Crocodiles

Australian freshwater crocodiles (Crocodylus johnstoni KREFFT 1873) are endemic to Australia and are distributed throughout the coastal and more inland regions of the north, from Western Australia to Queensland.

Freshwater crocodiles are generally found upstream of tidal influence, in lower salinity water. They are actually fairly tolerant of saltwater, yet saltwater crocodiles (Crocodylus porosus) aggressively outcompete them in most areas where they occur. Main habitats include wetlands, rivers, creeks, freshwater billabongs and swamps. They display fairly wide habitat preferences (clear water, muddy, still, fast flowing, shallow or deep).

At the end of the wet season (in April), freshwater crocodiles move to areas of more permanent water for the duration of the dry season. Feeding and growth normally cease entirely. Some individuals may burrow into river banks, and well-established burrows exist. At the end of the dry season, they relocate to wet season habitat using a well-honed homing instinct. They use the wet season for feeding and dispersal.

Larger adults eat similar, but larger prey. Unlike saltwater crocodiles, adult freshwater crocodiles will still take small prey as well as larger prey such as amphibians, reptiles, bats, birds, and primarily fish (for which their jaws are suited).

Feeding tactics involve waiting at the water's edge for prey to come within range. They do not hunt on land, but will take terrestrial prey close to the water's edge. Larger animals will sneak up on prey in the water, submerging some distance away, and attacking from below.

They ingest small stones and pebbles called "gastroliths" which are used in digestion (to grind up food in the gizzard), and also to aid in maintaining buoyancy in larger animals (by acting as a ballast).

Courtship occurs in the middle of the dry season during July, and nesting occurs over a 2 to 3 week period during August. Freshwater crocodiles dig hole nests in sandy river banks, as nesting materials are unavailable during the dry season. As the eggs are closer to the ground water table, they are more susceptible to flooding at the start of the wet season - particularly if heavy rains occur early. The nest is normally dug within 15 metres of the water, and egg laying occurs at night to reduce risk to the female.

Female freshwater crocodiles are known to dig communal nests, within one or two metres of each other. Females sometimes accidentally dig up the eggs of other females while digging their own hole. Females tend to return to the same nesting sites year after year.

Although the female remains close to the nest, she generally does a poor job of defending it. Hunting from Aboriginals may have changed this behaviour over time by making females more wary of intruders. Most nests (over 80%) are destroyed by predators such as Varanus gouldi (Gould's monitor), Varanus panoptes (sand goanna) and feral pigs (Sus scrofa).

Mean clutch size is around 13 eggs, although studies in Queensland indicate slightly larger clutches may occur there. The largest clutches are laid at the start of the nesting period. Incubation period is around 74 to 80 days, depending upon temperature.

Females revisit the nest site around hatching. Vibration (caused by the female traversing the area) stimulates the hatchlings to call from within the eggs, which in turn stimulates the female to begin opening the nest. The nest-opening female may not necessarily be the parent.

Hatchlings possess a small egg tooth to split the egg membrane, but they are often assisted by the female who will gently crush the egg shell to open it. She will then carry hatchlings to the water in her mouth (which distends to carry several), although sometimes injuries to the hatchlings can occur from her sharp teeth.

Hatchlings form a creche (less than 10 animals usually), with which the female may remain for a few weeks. Hatchlings produce agitated vocalisations if disturbed which warns other hatchlings, and attracts the female. Freshwater crocodiles tend to be less vigilant than saltwater crocodiles, however, and the hatchlings disperse more quickly.

Hatchling predators include birds (e.g. black and whistling kites), other crocs, turtles and even large fish. Like saltwater crocodiles, it is cannibalism which is one of the major causes of mortality in young crocodiles.

Growth is highly variable, and is influenced by environmental, habitat, genetic and dietary factors. Nearly all growth occurs during the wet season, where food intake is high. Freshwater crocodiles grow much more slowly than saltwater crocodiles.

Size: males reach 2.4 - 3.0 m (53 kg) or 8 - 10 feet maximum, females reach 2 m (6.5 feet) maximum. Age: maximum rarely exceeds 50 years. It takes 20 years for a juvenile to grow to its maximum size, although growth will continue at a slower rate throughout life (hence it is difficult to predict maximum size). Growth is also affected by food intake, temperatures, and social factors (e.g. stress).

