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Johnston’s Crocodile

Order: Crocodylia
Family: Crocodylidae
Genus/species: Crocodylus johnstoni

Johnston’s crocodile is a relatively small crocodile and some males reach a maximum length of only ten feet (3 m). It has a light brown body with darker bands on its body and tail and lighter brown bands on its snout. It has a distinctly narrow snout with about 68 to 72 teeth total. The body is covered with scales that are generally large and provide wide armor on their back.

Distribution and Habitat
This species of crocodile inhabits the Northern Territory of Australia and Queensland and also northern and western Australia.

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

Diet in the Wild
The shape of the snout, like that of the gharial, suggests a primary adaptation to a piscivorous (fish-based) diet. This creature also eats insects, small invertebrates, amphibians, mammals, and birds. Large individuals may consume terrestrial prey. This crocodile favors a sit-and-wait hunting strategy, snatching prey up with a lightning-fast sideways movement of the head. It rarely feeds during the dry season because of a lack of available prey and a reduction in available habitat due to drying of pools and rivers.

Zoo Diet
They are fed mice, rats, and fish.

The males reach sexual maturity around five feet (1.5 m) and the females when only slightly smaller. The females nest in holes that are exposed on sandbanks during the dry season from August through September. Mating occurs three to six weeks before laying.

Clutches average in size between 13 and 20 eggs and hatch in about 65 to 95 days. Egg laying usually occurs at night. Eggs are lost to predation by monitor lizards and feral pigs. Temperatures between 86 and 91° F (30 to 33° C) are desirable. Temperature of 89° F (32° C) produces male embryos, whereas those a couple of degrees cooler or warmer produce females.

The nests are left unguarded, but the mothers reappear in late October at the end of the incubation period. The mothers then carry the newly hatched young to the water in their mouths. The mothers 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.

Only one percent of these hatchlings will survive to reach maturity, and in some years predation pressures are so high that it is unlikely that any new animals are recruited into the adult population. In some years, early rains at the end of the dry season may destroy almost all the nests through flooding. Juveniles that survive to maturity have been found returning to the same breeding and nesting areas.

Life Span

Long-term aboriginal hunting did not significantly affect the population. Advances made in tanning processes at the end of the 1950s allowed the skins of this species, instead of those of the saltwater crocodile, to be used as leather. As a result, hunting increased. This hunting did cause a decrease in population 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.

Population estimates vary, as the species can be difficult to survey effectively, but it is not unreasonable to assume that there are at least 100,000 individuals in the wild.

Fun Facts
In Australia these crocodiles are also called the Australian freshwater crocodile or “Freshie.”

Source of Information
All or part of this information was provided by the Animal Diversity Web and Museum of Zoology of the University of Michigan.
It appears here with their permission. The original author of this information was Nikoma Boice.

For more information, including references, see the Animal Diversity Web account for this species, here:
http://animaldiversity.ummz.umich.edu/ site/ accounts/ information/ Crocodylus_johnstoni.html.