A basking shark (Cetorhinus maximus),
the second largest and highly endangered shark species.
© J. Stafford-Deitsch
Many biological aspects of the basking sharks are still a complete mystery. We do not
know where the animals spend the cold season, and their gill rakers - a shedable
filter structure in their mouths designed to strain plankton from the water - is a puzzle
The basking shark's most important characteristics are its long gill slits which almost
encircle the head and its pointed snout. Additional recognizable features are its lunate
caudal fin and well-formed lateral keels.
The maximum size of these animals is approximately 10 meters. Reports on larger
specimans have to date not been confirmed. Their maximum age is unknown,
although efforts are being made to determine this by counting the number of vertebral
spines/Wirbelringe (similar to the growth of tree trunks) and comparing them to the
size of animals in known populations.
Basking sharks belong to the few plankton eaters in the shark world. The only other
filter-feeding species known to prefer plankton are whale sharks
Fact Sheet Shark Info 3/00) and megamouth sharks
(Megachasma pelagios, Fact
Sheet Shark Info 1/99). Although other species such as the blue sharks (Prionace
glauca) also have the necessary filter structure in the gill region which allows them to
strain water and thus feed on plankton (krill) as their basic food, they only do this in
rare cases. Called gill rakers, they are the main reason why basking sharks swim
through the water almost permanently with wide open mouths. Compared to whale
sharks, basking sharks are passive filterers, meaning they do not actively suck in
water but rather let it flow in while swimming.
This species' method of reproduction has not been widely researched. As with other
representatives of the same group (white sharks, mackerel sharks, thresher sharks,
etc.), they too bear living young, but the embryos are not connected by placenta to the
mother (aplacental viviparous or ovoviviparous). The embryos nourish themselves by
feeding on eggs produced by the mother (oophagy, the eating of eggs). Their size at
birth is approximately 1.7 meters long. Based on counts made of the number of
animals and their sex, the species appears to mate in schools prevailed by females. In
addition they seem to have the longest gestation period of all sharks.
This species prefers cool and temperate waters and is distributed almost worldwide,
although they appear to be limited to regions on the continental shelf. They are seen
both in immediate proximity to the shore as well as in open waters. They also appear
to be migratory, periodically appearing in certain places. Basking sharks can be found
on the northern hemisphere off the coast of China, Korea and around Japan, on the
East coast of the U.S., from Newfoundland down to Florida, around Great Britain and
Norway, but also in the Mediterranean. In the southern hemisphere they are found
primarily in Southern Australia, parts of South America and the tip of South Africa.
Basking sharks migrate mostly in schools, accordingly they also feed together. Their
feeding behavior and migrations appear to be connected with the blooming of
plankton. One theory is that when no plankton is available the animals periodically
retreat to deeper regions where they shed their gill rakers. Based on this hypothesis
the gill rakers are then regenerated by the time the next plankton blooms. Thanks to
deposits of fat in their huge liver, they have no problem in overcoming this time period
without plankton. Other theories say the animals who have shed their gill rakers do
not fast when no plankton is available, but revert to feeding on organisms living on the
ocean floor. More research will be necessary before these behavioral patterns are
Basking sharks are harmless. Years ago the animals were hunted for their huge liver
with its high content of Vitamin A and oil, the latter of which was used as lamp oil.
Because of their very low reproduction rates and the strong pressure put on their
populations by the fishing industry, these animals are today found on the IUCN list of
endangered shark species.
Basking sharks were the basis for many sea monster reports. They have a habit of
swimming directly underneath the surface of the water ("basking" means to sun
oneself or bask in the sun) and are frequently observed swimming in a row so that
their dorsal fins and the upper lobes of their caudal fins penetrate the water, giving the
impression that it is one huge animal.
May be published only by indicating the source: Shark Info / Dr. Erich K. Ritter