Freshwater crocodiles were hunted for 4 years in N.T. and 14 years in Queensland. In that time, the population went from being "plentiful" to being "rare". They were protected in 1962 (N.T.), 1964 (W.A.) and 1974 (Qns.). It took until 1980 for the population to show significant recovery.

The population of crocodiles (saltwater and freshwater) is kept in check by cannibalism - larger crocodiles are a significant cause of juvenile mortality. The more adult crocodiles around, the greater the degree of population control on the juveniles. This aspect to the population balance is one of the many things disrupted by excessive poaching / hunting of adults. Today, there is no harvesting of freshwater crocodiles as their skin is worth very little next to a saltwater crocodile's skin.

The major current threat to the population is habitat loss for farmland and development, although freshwater crocodiles are not considered to be under immediate threat. Remaining habitat therefore needs to be given some "income earning" potential - i.e. some value.

Largest living crocodilian species with a confirmed measurement, and in fact the world's largest living reptile in terms of mass. Adult males can reach sizes of up to 6 or 7 metres (20 to 23 feet), the largest confirmed individual being 20.7 feet (6.3 metres). There is always a lot of interest over the largest ever recorded saltie. In general, males over 5 m (17 feet) in length are extremely rare. Females are smaller, the normal maximum adult size being 2.5 m to 3 m (8 to 10 feet) being the normal maximum adult size. Maximum weight varies, but has been known to exceed 1,000 kg in 18 to 19 foot adults. 5 metre adults are closer to 400 to 500 kg.

This is a large-headed species with a heavy set of jaws. A pair of ridges run from the eye orbits along the centre of the snout, becoming more distinct with age. The upper surface of the top jaw becomes very rugose in large adult males. Scales on the flanks are more oval in shape than other species, although belly scales are rectangular, even and relatively small. Osteoderms are restricted to the back and a small nuchal cluster on the neck.

Juveniles are normally pale tan in colour with black stripes and spots on the body and tail. A small percentage of animals in some regions tend to be much lighter in colour (hypomelanistic), although very dark (hypermelanistic) animals are occasionally also seen. The juvenile colouration persists for several years, growing progressively paler and less colourful with more indistinct bands which never completely disappear, although are rarely visible in adults except in clear water. Mature adults are generally dark, with lighter tan or grey areas. The ventral surface (belly) is creamy yellow to white in colour, except the tail which tends to be more grey on the underside nearer the tip. Dark bands and stripes are present on the lower flanks, but do not extend onto the belly region.

Saltwater crocodiles take a wide variety of prey, although juveniles are restricted to smaller items such as insects, amphibians, crustaceans, small reptiles and fish. The larger the animal grows, the greater the variety of items that it includes in the diet, although relatively small prey still make up the majority of the diet even in large adults. Prey items include crustaceans (e.g. mudcrabs) and vertebrates (e.g. turtles, goannas, snakes, shore and wading birds). Large adults occasionally take much larger prey include buffalo and domestic livestock, wild boar, monkeys etc.

Breeding territories are established in freshwater areas. Females reach sexual maturity at lengths of 2.2 to 2.5 m (10 to 12 years old). Males mature later (3.2 m, at around 16 years old). 40 to 60 eggs are usually laid (can range from 25 to 90) in mound nests made from plant matter and mud. These are constructed between the months of November and March during the wet season - this serves to raise the eggs above the ground to help prevent losses due to flooding. Many nests are still flooded every year, however, killing all the unhatched embryos. Alternately, if the nest is in danger of getting too dry, the female has apparently been observed to splash water onto it from a purpose-dug, adjacent pool.

Although the female stays near the nest, some eggs do fall foul of predators (e.g. monitor lizards, feral wild pigs in Australia) and human egg collectors. Juveniles hatch after around 90 days, although this varies with nest temperature. The female digs the neonates out of the nest when they start their characteristic chirping sounds, assisting them to the water by carrying them in her mouth.

