Basking Sharks: Characteristics, Behavior, Size , Feeding and Mating

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Basking shark
Basking sharks (Scientific name: Cetorhinus maximus) are the second largest fish in the world after whale sharks. Also known as bone sharks, because you can see the bones inside their bodies when their mouth are opem, which is most of the time, they glide through the open sea in cool to warm temperate oceans straining plankton in their open mouths. The species most common name is derived from people who saw it and thought is was basking in the sun. Other names include elephant shark, sail-fish, and sun-fish. In Orkney it is called hoe-mother, meaning "the mother of the picked dog-fish".

Basking sharks are one of three plankton-eating shark species, along with whale sharks and megamouth sharks. Basking sharks can reach lengths of 20 meters and weigh up to six tons. One fisherman pulled up a basking shark that was so large he thought it was a plesiosaur. Like whale sharks it is non aggressive and offers no threats to humans.

In 2003 basking sharks were declared an endangered species by The United Nations Convention on International Trade on Endangered Species (CITES) and international trade restrictions on them were imposed. It is not known how many of them there are but their numbers are believed to be decreasing.

Basking sharks can live up to roughly 32 years, with and an average age of 17.5 years, in the wild. These figures were arrived at using vertebral ring counts. Researchers believe basking sharks gains two vertebral rings annually. [Source: Logan Powell, Animal Diversity Web (ADW)]

Websites and Resources: Shark Foundation ; International Shark Attack Files, Florida Museum of Natural History, University of Florida ; Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Fishbase ; Encyclopedia of Life ; Smithsonian Oceans Portal

Basking Shark Habitat and Where They Are Found

Basking shark live in temperate, subpolar, saltwater, marine environments and are found in coastal areas and in the open ocean typically at depths of 200 to 2000 meters (656 to 6562 feet) but also in depths so shallow their fins and mouth pierce the surface, in waters between eight to 14°C ( 46 to 57̊F). [Source: Logan Powell, Animal Diversity Web (ADW) /=]

Basking shark range

Basking sharks have a wide geographic range and are most commonly found in temperate and waters in northern latitudes. In the Northern Pacific Ocean, they have been spotted off the coasts of Japan and coast of China. In North Atlantic Ocean and the Arctic Ocean, they have been observed off coasts of Ireland and Britain, the North Cape of Norway and off the coast of Russia. In the Southern Hemisphere, basking sharks have been reported off the coasts of South Africa and Brazil and the southern Atlantic Ocean.

Basking sharks mostly inhabit shallow areas on the continental shelf during the summer and migrate off of continental shelves during the winter. They are usually found in subpolar and temperate waters moving southward direction during the winter months (December to February). At the same time, as their name suggests, basking sharks are commonly found at shallow depths with penetrating sunlight. They migrate towards land to mate and feed during the summer.

Basking Shark Characteristics

Basking shark reach lengths from 11 meters (36 feet), with their average length being seven meters (23 feet). Their average weight is 3900 kilograms (8590.31 pounds). Males are larger than females. A 12.27 meter (40.3 foot) specimen trapped in a herring net in the Bay of Fundy, Canada, in 1851 is recognized as the largest recorded basking shark. Its weight has been estimated to be 16 tonnes (18 tons). [Source: Wikipedia, Logan Powell, Animal Diversity Web (ADW) /=]

The basking shark is the only extant member of the family Cetorhinidae, part of the mackerel shark order Lamniformes. The oldest known members of Cetorhinidae are members of the extinct genus Keasius, from middle Eocene (47.8 million to 3.8 million years ago). Colouration is highly variable. Individuals can be grayish brown to black with pale white on their undersides, although mutations can cause blotchy areas. Two albino specimens were seen in the North Atlantic waters.

According to Animal Diversity Web: Basking sharks have conical snouts, distinctly hooked in younger specimens, 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 centimeters long. They have strong caudal keels located on their caudal peduncles, followed by crescent-shaped caudal fins. They have massive livers, which make up a quarter of their mass.

