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Australian Freshwater Crocodile (Johnston's, Johnson's, Johnstone's Crocodile)


Image (c) Adam Britton, crocodilian.com

Has an unusually long snout


Order: Crocodylia

Family: Crocodylidae

Subfamily: Crocodylinae

Genus & Species: Crocodylus johnstoni (Crocodylus johnsoni)

APPEARANCE

The Australian freshwater crocodile is a small cousin of the Australian saltwater crocodile. Sexual dimorphism is present in this species, with males being larger than females. The males reach lengths of 8-10 ft max (2.4-3 m) and weigh 40 lbs (90 kg). The females reach lengths of 7.8 ft (2.3 m) and weigh 20 lbs (45 kg). Although there are no subspecies, smaller, darker- coloured populations can be found farther upstream, perhaps due to food availability. They reach lengths of 5 ft (1.5 m). Australian freshwater crocodiles grow very slowly, and may not reach full lengths for 20 years.

Australian freshwater crocodiles have unusually narrow, tapering snouts, being rivaled by that of the gavial. The mouth is lined with 68-72 sharp teeth. The fourth tooth on either side of the bottom jaw is larger than the others, and can be seen when the mouth is closed, fitting into a notch on the upper jaw. The eyes have a special clear eyelid called a nictitating membrane, which protects the eyes while underwater.

Australian freshwater crocodiles have strong legs with clawed, webbed feet. The tail is very powerful. The skin is light brown in colour, with dark bands on the body and tail and sometimes on the snout. The scales are large, with wide plates on the back and ventral osteoderms (bony plates) on the belly. The flanks and outside of the legs are covered in pebbly scales.

Australian freshwater crocodiles are one of the few species that can gallop on land, reaching speeds of 18 km/h. They have a life span of 50 years.

HABITAT

Australian freshwater crocodiles are found only in the provinces of Queensland, Northern Territory, and Western Australia in Australia. They are found predominately in freshwater lakes, billabongs, swamps, rivers, creeks, and wetlands, although not by choice. The Australian saltwater crocodile keeps them out of more saline (salty) areas by outcompeting them. However, when this species was near extinction Australian freshwater crocodiles could be found in saltwater. Today, they are found mainly in freshwater and brackish areas. They are not fussy over water, and will live in muddy, clear, fast, still, deep, or shallow water. After the rainy season they move to more permanent areas of water that will not dry up in the dry season, and will rarely eat and hardly grow until they return at the start of the next rainy season.

FOOD

Australian freshwater crocodile juveniles feed on insects, crustaceans, and small fish. Larger and older crocodiles feed on the same things, as well as larger prey such as amphibians, reptiles, bats, large fish, and land mammals that come close to the water. They can also be cannibalistic and will eat juveniles. They do not hunt on land but will wait at the water's edge for prey, typically fish, to get close, and then will attack with a lightning-fast snap of the head. They also hunt underwater. They swallow stones to aide in digestion, and drink only freshwater, not saltwater.

ENEMIES

Although they have osteoderms, Australian freshwater crocodiles where still hunted for their hide for 14 years when Australian saltwater crocodiles were no longer abundant. Australian freshwater crocodiles were then considered rare, and hunting was stopped in the 1960's and 1970's. It wasn't until the 1980's that their populations became stable. Today they are hunted by aboriginals for food.

Juveniles are killed by the adults when food is scarce. They are also eaten by black kites, whistling kites, turtles, and large fish. Gould's monitor lizards, sand goannas, and feral pigs also keep the numbers down by destroying 80% of Australian freshwater crocodile nests. Habitat loss to farmland is also a major threat. They are considered to be low risk.

BREEDING

Sexual maturity for females is reached at 11-14 years, for the males 16-17 years. The breeding season is from September to October. Hole nests are dug in the river bank by the females, and are generally dug 50 ft (15 m) away from the water's edge and are 5 in (12 cm) deep. Anywhere from 4-21 eggs are laid, and they hatch after an incubation period of 6-10 weeks. The temperature of the nest determines the sex of the juveniles: 31-31 C males, above and below that mostly females. When the eggs are ready to hatch, a female (not necessarily the parent) digs out the nest and crushes the eggs to release the juveniles, even though they have an egg tooth and could get out themselves. The juveniles sometimes get injured by her sharp teeth as she carries them to the water's edge. Less than 1% of the eggs laid will become mature Australian freshwater crocodiles.

RELATIVES

There are no subspecies. There are 23 species of crocodilians found worldwide.

RESOURCES CITED

1. www.flmnh.ufl.edu/natsci/herpetology/brittoncrocs/csp_cjohn.htm
2. www.flmnh.ufl.edu/natsci/herpetology/act-plan/cjohn.htm
3. www.kingsnake.com/oz/crocs/johnstoni.htm
4. mag-nify.educ.monash.edu.au/acps99/Freshwcrocodile.htm
5. www.milamba.com/australia/inhabit/reptiles/rep10.htm
6. link.springer.de/link/service/journals/00360/bibs/9169003/91690215.htm
7. www.bitme.com.au/aviary/crocodiles.html

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