HABITATS HABITATS Within Australia, there are two species of (true) crocodiles: the salt water or estuarine crocodile and the endemic Australian freshwater crocodile. The biology of the two species differ in many ways, crocodiles are restricted to the coastal fringe and the rivers that drain into it. Salt water crocodiles occupy the immediate coastal areas, including tidal and non-tidal rivers. Salt water crocodiles occasionally go long distances upstream into areas dominated by, and considered typical for fresh water crocodiles. Fresh water crocodiles are only sometimes found in tidal, saline areas. With in the northern territory, fresh water crocodiles were protected in 1963, while salt water crocodiles were still being hunted. In 1971 all the saltwater crocodiles were protected, the recovering 'freshies' soon took the place of the 'salties.'
There is a lot of difference in growth rate between the saltwater and the freshwater crocodile. Of lot of this is affected by different factors, sex, season and food has a lot to do with it. Many studies have been conducted in the McKinlay river and now similar studies are beginning in the Katherine River Gorge area. In the McKinlay River, there slight but significant differences in the rate of growth between individuals in the upstream and down stream animals grow faster. There are also very significant differences in the rates at which males and females grow, particularly after 4 years of age: males grow faster. The average freshwater Crocodile egg within the Northern Territory weighs 68 grams and produces a hatchling weighing 42 grams. The dimensions of the average hatchling are: head length 3.74cm; snout to vent length 11.2cm; total length 24.4cm.
The size of the crocodiles hatchling is determined largely by the size of the egg which they come from. Large eggs produce large hatchling, small eggs produce small hatchings. The average saltwater crocodile egg weighs 113 grams and the average hatchling will weigh 72 grams and a total length of 29.3 cm; head length is 4.3 cm and snout to vent length is13.8 cm {the vent is the cloaca or the 'anus'}. Females usually reach maturity at the length of 2.3 metres total length and it takes them a minimum of 12 years to reach that size. Males mature at around 3.35 metres and it will take around 16 years. In some crocodile farms it will only be 3 metres to mature, and females around 2.1 metres and that may take only 6 to 7 years.
Shane Langhans, Herberton, Queensland, Australia
References
Biddell Crocodiles of Australia Adventure Publishing Australia
Picture from The Down Under Collection Delux, New Horizons, Armidale, Australia, 1995.