Other distinctive basking shark characteristics include highly textured skin covered in placoid scales and a mucus layer. In large sharks, the dorsal fin may flop to one side when above the surface. The sharks are often noticeably scarred, possibly through encounters with lampreys or cookiecutter sharks. The basking shark's liver runs the entire length of the abdominal cavity and is thought to play a role in buoyancy regulation and long-term energy storage. [Source: Wikipedia]

Basking Shark Behavior

Basking sharks are motile (move around as opposed to being stationary), nomadic (move from place to place, generally within a well-defined range), migratory (make seasonal movements between regions, such as between breeding and wintering grounds), and social (associates with others of its species; forms social groups). Home ranges have not been reported. They are not known to defend a territory. [Source: Logan Powell, Animal Diversity Web (ADW) /=]

Basking shark size

Basking sharks are usually solitary but during summer months in particular places with large concentrations of zooplankton they engage in social behaviour. They can form sex-segregated shoals, usually in small numbers (three or four), but up to 100 individuals have been reportedl. Small schools in the Bay of Fundy and the Hebrides have been seen swimming nose to tail in circles in summer months. This behavior has been studied and may be a courtship ritual. [Source: Wikipedia]

Basking sharks communicate with vision, touch and chemicals usually detected by smelling and sense using vision, electric signals and chemicals detected by smelling. They have been observed breaching — leaping out of the water — sometimes a considerable distance for such a large shark. There are reports of them clearing the water with a distance of 1.8 meters (six feet) between 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. Basking sharks also have been known to leap out of the water in efforts to dislodge lampreys and copepods that attach themselves to the massive sharks. Basking sharks also have a mutualistic relationship with pilot fish, which swim alongside basking sharks and clean harmful parasites, such as the large copepods. /=\

Basking Shark Food and Feeding

Basking sharks takes in large amounts of water and plankton. As water is expelled out of the large gill slits, mucus laden gill rakers trap the plankton, which the shark quickly digests. To feed, they 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 have small three-to-four millimeter long teeth. Adults have as many as 1,200 teeth, each with a single conical cusp, positioned in six rows in the upper and lower jaws.

Basking sharks swim at a top speed of about five kilometers per hour (three miles per hour) but generally cruise around a little slower than that filtering plankton from about 450 tonnes (500 tons) of water an hour. The shark cruise around with their mouthes agape, sometimes leaning to one side or rolling completely upside down.

Basking sharks mainly eat aquatic crustaceans and zooplankton. They are selective foragers, concentrating their feeding activity along thermal fronts with high densities of zooplankton. Thermal fronts are known to have high populations of zooplankton due to higher water temperatures. Examinations of their stomach contents typically reveal small copepods such as Psuedocalanus and Oithona. Some basking shark are indiscriminate plankton feeders taking in plant as well as animal material. [Source: Logan Powell, Animal Diversity Web (ADW)]

Atlantic basking shark

Basking Shark Feeding Behavior

According to Animal Diversity Web: Basking sharks migrate mostly based on the plankton supply in the water. In the North Atlantic Ocean, they migrate north while food resources remain high. As the amount of plankton begins decreases around the beginning of winter, they migrate southward in search of new sources of food. Basking sharks may migrate as far as the northern coast of South America as well as South Africa. [Source: Logan Powell, Animal Diversity Web (ADW) /=]

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 migrates over large distances in the Atlantic and Pacific. They are mostly solitary but sometimes will gather in large groups when a large source of food is available. Basking sharks show up in seas off of Britain and are studied by the Basking Shark Project. Some sharks have been tagged with electronic tags that help scientists track their movements and get some insight into their behavior. In the seas off England and Ireland the sharks often show up to feast on calanoid copepods. Sometimes 50 to 100 sharks will show when calanoid copepods appear in numbers feed on plankton blooms.

