|Photo modified from
Sharks, History and Biology of the Lords of the Sea. A. Mojetta. 1997.
Swan Hill Press.
The blue shark is one of
the most easily recognized sharks. It has a distinct colouration, a deep indigo
blue from above and a vibrant blue on its sides, changing to white underneath.
The large pectoral fins are also easy to spot as they are as long as the
distance between the tip of the snout to the last gill slit. The blue shark is
a long slender shark, reaching 3.8 meters (13 feet) in length. It is likely the
most prolific of the large shark species as it is abundant throughout its
range. The blue shark has a weak keel on the caudal peduncle and the upper lobe
of the caudal fin is larger than the lower. The teeth on both the lower and
upper jaw have triangular cusps with smooth or finely serrated
The diet of this shark
includes many types of fish and squid, and may sometimes eat seals. Although
flatfishes make up part of the diet, blue sharks predominantly eat pelagic
fishes such as herring, silver hake, white hake, red hake, cod, haddock,
pollock, mackerel, butterfish , sea raven, tuna and swordfish. Fish caught on
longlines during fishing are often attacked and consumed by blue sharks, who in
turn often become ensnared in the fishing gear.
The blue shark is a
viviparous species, nourishing the young in the uterus and giving birth to live
pups. The new-born pups measure 40 to 51 cm (16 to 20 inches) in length and
litters usually consist of between 25 to 50 individuals. Litters of up to 135
pups have been reported. Females reach sexual maturity at a size of 2.2 to 3.2
meters (7 to 11 feet), while for males it is achieved at lengths of 1.8 to 2.8
meters (6 to 9 feet). After copulation the females may retain and nourish the
spermatozoa in the oviducal gland for months or even years while she awaits
ovulation. Once the eggs have been fertilized there is a gestation period of
between 9 and 12 months.
In temperate waters the
blue shark is a wide ranging pelagic species occurring near the surface. In
tropical waters the blue shark is more commonly found in deeper waters as it
prefers temperatures between 7 and 16 degrees Celsius.
The blue shark occurs in
the Atlantic, Pacific and Indian Oceans in both inshore and offshore waters.
This wide ranging species is found from 50º N latitude to 50ºS
latitude. In the western Atlantic it can be found from Newfoundland and the
Gulf of St. Lawrence to Argentina. In Canadian waters the blue shark has been
found in southeastern Newfoundland, the Grand Banks, the Gulf of St. Lawrence,
the Scotian Shelf and the Bay of Fundy.
- Long slender body
- Dark blue colour on top, bright blue
colour on the sides and white underneath
- Very long pectoral fins
- Nictitating membrane over eye