Cetorhinus maximus

Geographic Range

Basking sharks ( Cetorhinus maximus ) have a wide geographic range and are most commonly found in temperate and boreal waters. In the Northern Hemisphere, basking sharks have been observed in the North Pacific Ocean, off the coast of Japan, as well as off the coast of China. This species has also been found inhabiting the North Atlantic Ocean and the Arctic Ocean. They have been found off the North Cape of Norway and off the coast of Russia. In the Southern Hemisphere, basking sharks have been reported off the coast of Brazil as well as near South Africa in the southern Atlantic Ocean. Basking sharks mostly inhabit neuritic zones (shallow areas on the continental shelf) during the summer, however they migrate to the offshore continental shelf during the winter.

• Biogeographic Regions
• ethiopian ethiopian
  • native native
• neotropical neotropical
  • native native
• oceanic islands oceanic islands
  • native native
• atlantic ocean atlantic ocean
  • native native
• pacific ocean pacific ocean
  • native native

Habitat

Basking sharks are a pelagic fish that inhabit a wide range of depths - from 200 to 2,000 m. They are usually found in subpolar and temperate waters moving south during the winter months (December to February). As the name states, basking sharks are commonly found at depths where sunlight reaches, usually dwelling in surface waters. They migrate inland to mate and feed during the summer. Throughout the year, basking sharks inhabits waters between 8 to 14°C.

• Habitat Regions
• temperate temperate
• polar polar
• saltwater or marine saltwater or marine

• Aquatic Biomes
• pelagic pelagic
• coastal coastal

Physical Description

Basking sharks are the second largest shark in the world, with an average adult size of 7 to 8 m in length, but occasionally adults reach 9 to 11 m. They have an average mass of 3,900 kg, and males are larger than females. Basking sharks have conical snouts and large gill slits behind their mouths that almost encircle their heads. On the front area of each gill arch, basking sharks have gill rankers ranging from 10 to 12 cm long. They have strong caudal keels located on their caudal peduncles, followed by crescent-shaped caudal fins.

Basking sharks have small teeth, just 3 to 4 mm long. Adult basking sharks have as many as 1,200 teeth, each with a single conical cusp in six rows in the upper and lower jaw. These sharks are grayish brown to black with pale white on their undersides, although mutations can cause blotchy areas. Two albino specimens have been reported in North Atlantic waters.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• male larger

Development

Basking sharks have a somewhat different ovary compared to other elasmobranchs. As female basking sharks reach sexual maturity, their ovaries begin to produce large amounts of small eggs, which contain a small amount of yolk. Their eggs closely resemble that of bony fish eggs. Females lay approximately 6 million small eggs averaging 2 mm in diameter. As these eggs begin to mature, they move through a system of narrow, complex canals leading towards the uterus. Baskings sharks have large uteri lined with thousands of threadlike projections called trophonemata. These help nourish embryos after fertilization, as in every other viviparous elasmobranch. These newly-fertilized embryos develop into juvenile basking sharks, then feed on unfertilized eggs in utero until it is time for female basking sharks to deliver their pups.

Reproduction

Basking sharks move into coastal areas during the breeding season (May to July). Once inshore, basking sharks begin courtship behaviors. This species is polygynandrous, meaning both females and males have multiple mates. Very little is known about courtship behavior in sharks, especially pelagic species. As of today, 380 shark species have been discovered, but only nine species have been studied for their courtship, pairing, copulation, and post-copulatory behaviors. Females basking shark shave been observed breaching, giving a small insight on the behaviors involved in selecting mates. Breaching occurs when females leap meters out of the water then land, elaborately creating an outward surge of water. Scientists have determined this behavior is one way females attract males. this breaching behavior demonstrates that female basking sharks are ready to mate.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Males have a breeding season from May to July. It is demonstrated that basking sharks are ovoviviparous which means pups hatch from eggs while still inside their mother’s womb, then proceed to develop before being born. Embryos are completely nourished by the yolk in their eggs. As embryos develop into juvenile basking sharks and hatch, these infant basking sharks feed upon unfertilized eggs in utero.

At birth, basking shark pups have an average size of 2 m and immediately swim away from their mother. As development continues, sexual maturity is obtained when males reach 4.6 to 6.1 m – around 8 years old. Females reach maturity at 8.1 to 9.8 m, or after about 11.5 years.

Female gestation times last about three years, based on vertebral ring count. It is believed female basking sharks live somewhat hidden lifestyles for three consecutive years.

• Key Reproductive Features
• seasonal breeding seasonal breeding
• sexual sexual
• fertilization fertilization
  • internal internal
• ovoviviparous ovoviviparous

As basking shark embryos develop in the wombs of females, nutrients are given through threadlike projections called trophonemata, which are used to nourish embryos after fertilization, as in every other viviparous elasmobranch ( Elasmobranchii ). After basking shark pups are delivered, they immediately swim away from their mothers.

