And you, did you have fear in your childhood, when going into sea that somewhere near might swim a shark? :) I had. My post, however, is not imbued with a goal to dispel it, but it will show how things are in reality.

Relatively recently, I have felt a desire to study the underwater world, and I even enrolled in several courses that were to begin in a few weeks. And now I have a great opportunity to find out myself, and share with you a lot of interesting things about the topic below.

I chose the course of «Sharks! Global Viodiversity, Biology and Conservation», which was created by two authoritative establishments — Cornell University and the University of Queensland.

HABITATS

Sharks live practically in all corners of the world, but there are special species that live only in a certain area. Even if the environmental conditions allow to live there for a certain type of sharks, this does not mean that they are necessarily found there. Because there is one factor that influences this situation — presence of food or vice versa, its absence, when sharks migrate elsewhere.

Screenshot from the course video

Although the maps show an approximate territory where sharks can be found, they do not reflect the movement trajectory of individual animals. So, for example, an individual of a salmon shark crossed the distance from Alaska to California and back, i.e. the shark returned back to its place, but swam a lot of kilometers during migration.

Today, technology has already reached the point where anyone can monitor movement of sharks online due to the fact that special sensors are attached to the sharks. Earlier, about 30 years ago, the tracking technology worked quite primitively — a mark was drawn on a shark, with its help there was determined its movement to another point, when fishermen caught it somewhere in many kilometers away.
Modern technologies, however, allow not only to track, but also to record depth and temperature of water in which an animal is located, as well as the amount of light that gets into it. Accordingly, scientists collect information not only about the coordinates, but also about the environment in which the shark is situated. There is a group of sharks that swim to the middle of the Atlantic Ocean, where they dive to 1000 meters.

Imagine that sharks with sensors have their own «followers" and their amount is already over 80,000! Shark sensors are connected to a satellite, and when the shark is on surface, it gives signals that immediately display its location on Twitter. One of these sites is here Unfortunately, the system does not work perfectly and sometimes technical errors happen: the sensor can not be compared with GPS, so position inaccuracies are possible, and sometimes the sensor itself stops working.

CONDITIONS OF HABITATION

The main variable in the ocean is its depth, somewhere it is great, somewhere not. In deeper waters, the temperature is much lower than on the surface, primarily because light penetrates into the water to a certain depth. For example, the sun's rays penetrate the water to a maximum of 200 m. This zone is also called a photic zone. It is a productive area of ​​the ocean, because here a process of synthesis occurs.

After the photic there is a mesopelagic zone (200-900 m), which is also called twilight area due to the fact that the light no longer reaches here and creates a twilight visibility.

Next is the bathypelagic zone (900-3700 m) — the zone of ocean depths. It is home to many sharks.

Even deeper there is the abyssopelagic zone at a distance of more than 4000 m from the surface. Here you can also find sharks, but to a lesser extent.

WATER GEOGRAPHY

The territory from the shore and to a certain point is called the continental shelf, then there is a marginal sea, followed by a deep ocean trench adjacent to the abyssal plain. In the middle of the ocean basin there is a ridge that is critical for existence of certain species of sharks. Also it is worth remembering the underwater mounts around which animals often gather. Further, the plain becomes a continental slope followed by the continental shelf on the other side of the ocean basin.

GREAT BARRIER REEF

There are zones where different kinds of flora and fauna are concentrated, and the smaller their territory, the more they are protected and conserved. For example, reefs are one of the most popular biodiversity on Earth.

The main condition for the habitat of sharks in a certain locality is presence of plankton, because the food chain of organisms begins first of all with it.

Great barrier reef is located in Astralia and is characterized by more than 2900 separate reefs. Especially a great variety of sharks can be found in the waters around Heron island.

In Heron one can observe sharks from the dock, and also there is a built "underwater room" with glass partitions, from which you can enjoy marine life from the inside. Tiger sharks are rare guests, outside the harbor there are silk and silver sharks. If you are lucky, you can observe how the hammerhead shark searches for its most favorite food of a stingray in the coastal area.

CHONDRICHTHYES

Although the name of the course is «Sharks», one can not but consider «their cartilaginous relatives» — chimaeras and rays. This group of fish appeared more than 500 million years ago and today there are about 1200 of their species. They all have jaws, teeth, fins and a cartilaginous skeleton, but they are characterized by different forms and features of nutrition, movement and reproduction.

Fins

With what to begin? Perhaps, with the fins. The picture below shows a Squalus achantias shark: its fins are located in the middle of the body (dorsal and caudal), as well as chest and pelvic fins on the sides. They are like the analogues of human hands and feet in the course of evolution.

It is interesting that the end of the spine is wrapped in the upper part of the caudal fin.

Sharks have mouths, spiracles (located behind the eyes of fish, drawing water to get oxygen) and gill slits.

Picture

Anatomy

If you compare sharks and mammals, the first thought is that the skeleton of these animals is very different from each other. The answer is yes and no at the same time.

The body of sharks consists of 10 systems of organs and they are: the integumentary system, the skeletal system, the muscular system, the nervous system, the endocrine system, the digestive system, the respiratory system, circulatory system, excretory system and reproductive system.

For now that is all. To be continued!

All pictures are under License CC0.