Shark: Habits, Diet and Other Facts

Shark is a popular name for a type of fish belonging to the group of chondrichthyans, i.e. those whose skeleton is predominantly made of cartilage. Sharks are well known mainly as large predators, but this characteristic cannot be applied to all representatives of this group of animals.

Characteristics

Sharks are animals that belong to the same group as rays and chimaeras, and because they are fish, they have some very striking characteristics of this group of animals. Here are some of the characteristics observed in sharks:

• Gill breathing: Like all fish, sharks are gill-breathing animals, meaning that they use these structures to ensure that oxygen is drawn from the water.
• Hydrodynamic body: Sharks have a body that aids their movement in the aquatic environment, helping them to break through water resistance.
• Placoid scales: these make sharks have a surface that resembles sandpaper. These scales ensure more efficient swimming and have a tooth-like structure.
• Swimming fins: These fins help sharks to move in the aquatic environment. Strong movements of the trunk and the tail fin ensure the animal's movement. The pectoral and pelvic fins assist in maneuvers, while the dorsal fins help stabilize the animal.
• Lack of swim bladder: Sharks lack a swim bladder, which is a structure related to buoyancy. To solve this issue, sharks rely on a large liver, which contributes about 25% of their body mass, full of fat. This causes the animal's density to decrease.
• Structures for capturing electrical fields: when animals contract their muscles, they cause electrical signals to be emitted. Sharks are able to capture these electric fields and are therefore able to locate prey even if it is hidden.
• Claspers: structures found in male sharks that function as organs responsible for depositing the gamete inside the female's body. Due to this characteristic, we say that shark fertilization is internal.
• Cloaca: sharks have a cloaca, meaning that they have a chamber where the reproductive, excretory and digestive systems flow into.
• They can be oviparous, ovoviviparous, or viviparous: there are sharks that are able to lay eggs (oviparous), sharks that retain eggs in their oviduct (ovoviviparous), and sharks that are able to ensure the development of their young in the uterus (viviparous).

What do sharks eat?

Many people know sharks as large predators that feed on large animals such as seals. Some sharks do exhibit this type of behavior, and this is the case with the white shark, a species that feeds on seals, fish, and even sea turtles.

It is worth pointing out, however, that not all sharks exhibit this behavior. This is the case, for example, with the whale shark, which is classified as a filter-feeder. This animal feeds mainly on plankton.

Species

As stated, sharks are not a single species. Several species can therefore be referred to as sharks. Below we will talk about some of the most notorious sharks found in the world.

• Great white shark (Carcharodon carcharias): occurs in a large part of the seas and oceans, and is observed, even if less frequently, even in Brazil. It can reach about six meters in length and live for about 70 years. It is a great predator of the seas and feeds on the most varied animals, including other fish, turtles, seals, and penguins. It is a hunted species for its fins, which are used to make soup.
• Whale Shark (Rhincodon typus): A species with a robust body and flattened head, this is the largest existing shark. Its coloring is black, with lighter spots all over the body. This species feeds by filtration, ingesting some small fish and plankton present in the water. For this species there are records of individuals that are 20 meters long and 35 tons.
• Hammerhead shark: species of the genus Sphyrna are called hammerhead sharks. A striking feature of this type of shark is the presence of a flattened head typical of the group. The head, despite appearing inefficient, helps these animals in the swimming process and in visualizing their prey. Hammerhead shark species vary in size. The species Sphyrna zygaena, for example, can reach five meters in length and weigh about 400 kg.

Curiosities about Sharks

Although they are sexually reproducing animals, a female hammerhead shark that reproduced alone, without the need for a male, has been reported in a zoo in the United States. This individual reproduced asexually by parthenogenesis.

Sharks can gestate with more than one pup, and in some cases one pup has been observed to be killed by another in the womb. When one pup devours the other while still inside the mother's body, we say that intrauterine cannibalism has occurred.

Shark attacks are rare worldwide. Research in the United States showed that between 2001 and 2013 more people died from dog attacks (364 deaths) than from shark attacks (11 deaths).

Sharks have a very keen sense of smell. Some sharks are able to respond to substances in concentrations less than one part per 10 billion.

The white shark, when feeding on mammals such as seals, kills these animals by bleeding. In these situations, what is observed is that the shark holds the seal with its jaw until the prey stops bleeding, then it removes large chunks of the animal. In the case of sea lions, which are stronger prey, the sharks hold and release the animal several times until it bleeds to death.

The white shark is the best known and also the most feared shark. One of the reasons for the "bad name" of the white shark is the movie Jaws, directed by Steven Spielberg and released in 1975. The film, which shows a great white shark attacking tourists on a beach, was a great success, winning Academy Awards for Best Original Soundtrack, Best Sound Mixing, and Best Editing.