Basking shark characteristics, habitat, feeding, reproduction

2969
Simon Doyle

The basking shark (Cetorhinus maximus) is a fish that is part of the Cetorhinidae family. It is the second largest shark in the world, and can measure up to 12 meters. However, its average length is 6.7 to 8.8 meters.

Another peculiarity of this species is that its feeding occurs by filtration. For this, the shark has adaptations in its teeth, which allow it to act as a sieve when water enters the oral cavity. In addition, it has long slits and gill rakes, which facilitate the filtering process..

Basking shark. Source: Green Fire Productions [CC BY (https://creativecommons.org/licenses/by/2.0)]
In relation to its distribution, the basking shark is found in temperate and subpolar waters around the world. However, this species rarely frequents the equatorial marine waters..

Article index

  • 1 Brain
  • 2 Features
    • 2.1 Size
    • 2.2 Head
  • 3 Habitat and distribution
    • 3.1 Distribution
    • 3.2 Habitat
  • 4 Taxonomy
  • 5 Conservation status
    • 5.1 Threats
    • 5.2 Actions
  • 6 Food
    • 6.1 Variations during the seasons
  • 7 Playback
  • 8 Behavior
  • 9 References 

Brain

A group of researchers carried out a research work on the brain of the Cetorhinus maximus. According to the results, it presents a primitive level in the development of the brain, which is reflected in its motor and sensory abilities and capacities..

In addition, considering the relationship between body weight and the brain, this organ has the lowest degree of cerebralization than the rest of the sharks that have been studied. Likewise, externally it has certain morphological characteristics that are unique to its species..

In this sense, the proportions of the parts of the brain correspond to the cerebral organization of primitive vertebrates. Thus, the telencephalon, which corresponds to 34% of the total brain mass, is the same size as that of other sharks.

In contrast, the cerebellum, which accounts for 30% of brain mass, is significantly larger than any other shark. In addition, the C. maximus It presents some peculiarities in relation to nuclear expansion in the telencephalon. In this sense, the caudal interhemispheric region is very large.

Characteristics

The basking shark differs from the rest of the shark by the large gill slits that are found around the head. In addition, it has long gill rakes, which facilitate filter feeding.

In relation to the caudal peduncle, it has strong lateral keels. The tail fin is shaped like a crescent. The body is covered with placoid scales. These are small, conical and curved towards the rear end of the animal.

In terms of coloration, shark is usually grayish brown, black, lead blue or gray. It generally has white spots, irregularly distributed on the belly and on the head.

On the other hand, the Cetorhinus maximus it has a large liver, which can represent up to 25% of its body weight. This organ has a high level of squalene. This is a low-density hydrocarbon that contributes to the regulation of the animal's buoyancy..

Size

This species is the second largest shark, after the whale shark (Rhincodon typus). The basking shark's body can reach lengths of up to 12 meters, with a body mass of 16 long tons. However, an average adult measures between 6.7 and 8.8 meters. At birth, its size ranges from 1.5 to 1.8 meters.

Its development is slow, being able to grow from 5 to 6 meters before reaching sexual maturity. In relation to weight, it is around 4,000 kilograms.

Head

The basking shark's snout is pointed and the mouth is large, with a sub-terminal location. The denture is small and is made up of many teeth. Those located in the center of the jaw are low and triangular in shape, while those on the sides are conical and curved backwards..

In general, there is a large space in the central area of ​​the upper jaw, where the teeth are scattered.

A characteristic feature of this shark is that, in the juvenile stage, the snout is long and hooked. Experts suggest that this structure is used to feed within the uterus and after birth. In particular, the mouth changes its length and shape during the first year of life..

Habitat and distribution

Distribution

The Cetorhinus maximus It is distributed in sub-polar and temperate waters worldwide. On very few occasions it is sighted in equatorial water. Thus, in the North Atlantic, it inhabits from the transition zone between the waters of the Arctic and the Atlantic to the Mediterranean..