Much research has been carried out into TSD (Temperature-dependant Sex Determination) in this species, which is of value for captive breeding programs to ensure the correct sex ratio, or to produce faster growing males for farming purposes. The highest percentage of males are produced around 31.6°C, with more females a few degrees above and below this. It is estimated that less than 1% of hatchlings will survive to reach maturity, given predation (e.g. turtles, goannas, C. johnstoni) and social pressures (territorial males will kill and eat juveniles - they are one of the main limiting factors in population growth along with competition).

Many species of crocodilians are falsely viewed as man-eaters, but fear of this species is not unfounded, with a number of people injured or killed each year, although in most cases these tragedies can be avoided with increased awareness. However, loss of life has led to a degree of antipathy towards the species, making conservation measures more difficult to implement.

Given its relatively wide distribution, control of trade can be very difficult. The commercial value of the hide is very high (the most valuable of any crocodile species), due to the lack of ventral osteoderms which otherwise make tanning difficult, and the size and shape of the belly scales. Unregulated hunting mainly between 1945 and 1970 caused a dramatic decline throughout the range of the species. This has been controlled in some areas, notably Australia, but threats from habitat destruction still exist. Protection in some countries is often ineffective, and while illegal trade is relatively insignificant now for this species, killing due to fear is becoming an increasing problem.

Australia has been the centre for most of the extensive research carried out on this species, and several model breeding and conservation programs exist there. It is estimated that there are at least 100,000 to 150,000 crocodiles in the northern three states of Australia (Western Australia, Queensland and Northern Territory where the largest population base exists), so the problem has now shifted to one of persuading landowners and public alike of the value of the species which is otherwise only seen as destructive.

Sustainable use programs have been implemented in the Northern Territory, and have proven to be highly successful in giving people an incentive to preserve not only the crocodiles but more importantly the habitat which supports them. These primarily involve collection of eggs from wild nests, with payment for the eggs being given to the landowners. The hatchlings are then sold to crocodile farms for raising and skin production.

Extensive surveys are conducted with the harvesting, which has demonstrated no detectable impact of the harvesting program on population growth. A trial harvest of wild, adult crocodiles involving aboriginal communities was started in 1997 - the first time crocodiles had been legally hunted in the Northern Territory for 26 years.

Although populations are recovering in some areas, others are less positive. Habitat destruction and illegal hunting can be major problems (e.g. Irian Jaya). The population in Sri Lanka is in grave danger of extirpation due to local fears and attitudes, linked with habitat removal. Feral buffalo populations in Australia have destroyed nesting habitat in the Northern Territory, although feral eradication programs have reduced this problem considerably. Restocking programs in India (Bhitarkanika National Park in Orissa) have met with success, showing potential for other areas, although these need to be found. A sustainable use program established in Papua New Guinea has set the standard for similar projects in this and other species of crocodilian. These are based upon both wild cropping and ranching schemes. Farming in other areas (particularly Australia) is now performed on a large scale. Despite this, basic survey information is still lacking in other parts of this species' range (e.g. Indonesia).

The future of the species seems to be very secure at the moment, given the large population bases in Australia and Papau New Guinea. However, it is likely that the range of the species will be severely reduced through extirpation of many small populations in various countries unless management programs can be implemented, or more effective control and protection set up. The idea of sustainable use remains controversial, yet it is has been clearly demonstrated to be effective in the conservation of this species. The only areas where the species is likely to disappear are those where proper management and conservation programs do not sufficiently protect the wild populations.


