Johnston’s Crocodile
Taxonomy
Order: Crocodylia
Family: Crocodylidae
Genus/species: Crocodylus johnstoni
Description
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.
Reproduction
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
Unknown.
Status
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.