The feeding habits of basking sharks confirms a theory for a search strategy first proposed by the French mathematician Paul Pierre Levy that states the best strategy for finding something (food in this case) is to alternate between long extended leaps and intense clustering around certain spots. A study by David Sims of the Marine Biological Association of Plymouth found that for the most part basking sharks do this.

Migration of Basking Sharks in Western Atlantic Ocean

The Christian Science Monitor reported: Until 2009 the conventional wisdom was that tropical waters presented a barrier to basking sharks as they migrated north and south each year. Marine biologist Elliott Norse who heads the Marine Conservation Biology Institute in Bellevue, Washington said traditionally you looked to the temperate oceans for basking sharks and to tropical oceans for whale sharks. But a team led by Dr. Gregory Skomal, a marine biologist with the Massachusetts Division of Marine Fisheries, tracked basking sharks from the start of their journey in waters off southeastern Canada and the northeastern U.S. all the way to the coasts of Brazil, well into the southern hemisphere. Until now, the farthest south the creatures had been tracked was to waters off the U.S. Southeast. [Source: Pete Spotts, Christian Science Monitor, May 12, 2009]

In some respects, their migration patterns along the east coast of North America track those of the endangered Atlantic right whale. The sharks and whales hang out off southeastern Canada, in the Gulf of Maine, and off Massachusetts in the summer, then many head south in the fall.

Scientists have tracked many of the right whales to wintering grounds off the southeastern U.S., but the basking sharks just vanish. So do anywhere from 25 to 50 percent of the right whales. "The winter disappearance of the basking shark has been a conspicuous topic in the scientific literature for a hundred years," Skomal explains. By finding the missing sharks, scientists suspected they might also find some of the missing whales.

To track the sharks, Skomal and his team from the University of New England, the Woods Hole Oceanographic Institution, and state fisheries agencies in Massachusetts and Maine, applied pop-up tags to 25 sharks. The tags, essentially narrow tubes about eight inches long, measure light levels, water temperature, and depth every 10 seconds. They store the data, which is sent back to the lab via satellite after a tag releases itself from the fish and bobs to the surface.

Out of 25 tags, the team got data back from eight, spanning periods ranging from 12 to 234 days. The sharks migrated from New England to the Bahamas, Puerto Rico, and off the coast of Venezuela. Stunningly, two ended up below the equator in along the coast of Brazil. Moreover, as they traveled, the sharks often dove to depths of between 800 and 1,000 meters (2,625 and 3,281 feet) . Some stayed there for up to five months.

At such depths, the light sensors are useless. The sensors allow marine biologists to use sunlight to estimate an animal's position and reconstruct its migration path. So the research team used oceanographic maps of temperatures in different masses of water — which at those depths remain remarkably stable over time — to reconstruct the sharks' paths in more detail than merely saying they started here and finished there. Results of this research was published in the journal Current Biology in 2009 .

Basking Shark Mating, Reproduction, Offspring and and Offspring

Basking sharks are ovoviviparous (also called aplacental viviparous), meaning that eggs are hatched within the body of the parent. They engage in internal reproduction in which sperm from the male fertilizes the egg within the female. Embryos develop in the wombs of females. Nutrients are given through threadlike projections called trophonemata, which begins nourishing embryos after fertilization, as is the case with all sharks and rays (elasmobranchs) that incubate eggs inside their body and give birth to live offspring.[Source: Logan Powell, Animal Diversity Web (ADW) /=]

According to Animal Diversity Web: Basking sharks have a somewhat different ovary compared to other sharks and rays. As females reach sexual maturity, their ovaries begin to produce large amounts of small eggs, which contain a small amount of yolk. These eggs closely resemble the eggs of bony fish. Females lay approximately six million small eggs averaging two millimeters 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, which nourish embryos after fertilization (See Above).