	Alexahnder's Amazing Animals home Where The Original Traps Were Set \| Equipment In The Original Traps \| Bait For The Original Traps \| What I Found In The Original Traps \| WHAT IS CREST??? \| Crickets \| Fruit Flies \| Giant Burrowing Cockroaches \| The Crocodile Hunter \| Venomous Snakes \| Crocodiles \| Vote 1 \| Related Links \| Comments \| Chat Room \| Contact Me Crocodiles FRESHWATER CROCODILES Distrubrution of freshwater crocodiles (C Johnstoni) Australian freshwater crocodiles (Crocodylus johnstoni KREFFT 1873) are endemic to Australia and are distributed throughout the coastal and more inland regions of the north, from Western Australia to Queensland. Freshwater crocodiles are generally found upstream of tidal influence, in lower salinity water. They are actually fairly tolerant of saltwater, yet saltwater crocodiles (Crocodylus porosus) aggressively outcompete them in most areas where they occur. Main habitats include wetlands, rivers, creeks, freshwater billabongs and swamps. They display fairly wide habitat preferences (clear water, muddy, still, fast flowing, shallow or deep). At the end of the wet season (in April), freshwater crocodiles move to areas of more permanent water for the duration of the dry season. Feeding and growth normally cease entirely. Some individuals may burrow into river banks, and well-established burrows exist. At the end of the dry season, they relocate to wet season habitat using a well-honed homing instinct. They use the wet season for feeding and dispersal. Feeding Hatchlings first absorb their yolk sac, on which they can thrive for days and even weeks if necessary. Juveniles eat small prey - e.g. insects and other arthropods, crustaceans, small fish Larger adults eat similar, but larger prey. Unlike saltwater crocodiles, adult freshwater crocodiles will still take small prey as well as larger prey such as amphibians, reptiles, bats, birds, and primarily fish (for which their jaws are suited). Feeding tactics involve waiting at the water's edge for prey to come within range. They do not hunt on land, but will take terrestrial prey close to the water's edge. Larger animals will sneak up on prey in the water, submerging some distance away, and attacking from below. They ingest small stones and pebbles called "gastroliths" which are used in digestion (to grind up food in the gizzard), and also to aid in maintaining buoyancy in larger animals (by acting as a ballast). Nesting Courtship occurs in the middle of the dry season during July, and nesting occurs over a 2 to 3 week period during August. Freshwater crocodiles dig hole nests in sandy river banks, as nesting materials are unavailable during the dry season. As the eggs are closer to the ground water table, they are more susceptible to flooding at the start of the wet season - particularly if heavy rains occur early. The nest is normally dug within 15 metres of the water, and egg laying occurs at night to reduce risk to the female. Female freshwater crocodiles are known to dig communal nests, within one or two metres of each other. Females sometimes accidentally dig up the eggs of other females while digging their own hole. Females tend to return to the same nesting sites year after year. Although the female remains close to the nest, she generally does a poor job of defending it. Hunting from Aboriginals may have changed this behaviour over time by making females more wary of intruders. Most nests (over 80%) are destroyed by predators such as Varanus gouldi (Gould's monitor), Varanus panoptes (sand goanna) and feral pigs (Sus scrofa). Mean clutch size is around 13 eggs, although studies in Queensland indicate slightly larger clutches may occur there. The largest clutches are laid at the start of the nesting period. Incubation period is around 74 to 80 days, depending upon temperature. As with all crocodilians, sex is determined by temperature during incubation. Between 31 and 32 degrees C, mostly males are produced. More females are produced at warmer and cooler temperatures. Females revisit the nest site around hatching. Vibration (caused by the female traversing the area) stimulates the hatchlings to call from within the eggs, which in turn stimulates the female to begin opening the nest. The nest-opening female may not necessarily be the parent. Eggs start off translucent, and quickly become opaque due to fluid absorption from the albumen. Hatchlings possess a small egg tooth to split the egg membrane, but they are often assisted by the female who will gently crush the egg shell to open it. She will then carry hatchlings to the water in her mouth (which distends to carry several), although sometimes injuries to the hatchlings can occur from her sharp teeth. Hatchlings form a creche (less than 10 animals usually), with which the female may remain for a few weeks. Hatchlings produce agitated vocalisations if disturbed which warns other hatchlings, and attracts the female. Freshwater crocodiles tend to be less vigilant than saltwater crocodiles, however, and the hatchlings disperse more quickly. Hatchling mean mass is around 42 grams, and the mean size is around 24 cm. Hatchling predators include birds (e.g. black and whistling kites), other crocs, turtles and even large fish. Like saltwater crocodiles, it is cannibalism which is one of the major causes of mortality in young crocodiles. Initial predation