Freshwater Crocodile information

The Freshwater crocodile, Crocodylus johnstoni, is a crocodile endemic to northern Australia. Compared to the other Australian crocodile, the Saltwater crocodile, the Freshwater crocodile is a small crocodilian that does not pose a threat to humans.    

Freshwater Crocodile taxonomy

Kingdom:      Animalia
Phylum:         Chordata
Class:            Sauropsida
Order:           Crocodilia
Family:          Crocodylidae
Subfamily:    Crocodylinae
Genus:           Crocodylus
Species:         Crocodylusjohnstoni

Freshwater Crocodile conservation status

Crocodylusjohnstoni is listed as Least Concern on the IUCN Red List of Threatened Species.

The estimated wild population is comprised of 50,000-100,000 individuals.

The major threat to this species is habitat destruction. Poaching do occur but is not very widespread. During recent years the population has suffered from the invasive Cane Toad (Bufo marinus). Freshwater crocodiles that ingest Cane toads can die of the toxin. (Interestingly enough, Saltwater crocodiles do not seem to have a problem with eating Cane toads.) However, only the pygmy populations are believed to be under any long-term threat from these toads.

Freshwater Crocodile range

The Freshwater crocodile is native to the Australian states Western Australia, Queensland, and the Northern Territory.

Freshwater Crocodile habitat

Freshwater crocodiles are chiefly found in freshwater billabongs, wetlands and upstream rivers and creeks. This species tolerates saltwater but competes poorly with the larger Saltwater crocodile. It is common in environments where the Saltwater crocodile can not survive, such as very arid inland habitats, rocky environments and high elevations. It can however be found sharing habitat with Saltwater crocs in quite a few spots, e.g. in low-level billabongs.  

During the period when the Saltwater crocodile was extensively hunted for its hide, the Freshwater crocodile expanded its range to include more saline areas where the Saltwater populations had been depleted. This trend has now been reversed by the recovery of the Saltwater crocs.

Freshwater Crocodile size and appearance

The Freshwater crocodile is a fairly small species where the males grows no bigger than 2.5-3 meters (9.8 feet) and the females generally stay smaller than 2.1 meters (6.9 feet). It normally takes at least 30 years for a male to reach a length of 2.5-3 meters (9.8 feet).

The Freshwater crocodile is light brown with darker bands on body and tail; bands which break up near the neck on many specimens. The body scales are comparatively large and the back is protected by broad, closely-knit armoured plates. The flanks and the outsides of the legs are covered in rounded, pebble-like scales. The snout of this species is very slender and tapering, somewhat resembling the snout of a gharial.

Dwarf/pygmy populations of Freshwater crocodile growing no bigger than 1.5 m (5 ft) have been indentified, but they are not considered subspecies. These small Freshwater crocodiles are darker than their larger counterparts and reach sexual maturity at half the normal size. Their diminutive size may be linked to a scarcity of food. Freshwater crocodiles are known to become smaller and smaller upstream (the largest abundance of food is found downstream).  

Freshwater Crocodile feeding and diet

The slender and tapering snout of the Freshwater crocodile is believed to be an adaptation to a diet consisting chiefly of fish. The Freshwater crocodile is also known to eat other small vertebrates and invertebrates, especially when young. Large adult Freshwater crocodiles can take both aquatic and terrestrial animals and are for instance known to catch fish, amphibians, reptiles, birds and bats. Cannibalism also occurs, especially during periods when food is scarce.

During the dry season, the Freshwater crocodile rarely feeds since there is such as shortage of prey. The low night temperatures during this season also serve to make the crocodile passive.  

Freshwater Crocodile breeding

Males reach sexual maturity at a length of roughly 1.5 m (5 ft), females when they’re slightly smaller. An exception to this rule is the pygmy populations of Freshwater crocodile who attains sexual maturity at half the normal length. Adult freshwater crocodiles have been found returning to breed in the nesting area in which they themselves hatched.

Freshwater crocodiles court each other during the early months of the dry season (around May). When it’s time for egg laying the female crocodile will excavate a hole in a part of the sand embankment that has become exposed by the dry season. Some years the rains arrive early and flood the nests, killing the embryos inside. 

The Freshwater crocodile normally deposits her eggs roughly six weeks after mating and she will place them 12-20 cm (5-8 in) below the surface of the nest. If the eggs are burrowed to shallowly, they risk becoming overheated by the sun. Freshwater crocodiles normally lay eggs at night.  

The nesting period for this crocodile species varies from location to location but generally occurs between July and September. Usually, all the females in a certain location will nest within the same three week period, and it is common for a lot of nests to be excavated near each other. If the nest density becomes too high, females may dig up and destroy the nests of other females.

The average clutch size is13 eggs, but anywhere from 4 to 20 eggs have been reported. Incubation takes 65-95 days during which an average temperature of 30-33° C (86-91° F) is desirable. Embryos incubated at 32° C (89.6° F) become male, while those expose to slightly warmer or cooler conditions become female. Fluctuating nest temperatures are believed to result in greater sexual differentiation.   

The parents will leave the nest unguarded and predation from lizards is common. On average for all nests, no more than one egg out of three survives long enough to hatch. When the young are ready to emerge they will emit chirping sounds that prompts the female to return and help them out of the nest. She may also carry them to the water in her mouth.   

The female will watch over her hatchlings for some time to protect them from predators, but the exact period varies. Compared to the Saltwater crocodile, the Freshwater crocodile leaves her young quite soon.

Freshwater Crocodile facts

Freshwater Crocodile facts # 1
Crocodylus johnstoni is named after Johnston, the first person who reported this species to Krefft. Unfortunately, Krefft misspelled the name "johnsoni" in his initial description and even though he later corrected it, the original error still stands due to the strict rules of the International Commission on Zoological Nomenclature. Most scientific publications do however use the name Crocodylus johnstoni rather than Crocodylus johnsoni.

Freshwater Crocodile facts # 2
Crocodylus johnstoni is known under several different common names in English, such as Freshwater crocodile, Australian freshwater crocodile, Johnston's crocodile, Johnston's river crocodile, Fish crocodile, an the colloquial "Freshie".

Freshwater Crocodile facts # 3
The Freshwater crocodile has sharper, less blunt teeth than the Saltwater crocodile.

Freshwater Crocodile facts # 4
Unlike the Saltwater crocodile which is known to kill and eat humans, there is only one recorded attack by a Freshwater crocodile on a person. This attack, which took place in the Kakadu National Park, resulted in minor injuries only and the attacked person could swim and walk away from the crocodile to safety. The person is believed to have swum directly over the small crocodile.

Freshwater crocodiles normally show aggression toward humans only if they feel threatened. They will normally just ignore people and swimming in waters where Freshwater crocs are present is generally considered safe.  

Freshwater Crocodile facts # 5
Only 1% of all hatchlings survive long enough to reach maturity. Some years, so many eggs and hatchlings are killed that researchers believe no new animals are recruited into the adult population.