Meet the largest of all fish in the St. Lawrence, the basking shark.

Cetorhinus maximus

Basking shark, elephant shark, bone shark, nurse fish, sunfish, sailfish, hoe-mother, squale pèlerin (Fr.), squale géant (Fr.), éléphant de mer (Fr.), poisson à voiles (Fr.)

The basking shark is the second largest shark and fish in the world, and the only member of the Cetorhinidae family. It is found near the coast in northern and temperate waters where it is often observed feeding at the surface. In Eastern Canada, it seasonally ranges from Newfoundland in the north, to the St. Lawrence Estuary in the west.

Despite its huge size, the basking shark poses no threat to humans since it subsists on plankton. It is a filter feeder, relying solely on forward movement and its wide mouth to capture plankton while swimming at a speed of approximately 2 knots (3.7 km/h; 2.3 mph). It is not known where Canadian specimens spend winter although individuals tagged in New England during summer are known to have swum as far south as Brazil¹. A number of historical sources claim that the basking shark hibernates on the sea floor during winter, including in the St. Lawrence. This idea was debunked in 2003 when scientists of the Marine Biological Association (UK) discovered that the basking shark actually feeds on plankton at depths up to 900 m during the cold season².

The North Atlantic population, including individual sharks that make it into the St. Lawrence, is far more numerous than basking shark numbers in the northeast Pacific. Among other explanations, the British Columbia population was nearly hunted to extinction during the mid-twentieth century as it was viewed as a competitor for lucrative fisheries³.

¹ Skomal, Gregory B.; Zeeman, Stephen I.; Chisholm, John H.; Summers, Erin L.; Walsh, Harvey J.; McMahon, Kelton W.; Thorrold, Simon R. 2009. Transequatorial Migrations by Basking Sharks in the Western Atlantic Ocean. Current Biology. 19 (12): 1019–1022.
² Sims, DW; Southall, EJ; Richardson, AJ; Reid, PC; Metcalfe, JD (2003). Seasonal movements and behaviour of basking sharks from archival tagging: no evidence of winter hibernation. Marine Ecology Progress Series. 248: 187–196.
³ Wallace, S., Gisborne, B. 2006. Basking Shark. The Slaughter of BC’s Gentle Giants. New Star Books, 92 p.
Basking shark (Cetorhinus maximus).
Illustration © Jeffrey Gallant | ORS
White shark (Carcharodon carcharias) filmed off Cape Cod (Massachusetts) by the Atlantic White Shark Conservancy in 2017.

Names and Taxonomy

Common Names: basking shark, elephant shark, bone shark, nurse fish, sunfish, sailfish, hoe-mother, squale pèlerin (Fr.), squale géant (Fr.), éléphant de mer (Fr.), poisson à voiles (Fr.).

Order: Lamniformes (mackerel sharks)
Family: Cetorhinidae (basking shark)
Genus: Cetorhinus
Species (scientific name): Cetorhinus maximus* (Linnaeus, 1758)

Cetorhinus: from the Greek words words [ketos] = sea monster, and [rhinos] = nose.
maximus: Latin [great] = great.
*sea monster with a big (great) nose

Size and Appearance

“The first clear and entire view of a basking shark is terrifying. One may speak glibly of fish twenty, thirty, forty feet long, but until one looks down upon a living adult basking shark in clear water, the figures are meaningless and without implication. The bulk appears simply unbelievable. It is not possible to think of what one is looking at as a fish. It is longer than a London bus; it does not have scales like ordinary fish; its movements are gigantic, ponderous, and unfamiliar; it seems a creature from a prehistoric world, of which the first sight is as unexpected, and in some ways as shocking as that of a dinosaur or iguanodon would be.”
— Gavin Maxwell, Harpoon Venture, 1952.
¹ Randall, J. E. 1987. Refutation of lengths of 11.3, 9.0, and 6.4 m. attributed to the white shark, Carcharodon carchariasCalifornia Fish and Game, 73 (3): 163–168, figs 1–3.
² Compagno, L., Dando, M., Fowler, S. 2005. Sharks of the World. Collins, 368 p.
³ Uchida, S. Toda, M., Teshima, K., Yano, K. 1996. Pregnant White Sharks and Full-Term Embryos from Japan. In: Klimley, A.P. & Ainley, D. (Eds.) Great White Sharks. The biology of Carcharodon carcharias: 139–155.