In this region it also lives to the west and south of Iceland, in the Gulf of Maine and the area off Russia and in the North Cape of Norway. As for the Western Atlantic Ocean, it runs from Canada to Florida, including Newfoundland. Also, it extends from southern Brazil to Argentina..

In relation to the eastern Atlantic, it is located in Norway, Iceland and the western part of the Barents Sea to Senegal and the Mediterranean. In the Western Pacific, the basking shark is distributed from Japan to New Zealand.

This shark also lives in the Eastern Pacific, being found from the Gulf of Alaska to Chile, being able to be located in the Galapagos Islands.

According to experts, the morphological differences that exist between basking sharks that live in the North and South Atlantic oceans and those that are in the Pacific do not suggest the existence of separate species. Evidence indicates that these are geographically isolated populations.

Habitat

The basking shark inhabits island and continental shelves, in coastal waters, the high seas, and in closed bays. In these areas, it can be found in pairs, in groups of more than three sharks or forming large schools of fish..

It normally prefers waters with a temperature ranging between 8 and 14 ° C, however, in New England it lives in seas of up to 24 ° C. When the climatic conditions are ideal, this shark frequently heads to the surface of the continental shelf and to the edge of the shelf..

However, it usually makes extensive horizontal and vertical migrations, reaching deeper areas. These trips are made in order to have access to the most productive feeding areas.

Taxonomy

-Animal Kingdom.

-Subkingdom: Bilateria

-Phylum: Chordate.

-Subfilum: Vertebrate.

-Infrafilum: Gnathostomata.

-Superclass: Chondrichthyes

-Class: Chondrichthyes.

-Subclass: Elasmobranchii.

-Superorder: Euselachii.

-Order: Lamniformes.

-Family: Cetorhinidae.

-Genus: Cetorhinus.

-Species: Cetorhinus maximus.

State of conservation

Basking shark populations are declining, mainly due to overfishing. This situation has caused the IUCN to include this species within the group of animals that are at high risk of becoming extinct..

Threats

The Cetorhinus maximus it has been heavily exploited for several centuries. The man hunts it to commercialize the oil that is extracted from his liver, which is used in lighting and industrial purposes. Also, it uses the skin to make leather articles and the meat is part of exquisite dishes of the local gastronomy.

In addition, the fins and cartilage are used in the production of fishmeal. The huge fins of this species are sold at very high prices in various shops in East Asia..

When the animal is on the surface, it is captured by directed fisheries using non-explosive harpoons. Also, these sharks become incidentally entangled in the fishing nets of other species..

The volume of basking shark hunting is associated with the supply and demand of the by-products obtained from it. Thus, the fall in the market in the prices of liver oil and fins causes the shark fishery to decrease or increase..

Actions

Various organizations, both national and international, have established measures that favor the conservation of biodiversity and the management of fisheries.

In this way, since 2007, the basking shark has been protected in the territorial waters of the member states of the European Union. Those who inhabit the Mediterranean Sea have been protected since 2012.

The Cetorhinus maximus it is listed in numerous international agreements, including Appendix II of CITES. This implies that international trade must be monitored and the species will only be obtained by those fisheries managed in a sustainable way..

Likewise, this shark is listed in Appendices I and II of the CMS (Convention on the Conservation of Migratory Species). Inclusion in Appendix I requires signatory parties to protect basking shark within territorial waters.

CMS Appendix II urges governments to take cooperative action around its preservation as a species.

Feeding

The basking shark feeds on small fish, zooplankton, barnacles, copepods, eggs, and fish larvae. This shark is filter feeder, as do the whale shark and the broadmouth shark..

However, the Cetorhinus maximus it is the only one that does so using the passive flow of water through its pharynx, while moving in the ocean. The other two sharks actively pump or suck water into the pharynx..

In this way, to capture its prey, the elasmobranch swims slowly across the surface of the water, or very close to it. As it moves, its huge mouth is held open, for about 30 to 60 seconds. Periodically closes the oral cavity, strongly contracting the gill arches.