is very high, and less than 1% of all the initial eggs laid will produce a mature adult crocodile. Growth Growth is highly variable, and is influenced by environmental, habitat, genetic and dietary factors. Nearly all growth occurs during the wet season, where food intake is high. Freshwater crocodiles grow much more slowly than saltwater crocodiles. Size: males reach 2.4 - 3.0 m (53 kg) or 8 - 10 feet maximum, females reach 2 m (6.5 feet) maximum. Age: maximum rarely exceeds 50 years. It takes 20 years for a juvenile to grow to its maximum size, although growth will continue at a slower rate throughout life (hence it is difficult to predict maximum size). Growth is also affected by food intake, temperatures, and social factors (e.g. stress). Males reach sexual maturity at 87 cm SVL (snout vent length) at 16 - 17 years old. Females mature earlier at 74 - 78 cm SVL, around 11 - 14 years old. Conservation Freshwater crocodiles were hunted for 4 years in N.T. and 14 years in Queensland. In that time, the population went from being "plentiful" to being "rare". They were protected in 1962 (N.T.), 1964 (W.A.) and 1974 (Qns.). It took until 1980 for the population to show significant recovery. The population of crocodiles (saltwater and freshwater) is kept in check by cannibalism - larger crocodiles are a significant cause of juvenile mortality. The more adult crocodiles around, the greater the degree of population control on the juveniles. This aspect to the population balance is one of the many things disrupted by excessive poaching / hunting of adults. Today, there is no harvesting of freshwater crocodiles as their skin is worth very little next to a saltwater crocodile's skin. The major current threat to the population is habitat loss for farmland and development, although freshwater crocodiles are not considered to be under immediate threat. Remaining habitat therefore needs to be given some "income earning" potential - i.e. some value. Public education is also important. Freshwater crocodiles are not considered "dangerous", unlike saltwater crocodiles, but their bite can still inflict serious injury if they are provoked. Written by Adam Britton, PhD. http://www.kingsnake.com/oz/crocs/johnstoni.htm SALTWATER CROCODILES APPEARANCE: Largest living crocodilian species with a confirmed measurement, and in fact the world's largest living reptile in terms of mass. Adult males can reach sizes of up to 6 or 7 metres (20 to 23 feet), the largest confirmed individual being 20.7 feet (6.3 metres). There is always a lot of interest over the largest ever recorded saltie. In general, males over 5 m (17 feet) in length are extremely rare. Females are smaller, the normal maximum adult size being 2.5 m to 3 m (8 to 10 feet) being the normal maximum adult size. Maximum weight varies, but has been known to exceed 1,000 kg in 18 to 19 foot adults. 5 metre adults are closer to 400 to 500 kg. This is a large-headed species with a heavy set of jaws. A pair of ridges run from the eye orbits along the centre of the snout, becoming more distinct with age. The upper surface of the top jaw becomes very rugose in large adult males. Scales on the flanks are more oval in shape than other species, although belly scales are rectangular, even and relatively small. Osteoderms are restricted to the back and a small nuchal cluster on the neck. Juveniles are normally pale tan in colour with black stripes and spots on the body and tail. A small percentage of animals in some regions tend to be much lighter in colour (hypomelanistic), although very dark (hypermelanistic) animals are occasionally also seen. The juvenile colouration persists for several years, growing progressively paler and less colourful with more indistinct bands which never completely disappear, although are rarely visible in adults except in clear water. Mature adults are generally dark, with lighter tan or grey areas. The ventral surface (belly) is creamy yellow to white in colour, except the tail which tends to be more grey on the underside nearer the tip. Dark bands and stripes are present on the lower flanks, but do not extend onto the belly region. DIET: Saltwater crocodiles take a wide variety of prey, although juveniles are restricted to smaller items such as insects, amphibians, crustaceans, small reptiles and fish. The larger the animal grows, the greater the variety of items that it includes in the diet, although relatively small prey still make up the majority of the diet even in large adults. Prey items include crustaceans (e.g. mudcrabs) and vertebrates (e.g. turtles, goannas, snakes, shore and wading birds). Large adults occasionally take much larger prey include buffalo and domestic livestock, wild boar, monkeys etc. BREEDING: Breeding territories are established in freshwater areas. Females reach sexual maturity at lengths of 2.2 to 2.5 m (10 to 12 years old). Males mature later (3.2 m, at around 16 years old). 