Basking sharks breed once every year during the warmer months of May to July, with the average number of offspring being four. The average gestation period is 36 months based on vertebral ring counts. It is believed female basking sharks live somewhat hidden lifestyles during the three years of their gestation period. Pre-birth stage provisioning and protecting is done by females. There is no parental involvement after birth. On average females reach sexual or reproductive maturity at age 11.5 years and males reach sexual or reproductive maturity at eight years.

Basking sharks are polygynandrous (promiscuous), with both males and females having multiple partners. According to Animal Diversity Web: They sharks move into coastal areas during the breeding season. Once inshore, basking sharks begin courtship behaviors. Females basking sharks have been observed breaching (leaping out of the water) during the breeding season. They sometimes leap meters out of the water and create an outward surge of water when they land. Scientists believe this is a signal by the female that she is ready to mate.

Pups hatch from eggs while still inside their mother’s womb and 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. After basking shark pups are delivered, they immediately swim away from their mothers. At birth, basking shark pups have an average size of two meters (6.5 feet). Males reach sexual maturity when they are 4.6 to 6.1 meters (15 feet to 20 feet) in the length — around age eight years old. Females reach maturity at 8.1 to 9.8 meters (26.5 to 32 meters) — after about 11.5 years. /=\

Humans, Basking Sharks and Conservation

Basking sharks have only real predator — humans. Thousands of basking sharks are caught very year by fisheries around the world. There have been some reports great white sharks feeding on carcasses of basking sharks, but it not known whether the basking sharks were killed by the great white sharks or were already dead when the great whites arrived. [Source: Logan Powell, Animal Diversity Web (ADW) /=]

As a large, slow moving, surface-feeding species, basking sharks normally come into contact with humans. Because basking sharks have huge livers that hold oils that humans use they are sought after by commercial fishing operations. These oils, which have a high squalene content, are commonly found in cosmetics, lotions and hair products. The demand for these oils has led to pressures to catch the fish and possible population declines. Their fins are also desired in East Asia for shark fin soup. Parts (such as cartilage) are also used in traditional Chinese medicine and as an aphrodisiac in Japan. Basking sharks use to be so abundant their flesh was used for fishmeal and their hide for leather. ,

Basking sharks are categorized as endangered on the International Union for Conservation of Nature (IUCN) Red List. The Convention on International Trade in Endangered Species (CITES) places the sharks in Appendix II, which lists species not necessarily threatened with extinction now but that may become so unless trade is closely controlled. /=\

Basking sharks are protected in British waters, particularly the area within 22.2 kilometers of the Isle of Man and Guernsey, by British wildlife legislation. The U.S. National Marine Fisheries Service has enacted regulations prohibiting direct commercial capturing and sale of basking sharks in U.S. waters. The Shark Trust has established a code of conduct for boaters that is similar to that for whales. If a boater encounter basking sharks, to ensure that the sharks are have minimally disturbed, the boaters must slow down until they are no basking sharks in sight.

Studying Basking Shark in the Eastern Atlantic

Oceanographer Alexandra Rohr of the French research outfit APECS has also tagged and is tracking basking sharks. She said they can disappear into the depths for several months at a time before resurfacing, swimming as deep as 900 meters (around 3,000 feet). According to Nature: During these epic dives, transmitters attached to the sharks record their underwater movements for months at a time, and then transmit data to satellites when the animals come up to the surface time. [Source: Peter Dockrill, Nature 20 August 2018]

Fishermen and divers often help locate sharks to tag. "I just saw the tip of his fin," fisherman Alain Quemere, who encountered a basking shark off the coast of Brittany in France's northwest, told AFP. "One moment it grazed the front of the boat, which made me laugh because my boat is barely five and a half meters and the shark was eight."

One insight from the project is just how migratory these sharks actually are. One female monitored in the study swam from Scotland to the Canary Islands, then to the Bay of Biscay, all in less than a year. As AFP reports, seven basking sharks have been tagged with the transmitters since 2016, and while sightings in the region are generally rare — especially during winter — every time one of these giant sharks emerges is a chance for us to learn a little bit more about them.

Image Source: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023

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