Dentition

Although it is exclusively a filter feeder, the Basking shark has hundreds of little teeth in it upper and lower jaws. The teeth are so small that they are not apparent unless observed from a short distance on a carcass. The teeth may assist gestating basking shark embryos to feed on the mother’s unfertilized ova (oophagy) before switching to filter feeding after birth¹.

¹ Martin, R. Aidan. Biology of the Basking Shark (Cetorhinus maximus). ReefQuest Centre for Shark Research.

Distribution

¹ Gore, M. A., Rowat, D., Hall, J., Gell, F. R., & Ormond, R. F. 2008. Transatlantic migration and deep mid-ocean diving by basking shark. Biology letters4(4), 395–398.
Basking shark postage stamp released by Canada Post in 2018.

Provisional distribution of the basking shark (Cetorhinus maximus) based on research by the St. Lawrence Shark Observatory (ORS). This map is updated with new and historical data on an ongoing basis. To submit additional sightings or captures, please contact us. Click on shark icons for observation details. Note: Map works best in full-screen mode.

Prey

The basking shark mostly feeds on plankton consisting of small fish and invertebrates. It can filter up to 2,000 short tons (1,800 t) of water per hour, relying solely on the passive flow of water going through its pharynx as it swims at a speed of approximately 2 knots (3.7 km/h; 2.3 mph).

The plankton-laden water enters the shark's wide open mouth where it is strained by gill rakers located in the gill slits.

Reproduction

Basking sharks are ovoviviparous. Embryos feed on a yolk sac and later on unfertilized ova (oophagy), possibly utilizing their teeth which are no longer useful after the shark has switched to filter feeding¹. Gestation is believed to last up to three years. Pups are born fully developed at 1.5 - 2 metres (4.9 - 6.6 ft). Litter size is approximately 6 pups (only one pregnant female has ever been captured) every 2 to 4 years. Mating and birthing are thought to occur in shallow water in the summer.

¹ Martin, R. Aidan. Biology of the Basking Shark (Cetorhinus maximus). ReefQuest Centre for Shark Research.

Life Expectancy

The lifespan of the basking shark may reach up to 50 years¹.

¹ Canadian Shark Research Lab - Fisheries and Oceans Canada (DFO)

Attacks

No deliberate attacks on humans have been attributed to the basking shark. Most known incidents have involved humans getting too close and getting hit by the caudal fin (tail), or coming into contact with the basking shark's skin. The skin is covered with large dermal denticles that have on occasion inflicted injury on divers and scientists¹.

¹ Florida Museum of Natural History. Discover Sharks - Cetorhinus maximus.

Fisheries

The basking shark is not hunted in Canada or the U.S. and many directed fisheries in the world have closed. A few fisheries still exist in Asian markets where the basking shark is hunted for its liver oil, meat, cartilage and fins. Large numbers are also caught as by-catch and for the illegal fin trade.

The basking shark was deliberately hunted to near-extinction by government patrol vessels and fishers in British Columbia the during the mid-twentieth century as it was viewed as a competitor for lucrative fisheries.

"This year, starting a fortnight before the season opens, it is planned to send a punitive expedition against the sharks. It will be manned by men with rifles, and it will have boats with steel-shod bows and good speed. These boats will ram and slash the sharks. Death may come then to the sharks so attacked. The blood of the slaughtered sharks is expected to drive others away as it has done in the past."
— The Province, February 3, 1943, p. 25.

Status

The Atlantic population of the basking shark is listed as a special concern species by COSEWIC (Committee on the Status of Endangered Wildlife in Canada).