Habitat
Open-sea.
Geographical spread
Entire temperate and colder north Atlantic, in the east from N Africa to
Iceland and northern Norway and in the western Mediterranean as well. In northern regions
they are only found in summer, in winter they withdraw to greater depths.
Current population
Very little is known about numbers around the British Isles or indeed
elsewhere.
Status
IUCN previously classified this species as threatened but there is insufficiently known
about them. In 1996 their status has been upgraded to vulnerable by the IUCN and they are
considered locally threatened. They are only protected around the Isle of Man.
Size
Length of at least 12m.
Weight
About 4 tons.
Average life expectancy
Not fully sure, closest estimate is 10-20 years (Marine Conservation
Society).
Normal diet
Filter-feeder. Cruises (at about 4km/hour) with mouth open and passively strains
small crustaceans (shrimp-like copepods, especially Calanus) from the water. It also ingests
other things floating in the water such as eggs and larvae of fish, squid and other similar
organisms. Filters 1000-1500 tons of water through its gills per hour.
Normal lifestyle
Sometimes solitary, sometimes seen in 'schools' of 50-250 individuals.
Between Aprila and September plankton is abundant in the North Atlantic and the sharks 'bask'
at the surface. The gestation time is thought to be more than 3 years. Female Basking sharks
give birth to 1 or 2 live young that are 1.5m long at birth. Sexual maturity is reached at 3-4 years
of age. In September they disappear and withdraw to deeper depths where the gill filter system
disintegrates and it is presumed that they do not feed and probably hibernate. Very little is
known about what happens to the Basking sharks during the winter months.
Previous geographical spread
Population wiped out in mid-1970s from Achill Island on the
west coast of Ireland. At the height of the kill 11,000 basking sharks were killed in one year. The
population began to decline in the 1950s dropping to less than a thousand fish.
Reasons for decline Historically and today the Basking shark is hunted for its liver, which is
large as in most sharks. From the liver, an oil rich in squalene is extracted. This oil is used in
the cosmetics industry and also as a lubricant for high-flying aircraft. During WWII the Japanese
Mitsubishi J2M Raider fighters used lubricant made from the liver oil of Basking sharks. The
cosmetics industry also requires squalene-rich oil which is used in skin protectors and
softeners. Although there are substitutes which can be extracted from seeds, Estee Lauder in
New York claim they are not as effective or safe as squalene. The Japanese believe that
squalene helps protect against cancer and heart attacks and sells it as 'marine gold' for a dollar
a pill.
Basking shark carcasses are not wasted, the meat is used for domestic consumption (steaks,
fishburgers), or for bait in crab and lobster pots.
The trade in shark fins is increasing all the time and poses a severe threat to Basking shark
numbers. Shark fins are worth $45-50/kilo.
Current threats
Norwegian whale-catchers are the main exploiters of Basking sharks, taking
800-1,000/year in British waters. Portugal comes a close second and there is now competition
from Spanish fishermen. The main problem lies in the fact that the majority of sharks caught
are female which can lead to too few breeding females.
Conservation projects
In 1986 the Marine Conservation Society (MCS) started a tagging
programme and a 'Basking Shark Watch' which was aimed at gaining a greater understanding
of the Basking sharks biology. This project is still continuing today and the MCS has a large
network of volunteers who record sightings and information on Basking sharks. The MCS is also
campaigning to have the Basking shark protected under the Wildlife and Countryside Act. They
have put forward proposals for the last 2 years and have compiled a strong case for 1996
review. 6 other British organisations and scientists have also put forward proposals this year
(1996) to grant proctected status to this species.
File last modified Thursday, October 3, 1996