheads are known to swim near the surface of the water to get tanned because darker skin means better camouflage.
Sharks first evolved about 450 million years ago, but they kept developing for another 140 million years, until their body design became as we know it today. The oldest evidence about the existence of sharks dates back to before vertebrates developed and, according to paleontologists, the ancient shark looked very different from what sharks look like today: it was only about 1 meter long, it had inflexible, triangular fins, slim jaws and teeth that had pointed ends. There is evidence that sharks lived in freshwater initially – it was only about 220 million years ago that they took to the sea and conquered it. Modern sharks date back to only about 100 million years, the white shark being one of the oldest species living today.
What Is A Shark?
Dive into the depths of the ocean, and you’ll find one of the most formidable predators that has fascinated humans for centuries: the shark. These creatures, belonging to the group Elasmobranchii, which also includes rays and skates, have roamed the Earth’s oceans for over 400 million years. With over 500 species ranging from the tiny dwarf lanternshark to the colossal whale shark, sharks boast an incredible diversity. They are not just ruthless hunters as often portrayed; sharks play a crucial role in maintaining the balance of marine ecosystems. Their anatomy, behavior, and survival strategies make them one of the most intriguing subjects in marine biology and beyond.
Anatomy and Physiology of Sharks
Understanding Shark Skeletal Structure
Sharks are known for their cartilaginous skeletons, which are much lighter and more flexible than bone. This unique feature, composed of a tough material called chondroitin, allows for the agility and speed sharks are famed for. Unlike bony fish, sharks’ skeletons do not calcify, enabling them to grow larger and heal faster from injuries. Their skin, covered in dermal denticles, reduces friction as they glide through water, contributing to their efficiency as apex predators.
The Remarkable Sensory Systems of Sharks
Sharks possess an array of sophisticated sensory organs that make them excellent hunters. The lateral line system, a network of fluid-filled canals on their bodies, detects vibrations and movements in the water, alerting them to potential prey. Additionally, sharks have ampullae of Lorenzini, electroreceptor organs that allow them to sense the electric fields generated by the muscle movements of other organisms. Their keen sense of smell, capable of detecting a single drop of blood in millions of drops of water, is also noteworthy.
Shark Behavior and Diet
Predatory Tactics and Feeding Habits
Sharks are known for their diverse feeding strategies. Species like the great white shark (Carcharodon carcharias) use their powerful jaws and sharp teeth to prey on large mammals and fish. Others, like the basking shark (Cetorhinus maximus), are filter feeders that consume plankton. Their hunting techniques can be highly specialized; for example, the thresher shark uses its long tail to stun fish before consuming them.
Social Behavior and Migration Patterns
Contrary to popular belief, not all sharks are solitary hunters. Some species, like the scalloped hammerhead (Sphyrna lewini), form large schools during migration. Sharks’ migration patterns are often linked to breeding or feeding grounds and can cover thousands of miles. Understanding these patterns is crucial for studying shark behavior and ensuring their protection.
Shark Habitats and Adaptations
The Diverse Ecosystems Sharks Inhabit
Sharks are found in all of the world’s oceans, from shallow coastal waters to the deep sea. Each species has adapted to thrive in a specific habitat. For instance, the Greenland shark (Somniosus microcephalus) lives in cold Arctic waters, while the tiger shark (Galeocerdo cuvier) prefers warm, tropical seas. Their ability to adapt to a wide range of environments is a testament to their evolutionary success.
Evolutionary Adaptations for Survival
Over millions of years, sharks have evolved various adaptations that have ensured their survival. Their reproductive strategies, for example, vary greatly among species, from laying eggs (oviparous) to live birth (viviparous). Some species, like the hammerhead, have uniquely shaped heads that improve their ability to find prey. These adaptations highlight the evolutionary prowess of sharks in the marine world.
In conclusion, sharks are far more than the menacing predators often depicted in media. They are complex, fascinating creatures that play a vital role in marine ecosystems. Their diverse species, intricate anatomy, and sophisticated behaviors make them a subject of endless interest and importance in marine biology and conservation.
FAQs about Sharks
What is the largest species of shark?
The largest shark species is the whale shark (Rhincodon typus), which can grow up to 60 feet in length. Despite their size, whale sharks are gentle giants, feeding primarily on plankton through filter feeding.
How do sharks reproduce?
Shark reproduction varies by species. Some sharks lay eggs in protective cases, known as oviparity, while others give birth to live young, referred to as viviparity. There are also species that have a combination of these methods, known as ovoviviparity, where eggs hatch inside the female, and the young are born live.
Can sharks really smell a drop of blood from miles away?
While sharks have an extremely acute sense of smell, the idea that they can detect a single drop of blood from miles away is an exaggeration. They can detect small amounts of blood in water, but this ability is more localized and not as far-reaching as popularly depicted.
Why do sharks attack humans?
Shark attacks on humans are extremely rare and often a case of mistaken identity. Sharks might confuse humans with their usual prey, like seals, especially in murky waters or low visibility conditions. Most sharks are not aggressive towards humans unless provoked.
Are all sharks dangerous to humans?
No, not all sharks are dangerous to humans. Out of over 500 species of sharks, only a handful are involved in incidents with humans. The majority of sharks pose no threat to humans and avoid contact whenever possible.