This is probably done to expel as much water as possible from the mouth. The water is directed against the gill spines, which are erect and extended through the gaps in the gill arches..

Thus, a kind of tapestry is formed, which retains the prey contained in the seawater. The basking shark can filter up to 2,000 tons of seawater every hour.

Variations during the seasons

During the summer, this species feeds in shallow water, while in the winter it is found in deep water. Previously there was the hypothesis that, during this cold time of year, the shark stopped feeding, obtaining nutrients from the reserves contained in the liver.

However, innovative energy studies indicate that, during the cold season, the animal continues to feed regularly. For which, they carry out extensive vertical and horizontal migrations, on the continental shelf of the northeastern Atlantic..

Experts point out that, in the deep ocean, basking sharks could feed on fish or copepod eggs.

Reproduction

The male reaches sexual maturity between 12 and 16 years, when his body measures around 5 and 7 meters. As for the female, it can reproduce at an estimated age of 16 to 20 years, having a body length of 8.1 to 9.8 meters.

Mating occurs in early summer. During courtship, the pair go to shallow waters, exhibiting various behaviors. These include parallel swimming, fin biting, and gently nudging each other. In addition, the male is often positioned over the female.

This species is ovoviviparous, since the eggs remain inside the female's uterus, until the embryo is fully developed. Like other sharks, a single ovary is functional, containing a large number of eggs..

As for the embryos, they develop because they absorb the yolk sac, however, once it has been completely consumed, they can feed on other eggs produced by the mother.

The pregnant female migrates to deeper waters, where she remains for about 12 to 36 months. In relation to the litter, it can be up to 6 young, which are born measuring between 1.5 and 2 meters.

Behaviour

The basking shark makes long transoceanic migrations, moving for example from the British Isles to Newfoundland, in Canada. Likewise, they tend to move in the meso-pelagic waters between the northern and southern hemispheres..

During these movements, they can travel up to 9,000 kilometers, organized in large groups, which could be segregated by sex or size..

The seasonal migrations of this species are associated with the superficial abundance of zooplankton. The Cetorhinus maximus tends to move north in the summer, while heading south during fall and winter.

The vertical use of the habitat varies, especially when moving towards the coast. In the area close to this, most of the time the shark remained in the mixed layer. However, the basking shark usually spends long periods in cold waters..

In relation to the high seas, the movements depend on the location. Thus, the species that are found in Hawaii, remain much longer in the depth of the ocean than those that live in Baja California.

References

  1. Kruska DC (1988). The brain of the basking shark (Cetorhinus maximus). Recovered from ncbi.nlm.nih.gov.
  2. Knickle, L. Billingsley, K. DiVittorio (2020). Cetorhinus maximus. Recovered from floridamuseum.ufl.edu.
  3. Street, R. (1999). Cetorhinus maximus. Animal Diversity Web. Recovered from animaldiversity.org.
  4. Sims, D., Fowler, S.L., Clò, S., Jung, A., Soldo, A., Bariche, M. (2016). Cetorhinus maximus. The IUCN Red List of Threatened Species 2016. Recovered from iucnredlist.org.
  5. Fowler, S.L. (2009). Cetorhinus maximus. The IUCN Red List of Threatened Species 2009. Recovered from iucnredlist.org.
  6. EDGE (2020). Cetorhinus maximus. Recovered from edgeofexistence.org.
  7. Bray, D.J. (2018). Cetorhinus maximus. Fishes of Australia. Recovered from fishesofaustralia.net.au.
  8. Heidi Dewar, Steven G. Wilson, John R. Hyde, Owyn E. Snodgrass, Andrew Leising, Chi H. Lam, Réka Domokos, James A. Wraith, Steven J. Bograd, Sean R. Van Sommeran, Suzanne Kohin (2018) . Basking Shark (Cetorhinus maximus) Movements in the Eastern North Pacific Determined Using Satellite Telemetry. Recovered from frontiersin.org.

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