40 to 60 eggs are usually laid (can range from 25 to 90) in mound nests made from plant matter and mud. These are constructed between the months of November and March during the wet season - this serves to raise the eggs above the ground to help prevent losses due to flooding. Many nests are still flooded every year, however, killing all the unhatched embryos. Alternately, if the nest is in danger of getting too dry, the female has apparently been observed to splash water onto it from a purpose-dug, adjacent pool. Although the female stays near the nest, some eggs do fall foul of predators (e.g. monitor lizards, feral wild pigs in Australia) and human egg collectors. Juveniles hatch after around 90 days, although this varies with nest temperature. The female digs the neonates out of the nest when they start their characteristic chirping sounds, assisting them to the water by carrying them in her mouth. Much research has been carried out into TSD (Temperature-dependant Sex Determination) in this species, which is of value for captive breeding programs to ensure the correct sex ratio, or to produce faster growing males for farming purposes. The highest percentage of males are produced around 31.6°C, with more females a few degrees above and below this. It is estimated that less than 1% of hatchlings will survive to reach maturity, given predation (e.g. turtles, goannas, C. johnstoni) and social pressures (territorial males will kill and eat juveniles - they are one of the main limiting factors in population growth along with competition). CONSERVATION: Many species of crocodilians are falsely viewed as man-eaters, but fear of this species is not unfounded, with a number of people injured or killed each year, although in most cases these tragedies can be avoided with increased awareness. However, loss of life has led to a degree of antipathy towards the species, making conservation measures more difficult to implement. Given its relatively wide distribution, control of trade can be very difficult. The commercial value of the hide is very high (the most valuable of any crocodile species), due to the lack of ventral osteoderms which otherwise make tanning difficult, and the size and shape of the belly scales. Unregulated hunting mainly between 1945 and 1970 caused a dramatic decline throughout the range of the species. This has been controlled in some areas, notably Australia, but threats from habitat destruction still exist. Protection in some countries is often ineffective, and while illegal trade is relatively insignificant now for this species, killing due to fear is becoming an increasing problem. Australia has been the centre for most of the extensive research carried out on this species, and several model breeding and conservation programs exist there. It is estimated that there are at least 100,000 to 150,000 crocodiles in the northern three states of Australia (Western Australia, Queensland and Northern Territory where the largest population base exists), so the problem has now shifted to one of persuading landowners and public alike of the value of the species which is otherwise only seen as destructive. Sustainable use programs have been implemented in the Northern Territory, and have proven to be highly successful in giving people an incentive to preserve not only the crocodiles but more importantly the habitat which supports them. These primarily involve collection of eggs from wild nests, with payment for the eggs being given to the landowners. The hatchlings are then sold to crocodile farms for raising and skin production. Extensive surveys are conducted with the harvesting, which has demonstrated no detectable impact of the harvesting program on population growth. A trial harvest of wild, adult crocodiles involving aboriginal communities was started in 1997 - the first time crocodiles had been legally hunted in the Northern Territory for 26 years. Some discussion of safari-style hunting is now taking place, directed by traditional Aboriginal landowners, but such programs are yet to be implemented. Although populations are recovering in some areas, others are less positive. Habitat destruction and illegal hunting can be major problems (e.g. Irian Jaya). The population in Sri Lanka is in grave danger of extirpation due to local fears and attitudes, linked with habitat removal. Feral buffalo populations in Australia have destroyed nesting habitat in the Northern Territory, although feral eradication programs have reduced this problem considerably. Restocking programs in India (Bhitarkanika National Park in Orissa) have met with success, showing potential for other areas, although these need to be found. A sustainable use program established in Papua New Guinea has set the standard for similar projects in this and other species of crocodilian. These are based upon both wild cropping and ranching schemes. Farming in other areas (particularly Australia) is now performed on a large scale. Despite this, basic survey information is still lacking in other parts of this species' range (e.g. Indonesia). The future of the species seems to be very secure at the moment, given the large population bases in Australia and Papau New Guinea. However, it is likely that the range of the species will be severely reduced through extirpation of many small populations in various countries unless management programs can be implemented, or more effective control and protection set up. The idea of sustainable use remains controversial, yet it is has been clearly demonstrated to be effective in the conservation of this species. The only areas where the species is likely to disappear are those where proper management and conservation programs do not sufficiently protect the wild populations. http://www.flmnh.ufl.edu/natsci/herpetology/brittoncrocs/csp_cpor.htm