Name
The Saltwater crocodile, crocodilus porosus, is also known as the
estuarine crocodile. The term porsus comes from the Greek porosis
meaning full of calloses and refers to the bumpy nature of the upper
surfaces of the body. The word crocodile originates from Greek krokodilos
meaning “worm of the stones”, referring to their habit
of basking on pebbles at the waters’ edge. In Australia the
species is commonly refered to as ‘Salties’. Distibution
There are thirteen subspecies of the genus crocodylidae, two of
which, the freshwater and the saltwater, are found in Australia.
Crocodilus porosus is found around south east Asia from India to
Australia. In Australia it is found from south-east Queensland around
the top-end to north-east WA. It frequents coastal waters, rivers
and billabongs (ox-bow lakes) up to 200km inland and have been known
to travel 1000km by sea.
Description
At up to 7 metres in length and one tonne in mass, it is the largest
extant example of the species and the largest surviving reptile
in terms of mass. However, specimens over 5 metres long are very
rare and at their average length the weight will be closer to 500Kg.
Females are smaller, generally reaching a maximum length of 3 metres.
Young salties have a pale yellow colouration with dark spots and
stripes. After many years they become darker with lighter areas
visible, the underside being a creamy white. Colouration does, however,
vary with area. They have a pair of ridges running from the eyes
to the snout which become more distinct with age and have oval shaped
scales
Thay have particularly large heads and strong jaws (strong enough
to crush a buffalo skull) and the ears, nose and eyes are all on
the top of the head, allowing these senses to be used whilst almost
completely submerged. The eyes have a nictitating membrane which
act as a second, clear, set of eyelids, giving protected underwater
vision.
Crocodiles spend most of the time basking in order to regulate body
temperature (at 30 to 32 degrees C) and defending a territory by
the use of postures and low-frequency vocalizations. Fights are
rare.
Maximum lifespan is at least 70 years, possibly over 100.
Diet
Saltwater crocodiles are carnivores whose choice of meat depends
purely upon the size of the prey that they are able to catch. Hence
fully grown adults can take prey the size of a buffalo and smaller,
young crocs will prey mainly on crabs and other small crustaceans,
as well as small fish and insects. Large salties will also take
humans, although this is very rare (14 deaths in 27 years since
protection was introduced) and usually due to a lack of care by
the human.
Attack is normally from the waters’ edge and is extremely
rapid. Prey is then normally dragged back to the water where it
is drowned, although when multiple crocodiles are involved death
may be by dismemberment. Larger prey will be torn to small pieces
before swallowing above water to avoid ingestion of large amounts
of water. Hunting is normally at night.
Stones and pebbles are often ingested to aid with digestion and
for ballast.
Reproduction
Female salties reach maturity at 12-14 years old, males a couple
of years later. Reproduction occurs annually. Mating takes place
in September/October, after which a nest will be constructed close
to water (so that the female can remain attentive and still feed).
The nest is a mound of plant material and mud and serves the purpose
of incubating the 40-60 eggs that are laid. The sex of the offspring
is determined by the temperature at which the eggs are kept, 31.6
degrees C produces mainly males, slightly above and below that produces
females. Above 34 degrees all the eggs will die.
Eggs hatch after 80 days and at this time the offspring are no more
than 29cm long. When the first eggs hatch the young produce a characteristic
yelping sound. This leads to the mother digging out the eggs, gently
breaking open the un-hatched eggs, and carrying the young to the
water in her mouth. The young will be raised in fresh water.
Approximately 80% of the eggs will be lost before hatching as a
result of being submerged by rising water, being eaten by goannas
or feral pigs or by being trampled on by buffalo. Once hatched most
of the hatchlings will be taken by fish, birds and turtles and by
non-parental adult crocodiles. Normally less than 1% of the hatchlings
will reach maturity, meaning that only one newborn will survive
every 2 or 3 years.
Conservation
Legal hunting of saltwater crocodiles was stopped in the early 1970’s
in Australia due to the near complete collapse of the population
and as a consequence numbers have increased dramatically. It is
thought that the population is around 100,000 to 150,000 and this
population is regarded as secure. Limited numbers of crocodiles
can be legally taken by indigenous Australians. There is talk of
introducing “safari-style” hunting of crocodiles but
so far this has been resisted.
Crocodiles suffer from their image as ‘man-eaters’ and
there is concern from some quarters that there are now too many
crocodiles. For this reason care needs to be taken not to allow
the return of widespread hunting.
References
http://http://kingsnake.com/oz/crocs/porosus.htm
http://wikipedia.com
http://thebigzoo.com
http://angelfire.com
http://flmnh.ufl.edu/cnhc/csp_cpor.htm the crocodilian species list
Wilson and Swan,
The Complete Guide to Reptiles of Australia
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