Basking Shark

Basking sharks are the second largest shark in the world, after the whale shark, which also makes them the second largest fish on Earth. They are the only surviving member of the Cetorhinidae family.

They were first described by Norwegian Bishop and Botanist Johan Ernst Gunnerus as ‘Cetorhinus maximus‘ from a specimen found in Norway. Their genus name ‘Cetorhinus‘ comes from the Greek words ‘ketos’ meaning ‘marine monster’ or ‘whale’ and ‘rhinos’ meaning ‘nose.’ Their species name ‘maximus’ is a Latin word which means ‘greatest.’

Along with whale sharks and megamouth sharks, basking sharks are one of the three plankton-eating sharks that are often seen close to the water surface, basking under the sun, which earned them the name ‘basking sharks’.

These giant sharks are cosmopolitan migratory species living in temperate oceans. Despite their huge size and intimidating appearance, these sharks are passive and harmless.

Description

Length: 312 in (792 cm). The largest recorded specimen is 40.3 feet (12.27 m)

Weight: 10000 lbs (5000 kg)

Body and Coloration: Basking sharks are greyish brown, darker on the top, and lighter underneath. They have a spotted body with a large, triangular, black dorsal fin on the back. The inner part of their mouth is white.

They have a lamniform body plan that is common in all other sharks. What differentiates the basking shark from great white sharks is their cavernous jaw and gill slits, which contain well-developed gill rakers. They have small (5-6 mm) and hooked teeth. Their skin is highly textured and covered with placoid scales, a mucus layer, and a semicircular caudal fin.

These huge sharks have a pointed snout that is distinctly hooked in juveniles. The dorsal fin of larger individuals can flop to one side when it breaches above the surface.

Range and Distribution

These giant sharks are found in the arctic and temperate waters of the world. In the western Atlantic, it ranges from Newfoundland to Florida and southern Brazil to Argentina, and from Iceland and Norway to Senegal, including the parts of the Mediterranean in the eastern Atlantic.

It is found off Japan, China, and Korea, as well as western and southern Australia and the coastlines of New Zealand in the western Pacific and from the Gulf of Alaska to the Gulf of California and from Ecuador to Chile in the eastern Pacific. Between May and October, they are found in British coastal waters. They migrate south as far as North Africa during the winter months. Transatlantic migrations of these sharks are also observed.

Habitat

They reside around the continental shelf and enter brackish waters occasionally. Living close to the water surface, including bays with narrow openings or at a depth of at least 2990 feet, these sharks follow plankton concentrations in the water column and are often visible at the surface. Waters of temperature between 8-14.5°C are preferred by them but are known to cross much warmer waters at the equator.

Diet

Basking sharks feed on small fishes like zooplankton and other invertebrates. They also eat copepods of the genera Pseudocalanus and Oithona.

They are filter-feeders who capture their prey by opening their mouth and allowing water to flow inside. Zooplankton and other species in the water are trapped in their gill rakers, from which they filter out tiny animals and consume them. In the process, they filter up to 4,000,000 pounds of water every hour.

Behavior

• Basking sharks are slow-moving sharks. They move at 3.7 km/hr.
• They are often seen soaking in the sunlight. 
• Most of the time, they are spotted alone, but sometimes with a group of single-sex individuals. 
• They do not evade approaching boats and are not attracted to chum
• When they feed, they move through the water and twist their bodies around, sometimes performing a full 360⁰ circle. 

Lifespan

These sharks have a long lifespan of about 50 years.

Adaptations

• Their gill rakers are used to catch prey.
• These sharks have a large mouth that helps them to strain plankton from the water.
• They have large livers that makeup 25% of their body weight, helping them store long-term energy and regulate buoyancy. 

Mating and Reproduction

These sharks are egg-laying species, with the developing embryos first relying on a yolk sac with no placental connection. They display oophagous behavior, with the embryos feeding on the mother’s unfertilized ova. Only one ovary functions in females, and it appears to be the right one.

The males and females live in different places and only come together to mate. Mating occurs in early summer. Pregnant females separate themselves from other females. After a gestation period of 2-3 years, a small number of young are born in late summer, fully developed at 1.5-2 m. Basking sharks are believed to produce the largest babies of all fish, just beating out the great white shark.

The juveniles possess a long, hook-like snout that helps them feed in the womb and early after birth by increasing the water flow through the mouth. Their mouth changes shape and length within a year after birth.

The mothers move into shallow waters after giving birth. They have a slow reproduction rate and are believed to take a 2-4 years break between litters. The newborns mature at the age of 6-13 when they are 15-20 feet long.

Predators

The only known predator of basking sharks is the great white shark. However, in California and New Zealand, killer whales feed on these sharks. Lampreys also try to feed on them, but cutting through the basking shark’s thick skin is a difficult task for their teeth.

Conservation Status

Basking sharks have been listed as “Endangered” or “EN” by the IUCN. Overfishing is their most common threat because people in countries like China and Japan use their cartilage for medicine, fins for shark fin soup, livers for oil, skin for leather, and flesh for food.

Climate change and global warming are other causes of their population decrease. As they are used to temperate water conditions, warming of waters due to the melting of polar ice caps will lead to habitat loss. Also, excess carbon dioxide in the air due to global warming can make the waters more acidic as the extra carbon dioxide in the atmosphere is absorbed by the sea. If the ocean becomes more acidic, sea creatures like coral or plankton, which are the food for basking sharks, cannot survive.

To prevent their extinction, ‘Convention on International Trade in Endangered Species of Wild Fauna and Flora’ (CITES) has made basking sharks a protected species in many countries. Buying and selling their body parts is also made illegal.

Interesting Facts

• Basking sharks are not afraid of boats or people. As a result, they swim close to divers. They are a valuable commodity for tourism as people enjoy watching them when on water.
• It is advisable to maintain a distance while observing basking sharks. According to experts, one should keep a distance of at least four meters from them while swimming and at least 100 meters if in a vehicle. 
• Their brain is the smallest of all sharks.
• On their upper and lower jaw, they have hundreds of small teeth that they do not use.
• They shed their gill rakers, which take up to five months to regrow. It is said that these sharks adopt near-bottom feeding when they shed their gill rakers.
• Basking sharks can open their mouth up to a meter wide.