Crocodylus johnsoniFreshwater Crocodile, Johnstone River Crocodile

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Geographic Range

This species of crocodile is found in the Northern Territory of Australia and Queensland, and also in northern and western Australia.

Habitat

This species occupies various fresh water areas such as lagoons, rivers, billabongs, and swamps.

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

Physical Description

Crocodylus johnsoni can reach a maximum length of three meters. It has a light brown body with darker bands on its body and tail and lighter brown bands on its snout. It has a morphologically distinct narrow snout with approximately 68-72 teeth total consisting of 5 premaxillary teeth, 14-16 maxillary, and 15 mandibular teeth. The body is covered with scales that are generally large and provide wide armor on the back.

Reproduction

The females nest in holes that are exposed on sandbars during the dry season from August through September. Mating occurs three to six weeks before laying. Clutches average in size between 13-20 eggs and hatch in about 65-95 days. Egg laying usually occurs at night. Eggs are faced with predation by monitor lizards and feral pigs. High and low temperatures (33-34C) produce female embryos while intermediate temperatures (32C) produces male embryos. The nests of eggs are left unguarded, but the mothers reappear in late October. At the end of the incubation period, the mothers carry the newly hatched young to the water in their mouths. The mothers then stay close to the young and protect them for a short period of time. In addition to being hole nesters, they are also sometimes called "pulse nesters" because all females in a given population nest within a brief three week period each season. Individuals reach reproductive maturity when they reach 1.5 meters in length.

  • Key Reproductive Features
  • gonochoric/gonochoristic/dioecious (sexes separate)

Lifespan/Longevity

  • Average lifespan
    Status: captivity
    20 years
    AnAge

Behavior

When hunting, these animals use a sit-and-wait method of grabbing prey with a swift sideways motion of the head.

Food Habits

This creature eats fish, insects, small invertebrates, amphibians, mammals, birds, and other small vertebrates. Large individuals may consume terrestrial prey.

Economic Importance for Humans: Positive

Humans benefit from this species by using it for its meat, eggs, and its leather-producing hide.

Economic Importance for Humans: Negative

Occasional attacks on humans have been reported.

Conservation Status

Long-term aboriginal hunting did not significantly affect the population despite advances made in tanning processes at the end of the 1950s that allowed the skins of this species, instead of those of the preferred saltwater crocodile, to be used as leather. Hunting did cause a decrease in populaton size but protective measures were taken in the early 1960s. In western Australia they were protected by law in 1962, and in 1964 in the Northern Territory. Queensland did not pass its protective laws until 1974. Illegal hunting continues but the main threat is the destruction of habitat. Small scale ranching and farming of these crocodiles exists.

Other Comments

Other common names include: Johnson's/Johnston's (river) crocodile, "Freshie", and fish crocodile. There are no recognized subspecies although darker-colored dwarf specimens have been identified. Also called Crocodylus johnsoni.

Contributors

Nikoma Boice (author), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

References

Grnard, Steve. 1991. Handbook of Alligators and Crocodiles. Florida: Kreger Publishing Company.

Levy, Charles. 1991. Crocodiles and Alligators. London: Quintet Publishing Limited.

Thorbjarnarson, John. 1992. Crocodiles: An Action Plan For Their Conservation. Switzerland, IUCN.

http://www.flmnh.ufl.edu/cnhc/csl.htm