Did You Know?
The bilobed liver of the basking shark extends through the entire abdominal cavity, and it is believed that the oils stored in the organ is used as an energy reserve. The oils in the liver is linked to buoyancy regulation too.
Basking sharks (Cetorhinus maximus) are slow-moving sharks that belong to the family Cetorhinidae and the genus Cetorhinus. In fact, it is the only species of this family and is the second largest fish in the world, after the whale shark (blue whale is much bigger than whale shark and is the largest mammal in the world). The name basking shark is derived from their habit of frequenting the warmer water on the surface, as if they're basking in the sun.
❥Basking Shark Identification Features
Basking sharks can grow to a maximum length of 30 to 33 feet and a body weight of around six tons. An average adult can have a body weight of around five tons and a length of 20 to 25 feet. It has been observed that female basking sharks are bigger in size, as compared to the males.
➽Color Of Basking Sharks
Basking sharks have a grayish-brown to bluish body color, with some of them having paler shades on the ventral side. The body color may slightly vary between individuals. Even though, they have the typical body shape of sharks, basking sharks can be distinguished with their unique features.
➽Basking Sharks Have a Conical Bulbous Snout
Basking sharks have a conical, pointed, and bulbous snout, which may have a hooked appearance in juveniles. The hook-like snout is said to be useful for feeding inside the womb. The elongated, hook-like snout may have a sharp tip that may point upwards or downwards. The shape of the snout transforms, as they turn adults and grow to a length of around 13 to 16 feet.
➽Large Mouth with Rows of Tiny Teeth
Basking sharks have a large, wide mouth that is an adaptation for their feeding behavior. An adult basking shark can open its mouth to a width of around one meter. They have very small, hooked teeth, arranged in rows. It is said that each row consists of around one hundred small teeth. The lower jaw has six rows, and the upper one has nine. The size of the teeth is around 0.25 inches. It is said that basking sharks do not use their teeth for feeding.
➽Basking Sharks Have Extended Prominent Gill Slits
One of the distinguishing physical features of a basking shark is the long gill slits located on the sides of the head. There are five gill slits on each side and they extend from the top to the bottom. Though they are long and unusually extended, the gill slits do not encircle the head completely. These gills have thousands of bristle-like gill rakers, that help these sharks to filter food from water. These gill rakers are shed periodically.
➽Crescent-shaped Caudal Fin and Angular Dorsal Fin
They have very large and angular dorsal fin that may have a length of around two meters. Their pectoral fins (located on the ventral sides, after the gill slits) are also large, and are used for changing their position in water (like the wings of an airplane). The tail fin (caudal fin) is crescent-shaped. The triangular-shaped dorsal fin is often visible when they move close to water surface. Shark fins are poached and traded, for they have high international price.
➽Basking Sharks Have Large Liver
This is an interesting fact about basking sharks, that is, they have a large, bi-lobed liver that extends to the entire length of the abdominal cavity. It is said that the liver amounts to 25% of its body weight and could be linked to storage of energy. It is also believed that the liver has an important role in regulating buoyancy. It is in the liver that these sharks store fats in the form of oils. In adult basking sharks, the liver may weigh around a ton.
➽Well-developed Olfactory Lobes
The eyes are very small and are believed to be used for detecting change in light levels. They have a highly-developed sense of smell. It is said that the olfactory tract in the brain is longer than the length of the entire brain. Another interesting fact is that their brain is much smaller than the cavity in which it is located. The brain is attached to the walls of the brain cavity with strands of tissues. The skin is covered with placoid scales and the whole body has a mucus layer cover.
Basking sharks are found in cold to warm temperate waters, especially near the continental shelf. These sharks can be found in the coastlines of the Atlantic as well as the Pacific Oceans. They can be seen singly or in groups (of up to 100 members) near the surface of the water.
Basking sharks are mostly seen from the surface to a depth of around 3000 feet. However, these sharks are found to be migratory, as they move thousands of kilometers, during the winters. They are often seen in regions with a high plankton concentration. It has been observed that the habitat of basking sharks are mainly situated close to land, like bays and estuaries. These giant sharks are slow-moving, but, sometimes, they are found somersaulting in the water.
❥Basking Shark Behavior
➽Basking Sharks are Filter Feeders
This is one of the characteristic traits of basking sharks. They are often seen with their mouth wide open, gill slits erect, and moving slowly through the surface waters. They feed on zooplankton that are found in the water that moves into their mouth, while they move. As they swim, the mouth is kept open for at least thirty to sixty seconds at a time. Once closed, the water in the mouth is released through the gill slits. The gill rakers sieve the water to retain the food, which is swallowed by the shark. If the concentration of food in the water is very low, the shark may keep its mouth open for a few minutes (at a time), so as to collect enough food for swallowing. This is passive feeding, which is different from active or suction feeding that is seen in other filter feeders like megamouth shark. In case of suction feeding, movement is not necessary for water to enter the mouth. Water is sucked into the mouth and pumped out through the gills. It has been observed that basking sharks can filter around 1800 tons of water per hour.
➽Basking Sharks Relish on Zooplankton
Basking sharks are massive in size, but they feed on zooplanktons, which consists of tiny aquatic animals like small crustaceans, small fish, fish larvae and eggs. They also feed on shrimp found in the depths of the sea. So, it can be assumed that they search for food on surface waters as well as in deep sea. The concentration of plankton must be around one gram per cubic meter of water. If the concentration is less, then these sharks start searching for areas that are abundant in plankton.
➽Basking sharks are Ovoviviparous
Reproduction in basking sharks is still unknown. It is believed that these sharks become mature within the age of six to thirteen years. Mating and the period of gestation is not clear. The gestational period could be one to three years. Basking sharks are ovoviviparous, which means that the young ones hatch inside the body of the mother. They feed on the yolk sac and the unfertilized eggs. Fully-developed young ones are around 1.5 to two meters in length, at the time of birth.
The decline in the population of basking sharks is mainly due to human hunting. They have been hunted in large numbers for their fins and liver. These sharks are now classified as 'VULNERABLE', by the IUCN.