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Basking Shark
Cetorhinus maximus
Please send us any new or old sightings of basking sharks
from anywhere in the Pacific.
The basking shark 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. The
basking shark gathers 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. 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. Two PWLF
Directors Jim Darling and Kate Keogh identified 27
individuals in Clayquot Sound in June, July and August 1992
but by 1994, the sharks were gone (Darling and Keogh 1994).
There was a sighting from BC waters was in the Queen
Charlottes Islands in July 2005 (Wallace and Gisborne 2006)
and in Nootka Sound in June 2009. We would like to hear
about any other sightings.
Basking Shark
Video
Have you seen this shark?
Basking Shark
Identification Guide
Basking Shark Distribution and Migration
The basking
shark is reported from coastlines throughout much of the
temperate oceans in both hemispheres of the world. It is also
reported from Hawaii and likely occurs in much of the north
Pacific.
Basking Shark Behaviour, Biology and Conservation
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
have been fished for meat, fins, liver oil, and cartilage (Compagno
2001, Hoelzel 2001) and shot as pests to fishermen’s nets
(Wallace and Gisborne 2006). 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. It also has 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. The
IUCN considers the species to be vulnerable worldwide (IUCN
2004, Fowler 2000), and it became an Appendix II of
the Convention on International Trade in Endangered Species
(CITES). There are few data on regional abundance although the
species was numerous on California and British Columbia
(Squire 1992, Wallace and Gisborne 2006). The Committee on the
Status of Endangered Wildlife in Canada designated the species
endangered in 2007 because of its vulnerability to fishing and
entanglement in fishing gear. There are only six confirmed
sightings on Canada’s Pacific coast since 1996. The minimum
historical population was about 750 sharks compared to near
zero now (COSEWIC
2007).
Please
send us any new or old sightings of basking sharks from
anywhere in the Pacific.
Science
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.
June 2010
Basking Sharks: The Slaughter
of B.C.'s Gentle Giants
by Scott Wallace and
Brian Gisborne
The basking shark is the
second-largest fish in the world, at up to five ton in weight
and 15 metres in length. Once abundant on the British
Columbia coast, they are nearly extinct today after the
federal government began their extirpation from the coast in
the 1950s, because their habit of basking on the surface often
entangled them in fishing gear. Now B.C. produces perhaps one
sighting a year, yet they still have no protection.
Basking Sharks: The Slaughter of B.C.'s Gentle Giants by
Scott Wallace and Brian Gisborne
documents the brutal demise of this plankton-eating behemoth,
and asks if we've learned anything from our disregard for the
ocean's ecosystems. Read more about this book at
http://thetyee.ca/Books/2006/12/07/BaskingSharks/
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