Crocodiles first walked this earth 250 million years ago during
at the Age of the Dinosaurs.
Since this time many species of crocodiles have evolved.
Today in the Top End of Australia there two species:
the Estuarine Crocodile (Crocodylus porosus) and the Freshwater
Crocodile (Crocodylus johnstoni).
The Estuarine Crocodile is the largest living reptile.
Also known as the Saltwater Crocodile, these great survivors of
the dinosaur age have been known to grow up to 7 metres in length.
The "Saltie" inhabits coastal and freshwater rivers,
billabongs, floodplains and the open sea.
It is considered to be the Top End's most dangerous predator.
Hunting during the post World War II era (1945+) had a drastic
effect on the population size.
In 1971 the Saltwater Crocodile became a protected species in the
Northern Territory.
Since then their numbers have increased steadily.
Saltwater Crocodiles are found mainly in coastal areas, swamps
and inland rivers.
They live in both fresh and salt water.
Freshwater Crocodiles live only in fresh water.
When swimming the tail is the main means by which the crocodile
moves.
The raised scutes increase the area of the tail and are important
in thermo-resolution.
Like all reptiles, the crocodile's body is protected by scales.
Scales on the back are very thick and help protect the crocodiles
in fights.
Within each of these scales bone can be deposited giving the scales
a raised appearance.
Scales on the stomach are much thinner.
Most reptiles have a three-chambered heart.
However, like humans, crocodiles have a four-chambered heart.
This allows them to divert oxygen to the brain so that they can
stay underwater for long periods when they dive.
Eyes and nostrils are mounted on top of the crocodiles head which
allows it to submerge almost completely while still being able
to see and breathe.
Binocular vision allows the position of the pray to be judged accurately.
A well developed sense of hearing helps locate and track pray.
The palatal valve at the back of the throat prevents water from
flowing into the crocodile's stomach and lungs.
When basking, the palatal valve is opened but when in the water
or holding prey in its mouth, the valve is closed and breathing
is done through the nostrils.
Crocodile jaws are extremely powerful and are designed to trap
and crush prey.
The teeth interlock perfectly which helps in the capture and holding
of prey.
Crocodiles regulate their body temperature by external means.
The ideal temperature for a crocodile is between 30°C and 33°C.
To keep within this range it has to "warm up" by basking
in the, sun, and "cool down" by seeking shady cooler
areas.
The inside of a crocodile's mouth is well supplied with blood vessels
which, when basking with the mouth open, help in heat exchange
and cool the brain.
Females begin nesting at the beginning of the wet season (October-March)
with the construction of their nests.
The nests are mounds of mud, reeds and grasses.
About 50 eggs are laid and buried just beneath the surface.
The female stays on guard near the nest until they hatch.
The natural heat and humidity incubate the eggs which hatch after
about two months.
It is the temperature of the nest which determines the sex of the
baby crocodiles.
At 30°C females will develop, at 31°C both males and females
will develop and at 32°C - 33°C they will be mostly males.
Very few eggs survive to maturity.
Flooding destroys many of the eggs and the hatchlings make a good
meal for many predators.
If they can survive the first few years of life there is a good
chance that they will reach maturity.
For females this occurs at around 12 years and 2.3 metres in length;
for males it is around 16 years and 3.3 metres.
A Saltwater Crocodile's diet depends on its age and size.
Young crocodiles prefer insects, crustaceans, small turtles, fish
and small rodents.
As the crocodile grows so does the size of its prey.
Mature crocodiles feed on smaller crocodiles, kangaroos, waterfowl,
feral pigs, mud crabs; turtles, snakes, rodents, fish, goannas,
flying foxes, wallabies, dingoes, dogs, feral cats and occasionally
humans.
Generally crocodiles stalk their prey from the water.
They lie with just their eyes and nostrils above the water.
The attack is sudden and deadly.
Powerful jaws crush the prey and the crocodile rolls quickly under
the water until the prey is dead or stops moving.
Crocodile farming
There is a growing world market for crocodile products.
Several crocodile farms in the Top End are open to tourists and
display crocodiles in captivity.
Because mortality is so high in the first year crocodile eggs can
be collected from the wild without affecting population numbers.
Eggs are incubated and a high percentage hatch successfully.
Young crocodiles are raised in crocodile farms for their meat and
skins.
Problem crocodiles that threaten humans are caught and sent to
one of the crocodile farms.
Large ones join the captive breeding program.
Crocodile hunting
Crocodiles were hunted by Aboriginal people for thousands of years
and later by early settlers.
In the mid - 1940s a market for skin exports developed and as a
result hunting during the 1940s and 1950s was intense.
Population numbers were greatly reduced.
By the 1960s crocodiles were becoming hard to find.
Few hunters were making an income and many recognised that crocodile
populations had reached a critically low level.
In 1971 the Northern Territory Government banned the hunting of
crocodiles and today the number of animals is increasing rapidly.
Crocodiles were skinned by cutting along the spine so that the
valuable belly skin was kept intact.
The catch is lined up on the beach ready for skinning.
The skins were the only valuable parts the meat was not usually
used.
Skins were salted and spread out to dry in the sun.
Even small crocodiles produced useful skins.
Crocodile trapping
Crocodiles are a danger to humans so they are removed from areas
near human habitation.
Small crocodiles, up to 1.2 metres, are caught by hand or net.
This is a dangerous business as even small crocodiles can give
a severe bite.
Larger crocodiles, from 1 to 5 metres in length, are caught with
harpoons.
The harpoon is stuck into the neck, or tail of a crocodile and
it is then pulled to the side of the boat.
Crocodiles that are too wary or too large to be caught by harpoons
are caught in traps baited with meat.
Some traps have sensors which signal when a crocodile has been
trapped.
Safety
Saltwater Crocodiles are very dangerous animals and close attention
should be paid to safety when in areas where they are found.
Swimming, wading, or bathing in crocodile inhabited waters is dangerous.
Look out for signs that warn you of areas that are not safe to
swim in, or check with rangers before you enter the water.
When fishing stand on the banks or fish from a boat.
Avoid standing in the water.
Do not clean fish near the water's edge; use the bins provided.
Drinking at the water's edge should also be avoided. '
Do not camp too close to the water's edge. |
