Research
White sharks
The biology of white sharks
White sharks are torpedo-shaped with a pointed snout, large pectoral
and first dorsal fins, a crescent-shaped tail, a large black eye, and
large triangular serrated teeth. They are grey or bronze-coloured on top
and white below.
They differ from most other sharks and scale-fish in that they are
warm-bodied. The temperature of a white shark can be as high as 24-27°C
and as much as 13-14°C above the surrounding water temperature. They
maintain their body temperature using a heat exchange system that retains
the heat generated by their muscles. Being warm-bodied has helped white
sharks to become dominant predators of swift-moving prey in cool and
cold environments.
Age and growth
White sharks grow fairly rapidly at first, (20-30 cm per year in sharks
less than 3.0 m), but their growth is poorly documented after maturity.
Lengths and estimated ages at maturity are 4.5-5.0 m at 12-17 years for
females and 3.6-3.8 m at 7-9 years for males. Females reach larger sizes
than males, growing to probably 6 m and 3000 kg, and may reach 50-60 years
of age. Individual sharks of about 5 m in length are estimated to be 15-25
years old.
Reproduction
Reproduction in white sharks is poorly documented due to the low number
of pregnant females reliably examined. As with all sharks, fertilisation
is internal. Unlike some sharks, there is no placental connection with
the mother. Instead, the embryos feed on unfertilised eggs produced by
the female during pregnancy.
Embryonic developmental rates are unknown and the gestation period may
be as long as 18 months. They are believed to give birth in spring-summer,
probably in many, mostly temperate, locations worldwide.
Reported litter sizes range from 2-17. The pups are 1.2-1.5 m long at
birth and can weigh up to 32 kg. They are born fully formed and there
is no parental care. The sex ratio of litters, when reported, has generally
been close to 1:1.
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Mortality
There have been no direct measures of natural mortality but it is assumed
to be low, based on the species low reproductive potential and top order
predator status.
Diet
The white shark is a versatile predator and feeds on a wide range of
prey including pelagic and demersal finfish, sea turtles, marine mammals
and some invertebrates such as squid and crustaceans. Marine mammals,
where available, appear to become more important in the diet when sharks
reach 3-4 m in length. However even large sharks can rapidly switch between
periods dominated by seal and sea lion predation to different predatory
strategies targeting fish in nearby habitats.
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