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Sunday Crocodilian - Crocodylus johnstoni Edition

No U.S. Independence Day weekend would be complete without learning about some kind of crocodilian. I am here to fill that void. No need to thank me, I'm only doing my self-appointed job.

The Australian Freshwater Crocodiles (Crocodylus johnstoni) can only be found in the northern freshwater regions of Australia. Locals call these smaller cousins of the saltwater crocodiles "Freshies," although they're also known as Johnston's Crocodile. Gerard Krefft, one of Australia's most prominent zoologists, had intended to name the crocodile after the man who had first reported it to him (Sir Henry Johnston), but made a mistake when he submitted his papers. Officially, the correct scientific name for the species is Crocodylus johnsoni, rather than johnstoni, but most literature has been updated to reflect the intended name.


Relatively speaking, Australian Freshwater Crocodiles are small, with males reaching lengths of almost 10 feet (3 meters) long, and weighing 150 pounds (70 kg). Females are even smaller, growing up to 6.9 feet (2.1 meters) and weighing about 88 pounds (40 kg). Unusually large specimens have been recorded to weigh 220 pounds (100 kg), like the larger recorded individuals living in Lake Argyle and Katherine Gorge.

Australian Freshwater Crocodiles prefer habitats like billabongs, rivers, wetlands, and creeks. In some parts of their range, they compete with saltwater crocodiles, but they can also live where their larger cousins cannot. The Australian states of West Australia, Queensland and the Northern Territory contain most, if not all, of the population of Australian Freshwater Crocodiles.


Fish, crustaceans and insects comprise the bulk of the Australian Freshwater Crocodile's diet, though they will occasionally take small mammals. They are generally not considered to be a threat to humans if they are not provoked, though there have been a few recorded attacks on humans. During the dry season, females will lay their eggs in holes along the riverbank, and the eggs hatch at the beginning of the wet season. Females do not defend their eggs during incubation, but they will scoop the hatchlings up into their mouths to carry them to water, and assist them during the hatching process. A very small percentage of hatchlings make it to adulthood.


In the absence of saltwater crocodiles, Australian Freshwater Crocodiles usually thrive, but recently the population has suffered significant decline due to the existence of an invasive species. Cane Toads are native to Central and South America, but have recently been introduced to Australia and have had a negative impact on the Australian Freshwater Crocodiles. These toads are poisonous to them, though not to saltwater crocs. A harmful parasitic trematode has also contributed to the species' decline.

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