The basking shark (Cetorhinus maximus) is the world’s second-largest fish next to the whale shark (Rhincodon typus). Both species are gentle, slow-moving plankton-feeding creatures.
The basking shark is found throughout much of the temperate oceans in both hemispheres of the world. They gather in large numbers where there is an abundance of plankton.
Some individuals are 14 meters long and weigh up to 7 tonnes. Males reach an average of 9 meters, females 9.8 meters. It is usually greyish-brown, with mottled skin. The caudal fin has a strong lateral keel and a crescent shape. Other common names for it include bone shark, elephant shark, sailfish, and sunfish.
Basking Shark Habitat And Conservation
Between seasons, basking sharks will travel hundreds of kilometers. The species was numerous in California from October to May (Squire 1990) and off the British Columbia and Alaska coast in summer suggesting a seasonal coastal migration. The species was very numerous along the west coast of Canada including in inshore waters of the Strait of Georgia until very recently.
Wallace and Gisborne (2006) reported that basking sharks were routinely hunted by the Department of Fisheries and Oceans in the 1950s and 1960s when at least 403 animals were killed along the west coast of Vancouver Island. The sharks were a nuisance to fishermen when they became entangled in nets. The economic hardship prompted the actions to rid the waters of the sharks.
Wallace and Grisborne (2006) describe how the sharks were killed using a knife blade attached to the bow of a boat. The actual number killed is not known but it seems to have been sufficient to lead to the disappearance of the sharks from these waters. Attitudes changed and a few basking sharks appear periodically in BC waters.
Basking Shark Behavior
Basking sharks feed exclusively by straining plankton from seawater passed through gill rakers in their wide mouths while swimming very slowly just below the surface. The slow-moving dorsal fin is diagnostic of this animal.
Very little is known about its biology. The few studies indicate a skewed sex ratio in which females far outnumber males. Basking sharks are thought to mate first at about 12-16 years of age.
Mating occurs in early summer and females give birth to 2-3 pups 1 to 3 years later. They then rest for 2-3 years before mating again. The maximum age is thought to be about 50 years (Kunzlick 1988, Matthews 1950, Parker and Stott 1965).
Basking sharks require 16–20 years to reach sexual maturity. Females have the longest gestation period of any vertebrate at between 2-3 years long after which they give birth to 2-6 pups.
They also have a very low genetic diversity likely resulting from a population bottleneck in the Holocene (Hoelzel et al. 2006). Late maturation, slow reproductive rate, and small number of offspring are characteristics that make this species especially vulnerable to exploitation.
References:
- Compagno, L., 2001. Sharks of the World: an annotated and illustrated catalogue of the shark species known to date. Vol. 2. Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Rome: FAO.
- Darling, J. D. and K. E. Keogh. 1994. Observations of basking sharks, Cetorhinus maximus, in Clayoquot Sound, British Columbia. Canadian Field-Naturalist 108:199-210.
- Fowler, S.L. 2000. Cetorhinus maximus (North Pacific subpopulation). 2006 IUCN Red List of Threatened Species.
- Hoelzel, A. R. 2001 Shark fishing in fin soup. Conservation Genetics 2: 69–72.
- Hoelzel, A.R., S. M. Shivji, J. Magnussen and M. P. Francis. 2006. Low worldwide genetic diversity in the basking shark (Cetorhinus maximus). Biological Letters 1059:1-4.
- Kunzlik, P.A. 1988. The basking shark. Scottish Fisheries Information Pamphlet No. 14. Department of Agriculture and Fisheries for Scotland. Aberdeen.
- Mathews, L.H. and HW Parker. 1950. Notes on the anatomy and biology of the Basking Shark. Proc. Zool. Soc. Lond. 120 (3): 356-357
- Parker, H.W. and FC Stott. 1965. Age, size and vertebral calcification in the Basking Shark Cetorhinus maximus (Gunnerus). Zoological Mededelingen 40 (34): 305-319
- Squire, J.L. 1967. Observations of Basking Shark and great White in Monterey Bay 1948-1950. Copeia 1:247-250
- Squire, J.L. 1990. Distribution and apparent abundance of the Basking Shark Cetorhinus maximus off the central and southern California coast 1962-1985. Marine Fisheries Review 52: 8-11.
- Wallace, S. and B. Gisborne. 2006. Basking sharks: the slaughter of BC’s gentle giants. Transmontanus/New Star Books, Vancouver.