Coming from the cartilaginous fish family, sharks, or selachimorphs, are present in the waters of the planet’s oceans, as well as in certain large rivers and lakes.
The particularities of the shark
These enormous fish have been around for 420 million years. The best known, the megalodon, became extinct 1.6 million years ago. It reigned in tropical waters with its 20 m length.
Over time, sharks have adapted their shape to survive. Apart from river sharks and bull sharks which can also live in fresh waters, it is only found in the saline waters of the oceans, up to 2,500 m deep. The smallest shark measures 20 cm (Etmopterus perryi) and the largest reaches 20 m (the whale shark).
The shark is a predator with the exception of the whale shark which only feeds on plankton. It has several rows of teeth which are renewed during its life. Its skin is naturally protected from parasites and improves its hydrodynamics.
The different families of sharks
Today there are more than 500 species of sharks which can be divided into 35 families. Rays are exempt from this classification, although they are considered selachimorphs. Sharks are grouped into two superorders, themselves comprising 4 orders.
The superorder Galeomorphi
In this family of sharks, there are 4 orders:
the Carcharhiniformes composed of 270 species, such as hammerhead sharks, dogfish sharks, etc.); Heterodontiformes grouping together primitive sharks, such as sleeper sharks, etc. ; the Lamniformes which include the best known sharks as well as the rarest, such as great white sharks, basking sharks, largemouth sharks, etc. ; Orectolobiformes including specimens from tropical coastal waters such as nurse sharks, whale sharks, etc. The superorder Squalomorphi
Like the first superorder, it is also divided into 4 orders, namely:
the Hexanchiformes which bring together the 6 most primitive forms, such as the sandfish, the lizard shark, etc. ; the Pristiophoriformes only with the saw shark; the Squaliformes, the best known of which is the Dogfish; the Squatiniformes with the angel shark and 12 other species of angel sharks.
Only 5 categories of sharks are dangerous for humans because of their size and their diet:
tiger sharks; great white sharks; bull sharks; mako sharks; Longimane sharks.
Shark attacks are very rarely intentional, because they confuse humans with their prey. Between 2001 and 2010 in the USA, 10 deaths were caused by sharks, compared to 263 by dogs.
Sharks threatened with extinction
A third of shark species are today threatened with extinction due to overfishing, but also poaching and other causes linked to human activity. In addition to being consumed, humans use the shark for leather goods, cosmetics, but also for tourism. To compensate for this disappearance, certain territorial waters are now classified as “squala sanctuaries”.