Sharks & Rays
Basking shark
Cetorhinus maximus
ALSO KNOWN AS
Bone shark, elephant shark
DISTRIBUTION
Worldwide in warm to cold temperate latitudes; absent from the tropics and polar regions
ECOSYSTEM/HABITAT
Coastal to open ocean
FEEDING HABITS
Filter feeder
TAXONOMY
Order Lamniformes (mackerel sharks and relatives); Family Cetorhinidae (basking sharks)
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Basking sharks are the second largest fish in the world, coming second only to whale sharks. Reaching lengths of 12 metres, basking sharks can give an intimidating impression. They are harmless to humans though because, much like whale sharks, they are filter feeders. These sharks get their name from their appearance of ‘basking’ at the sea surface, where they spend most of their time swimming with their extraordinarily large mouths open, filtering out their preferred prey: plankton and small crustaceans. Despite their large size, there are still large knowledge gaps about their life history; basking sharks are widely distributed throughout the world’s oceans and do not stay in any one place for longer than a few months. One thing we do know for sure – these sharks are gentle giants and witnessing one in the wild is something to behold.
Basking sharks are the second largest fish in the world, coming second only to whale sharks. Reaching lengths of 12 metres, basking sharks can give an intimidating impression. They are harmless to humans though because, much like whale sharks, they are filter feeders. These sharks get their name from their appearance of ‘basking’ at the sea surface, where they spend most of their time swimming with their extraordinarily large mouths open, filtering out their preferred prey: plankton and small crustaceans. Despite their large size, there are still large knowledge gaps about their life history; basking sharks are widely distributed throughout the world’s oceans and do not stay in any one place for longer than a few months. One thing we do know for sure – these sharks are gentle giants and witnessing one in the wild is something to behold.
Basking sharks are one of three plankton-eating species of sharks. Their filter feeding lifestyle allows them to be slow moving and spend much of their time at the sea surface, which is why they have been named the ‘basking’ shark. They are specially adapted to filter feeding, with huge mouths and highly developed gill rakers, bristle-like branches, that extend from their gills to help catch tiny prey. Basking sharks still have lots of teeth, but they are very small.
Basking sharks can be distinguished from other sharks by their large size as well as by their enormous gill slits that practically encircle their whole head. They also have long conical snouts and a distinct dorsal fin in the shape of a 45-degree angle triangle that is slightly rounded along the top. Their caudal or tail fin is crescent shaped. Basking sharks are greyish-brown in colour and appear to have mottled skin. They can grow to 12 metres long and weigh up to 4.5 metric tons.
There are a lot of unknowns around the birthing habits of basking sharks. Information on average litter size comes from one pregnant female carrying six young that was caught by a fisher. Gestation has been estimated at two and a half to three and a half years, the longest gestation known for any animal. In fact, basking sharks are even believed to give birth to the largest offspring of any fish; the minimum recorded size of basking sharks observed in the wild is two metres long. Scientists believe that male and female basking sharks live in different areas and likely only come together to mate. It is also thought that pregnant females separate from other females during gestation, based on the fact that nearly every individual observed or caught near the ocean’s surface is a female that is not pregnant. Along with their long gestation periods and late age of maturity, basking sharks are a long-lived species of shark and are estimated to live to 50 years of age.
Basking sharks have a large distribution throughout the world’s oceans. They are one of a few species that lives in temperate latitudes, both north and south of the equator, but not in between in the tropics nor in the polar regions. However, scientists believe that the populations in both these temperate zones belong to the same species, so it is likely that at least some individuals move back and forth between the two hemispheres without ever coming to the surface. There are some places in their range where basking sharks are an uncommon sight and are solitary, whereas other areas and at certain times of the year they can be commonly seen swimming together in large groups of 30 to 1400 individuals!
Basking sharks were historically targeted in Canada for liver oil by fisheries that operated in the 1940s. There was also an eradication program in western Canada in the 1940s and 1950s led by the government in response to the belief that they were a nuisance to commercial salmon fishing operations. Not surprisingly, these efforts are believed to be responsible for the near disappearance of basking sharks off the west coast of Canada. Elsewhere, they have been targeted by fisheries as a source of food, animal feed and for their shark fins.
Today, basking sharks in Canada are most at risk from entanglements in fishing gear or as bycatch in other fisheries. They are also targeted in other parts of their range due to the high value of their fins which has promoted a lucrative trade to some Asian countries. The practice of shark finning has been illegal in Canada for many years; however, Canada was the largest importer of shark fins outside of Asia until 2019. A grassroots effort led by Oceana Canada led to a law being passed in June of 2019 that banned the import and export of shark fins in Canada – a major win for basking sharks.
Globally, basking sharks have been listed as Endangered by the IUCN Redlist due to global, decreasing population trends and their life history traits that make them vulnerable to human impacts. In Canada, the Atlantic population is a common occurrence in the summer months and they are believed to be a healthy population. The Atlantic population has not been designated by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), nor have they been listed under the Species at Risk Act (SARA). The Pacific population, on the other hand, has been assessed by COSEWIC as Endangered and is listed under schedule 1 of SARA as Endangered. While basking sharks were historically seen in large groups off the coast of British Columbia, directed fishing and eradication efforts made the Pacific population virtually disappear. There are only six confirmed records of basking sharks in the Canadian Pacific since 1996.
