Slender, agile and skilled in the hunt, the
Blue Shark is the epitome of the pelagic predator - one of the most divine and
glorious creatures to grace the oceans of our blue planet.
Reaching
lengths of 3.8 metres and attaining weights of up to 200 kilograms, Blue Sharks
are one of the larger species in the requiem shark family. As is evident, their
name derives from the magnificent indigo pigmentation on their backs, which
fades into a white on its underbelly as camouflage from above and below.
Blue
Sharks are easily identifiable by their large, round eyes and distinctive,
streamlined or cigar-shaped figure. It possesses an elongated snout, at the end
of which are the usual five gill-slits found in more recently evolved shark
species. Beneath these are a pair of long, pointed pectoral fins, which, as
with the rest of the shark's body, are white on the underside and indigo-blue
on top. Unlike many sharks, the dorsal fin of the Blue Shark is closer to its
pelvic fins than to the pectoral fins. An anterior, or second, dorsal fin is
situated close to the tail, or caudal fin. This same caudal fin has a longer
dorsal, or upper, lobe than ventral, or lower, lobe, the former accounting for
up to a quarter of the shark's body length. An anal fin is present on the
underbelly, between the pelvic fins and caudal fin. As with all requiem sharks,
nictitating, or inner, eyelids distinguish them from the family of mackerel
sharks. These tough membranes close over the eyes during the last few seconds
of a hunt or attack, shielding the eye from any damage its prey might attempt to
inflict upon it.
As
an ocean-dwelling, pelagic shark species, Blue Sharks are generally only found
in open water, where they are a frequent menace to anglers and
long-line-fishermen, stealing fish from their lines in an opportunistic
fashion. Blues only inhabit waters between the temperatures of ten and twenty
degrees Celsius, so despite being found in all of Earth's oceans - with the
exception of the Southern and Arctic Oceans - and many of its warmer Seas, such
as the Mediterranean Sea, Caribbean Sea and the Gulfs of Mexico and California,
specimens tend to remain at depths of around 400 metres. Only in colder parts
of the Global Ocean, such as the North Atlantic, the North Sea and the North
Pacific, can they be found closer to the surface. Atlantic Blue Sharks
undertake vast, trans-Atlantic migrations with great frequency, following the
Gulf Stream from the United States of America to the United Kingdom, the Canary
Current from the United Kingdom to West Africa and the North Equatorial Current
from West Africa to the Caribbean and back on to the United States. Some sharks
have been known to deviate from this common course, using the North Atlantic
Drift and the Labrador Current to circle from the United Kingdom to Iceland and
back to the United States. Blues in other areas, such as the Indian and Pacific
Oceans, make similar migrations in their own waters. During this time, the
sharks remain in small, single-sex schools, with larger specimens dominant over
smaller and younger Blues.
Provided
the evade death at the hands of human hunters and at the jaws of larger
predatory animals, Blue Sharks can live for up to 20 years, reaching sexual
maturity at around 6 years of age. Blue Shark mating takes places in the open
ocean and at great depths, meaning marine biologists know little about its
course. It is believed, however, that male sharks will bite females as an act
of courtship, inflicting little damage due to the thickness of the female
sharks' skin - three times that of a male's.
Following
mating, a gestation period of roughly one year takes place before the female
gives birth to a litter of pups numbering from 4 to 135. These young sharks
spend the first few years of their life closer to shore, undertaking migrations
at later ages.
As
with the majority of pelagic sharks, Blue Sharks are scavengers and
opportunists - consuming fish from lines and nets as well as human refuse left
in the sea. Whale, porpoise and dolphin carcasses attract large numbers of
Blues as well as other species of sharks and fish. Occasionally, large
congregations of Blues will go into the infamous feeding-frenzy in competition
over such an opportunity. Large schools of mating squid and of schooling
mackerel can also send specimens into a similar state, although for the most
part the sharks will work together to herd prey towards the surface before
attacking. Should a Blue Shark come across a large food source, it will feed
incessantly - ejecting previously consumed food through the mouth in order to
continue feeding. This trait is not endemic to Blue Sharks, although it is best
observed in them.
To
the sadness of biologists and conservationists alike, Blue Sharks,once the most
abundant shark species, are drawing closer to classification as an endangered
species. An estimated 20,000,000 Blue Sharks are caught and killed each year,
primarily for the shark-fin soup industry in Eastern Asia. Drift nets and
trawler nets also pose terrible threats not only to Blue Sharks but to all
pelagic marine life, and it is these nets which are targeted for illegality by
conservation groups such as SharkTrustUK and Shark Savers in America. As Blue
Shark numbers decrease, it is humanity's duty to act now, and save our beloved
marine ecosystem from the brink of extinction.
Bibliography
Jonathan
Bird's Blue World, Season One, Episode One, Blue Shark Adventure
Page
183, The Nature Company Guides; Sharks & Rays, The Nature Company
Guides, Time-Life Books, 1997
Page
93, The Nature Company Guides; Sharks & Rays, The Nature Company
Guides, Time-Life Books, 1997
Page
15, A Very Short Introduction: Marine Biology, Philip B. Mladenov,
Oxford University Press, 2013
Page
24 - 25, Encyclopaedia of Sharks, Sally Morgan, Igloo Books Ltd, 2010
Daniel Bailey
Sunday 7th of February 2016, 14:19 GMT
England
Dedicated to Ron and Valerie Taylor - my inspiration.