• Parental Investment
• no parental involvement
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

Maximum lifespan of basking sharks in the wild is roughly 32 years. This number was obtained using vertebral ring counts. Parker and Stott (1965) found that basking sharks can reach the 32 vertebral ring count by an average age of 17.5 years. Researchers believe basking sharks gains two vertebral rings annually. There is no information available on basking shark longevity in captivity.

Behavior

Basking sharks migrate mostly based on the abundance of plankton. In the North Atlantic Ocean, basking sharks migrate north while food resources remain high. As the amount of plankton begins decreases around the beginning of winter, basking sharks then move southward in search of new areas to feed. Basking sharks may migrate as far as the northern coast of South America as well as South Africa. Cotton et al. (2005) report that basking sharks have forging patterns based on thermal fronts. These thermal fronts are known to have high populations of zooplankton due to higher water temperatures.

Basking sharks have demonstrated a behavior known as breaching. Breaching happens when they leap out of the water, with reports of 182 cm distance between their tails and the ocean surface. This behavior is most commonly displayed during mating season, from May to July. It is thought that females do this to announce receptivity of mating.

• Key Behaviors
• natatorial natatorial
• motile motile
• nomadic nomadic
• migratory migratory
• social social

Home Range

Home ranges have not been reported for this shark. They are not known to defend a territory.

Communication and Perception

Not much is known about the perception and communication of basking sharks. Like other sharks, it is believed that they have keen chemoreceptors and electroreceptors around their snout, which they use to detect plankton. Their chemosensory detectors are believed to detect dimethyl sulfide released by phytoplantkon as they are eaten by larger predatory zooplankton. Basking sharks then feed on these larger zooplankton. Basking sharks demonstrate visual communication behaviors and breaching, which is used during the mating season to communicate to males that females are ready to mate.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Perception Channels
• visual visual
• chemical chemical
• electric electric

Food Habits

Basking sharks are selective foragers, concentrating their feeing activity along thermal fronts with high densities of zooplankton. To feed, thes megaplanktivores swim with their mouths open, closing their jaws every 30 to 60 seconds. After collecting water, gill rakers filter the water through five large gills, capturing plankton. Basking sharks filter an average of 6,000 L of water per hour. Their stomach matter includes other small copepods such as Psuedocalanus and Oithona , but it is certain the basking shark is an indiscriminate plankton feeder.

• Primary Diet
• carnivore carnivore
  • eats non-insect arthropods
• planktivore planktivore

• Animal Foods
• aquatic crustaceans
• zooplankton zooplankton

• Foraging Behavior
• filter-feeding filter-feeding

Predation

Basking sharks have been noted to have one major predator: Homo sapiens (humans). Thousands of basking sharks are caught per year by fisheries around the world. There is also documentation of great white sharks ( Carcharodon carcharias ) feeding on carcasses of basking sharks, but it is unknown whether or not the basking sharks were killed by those great white sharks.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

Basking sharks have been known to leap out of the water in efforts to dislodge lampreys and copepods that attach themselves to these large sharks. These are the only parasitic relationships that have been noted among basking sharks. Basking sharks also have a mutualistic relationship with pilot fish ( Carangidae ). These fish swim alongside basking sharks and clean harmful parasites, such as the large copepods ( Dinematura producta ) from their bodies.

Economic Importance for Humans: Positive

Basking sharks have extremely large livers that makes up most of its mass. The livers of basking sharks hold useful oils that humans use. These oils are most commonly found in cosmetic supplies, such as lotions and hair products. Because this oil is economically important for the cosmetic industry, it has inevitably put the basking shark into a vulnerable state due to their increased capture rate by fisheries.

• Positive Impacts
• food food
• body parts are source of valuable material

Economic Importance for Humans: Negative

Basking sharks have hindered some fishery industries by becoming entangled in their nets, causing them to rip. This negatively impacts fisheries economically when each net is replaced.

Conservation Status

As a large, slow moving, surface-feeding species, basking sharks normally come into contact with humans. This contact has increased the mortality of basking sharks due to the commercial fishery harvesting their livers. The recognition of the negative impact of shark finning on the aquatic environment has led to laws being established by the federal government to keep this species protected. The Convention on International Trade in Endangered Species (CITES) has listed the basking shark in Appendix II, which means that the monitoring of basking shark trading is carefully watched and, if need be, facilitation will occur in order to get fisheries involved. Basking sharks are heavily protected within 22.2 km of the Isle of Man and Guernsey as well as in British waters by wildlife legislation. Furthermore, the National Marine Fisheries Service has enacted a rule prohibiting direct commercial capturing and sale of this species in the waters of the United States. The Shark Trust has established a code of conduct for boaters that encounter basking sharks, ensuring that the sharks will have minimal disturbance. Boaters must slow their vessels and carefully pass until any basking sharks have cleared the area.

Additional Links

Encyclopedia of Life

Contributors

Logan Powell (author), Radford University - Fall 2015, Cari Mcgregor (editor), Radford University, Zeb Pike (editor), Radford University, Karen Powers (editor), Radford University, April Tingle (editor), Radford University, Jacob Vaught (editor), Radford University, Galen Burrell (editor), Special Projects.

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