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Facts on Biodiversity & Human Well-being
 

 

Estuarine Crocodile - Crocodylus porosus


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Estuarine Crocodile - Crocodylus porosus Schneider, 1801

IUCN STATUS CATEGORY Removed from Red List

HABITAT Typically occurs in brackish waters, inhabiting large river estuaries and deltas with associated coastal mangrove swamp-forest, but also extends into deep rivers far above tidal influence. Also occurs in freshwater pools and swamps. The Estuarine Crocodile is now restricted through much of its range to the mangrove system as in India, Southeast Asia and Indonesia. In Australia many crocodiles occur in tidal reaches with mangrove vegetation, and also occur in adjacent floodplain billabongs and spring-fed swamps. They may also extend 150km upstream into freshwater non-tidal areas.

GEOGRAPHICAL SPREAD This is a widespread species occurring from Sri Lanka, eastern India and Bangladesh through coastal Southeast Asia to the Philippines, Federated States of Micronesia, and south through Indonesia to Papua New Guinea and northern Australia, east to the Solomon Islands and Vanuatu. Wandering individuals have been and recorded from localities far outside the known breeding range such as the Fiji Islands and Cocos-Keeling Islands.

CURRENT POPULATION Populations have been severely depleted and are at risk throughout its range. Adequate population levels are maintained in only a few localities, notably parts of northern Australia and parts of New Guinea. In Australia the upper-limit estimate for non-hatchling Estuarine Crocodiles is about 15,500. In Bangladesh current population is estimated at less than 200 individuals in an area c. 780 sq. km. In India the total population may be 170 to 330. In Kalimantan a survey in 1972 of 200 miles of the Mahakan River revealed only two adult crocodiles. Widespread in Papua New Guinea but depleted through its accessible range. Perhaps up to 300 individuals in the Solomon Islands. An estimated 375 individuals in Sri Lanka. Very rare in Vanuatu.

SIZE May exceed 7 metres but usually much less. M male length 4.2 to 4.8m.

WEIGHT Male about 408 to 520kg (Guiness Book of Records).

AVERAGE LIFE EXPECTANCY Unknown, but may live to over 65 years.

NORMAL DIET A carnivorous species and a largely opportunistic feeder. In juveniles small fish are taken but crustaceans and insects comprise the main part of the diet. Larger juveniles take more vertebrate prey. Food items include sharks, archer fish, barramundi and mangrove snakes. Riverine birds and mammals may also be taken. As size increases an individual become able to deal with progressively larger prey such as turtles, cattle, horses and humans. Virtually any mammal at the water's edge will be attacked. Large crocodiles may be cannibalistic and will take other hatchlings and small juveniles

NORMAL LIFESTYLE Feeding occurs during the day and night, when food is available. They are mainly shallow water or edge feeders. Sexual maturity appears to be obtained at around 3.2m, 16 years in males and 2.2m, 10 years in females. The grouping behaviour shown by hatchlings is lost at about 8 months and territorial behaviour begins at about 2.5 years, several years before first breeding. Nesting varies with localities although it usually coincides with the wet season. Nesting may be spread over a three to five month period and females at a given locality nest asynchronously. In Papua New Guinea nesting occurs September to January and begins with or before the rains. Mound shaped nests are constructed of a variety of vegetable debris and sometimes a volume of mud. In coastal swamps almost all nests are constructed on floating mats of vegetation. The clutch comprises 25 to 90 eggs. The incubation period is 80 to 90 days although this can be greatly extended at low temperatures. The females stays near the nest for much of the incubation period and so is vulnerable to hunters. Females gather hatchlings in the throat pouch in times of danger and carry them from the nest to the water.

PREVIOUS GEOGRAPHICAL SPREAD Formerly extended to the Cochin area on the west coast of India and possibly to southern China. Once occurred in Singapore but now extinct in the wild, however there is now a captive breeding programme at Jurong.

REASONS FOR DECLINE Commercial hunting for hide along with loss of habitat has drastically depleted populations. During the 1950s and 1960s hunting with high powered rifles and motor boats was carried out on a large scale due to a rapid increase in the price of reptile leather. It was estimated that hundreds of thousands of crocodile were killed annually. In the Republic of Palau, Caroline Islands there was an official programme of extermination which occurred from 1966 to 1981 resulting in this species becoming extremely endangered.

CURRENT THREATS Hunting pressure is still high as the skins are very valuable. The preferred skins are from crocodiles between 0.75 and 1.50m in length, so larger crocodile are not the most commercially viable. The collection of eggs and young for farm rearing to marketable size poses a further threat. Several rearing farms operate in Indonesia (Java and Kalimantan) dependent on eggs and young taken from wild populations. Habitat loss reduces the prospects of recovery of populations already depleted by hunting. In Australia the nesting habitat of Northern Territory is being destroyed by trampling by feral water buffaloes. The anchorage of floating mats of vegetation is being broken down so that the mat drifts away during the wet season on rivers such as the South Alligator. The second most important factor is the toleration of net fishing for barramundi well upstream of tidal river mouths and often right up into breeding areas. Another factor is animosity toward crocodiles, often directed at the Estuarine Crocodile, a large animal which eats humans and is aggressive when encountered near a nest. This species is used for food - eggs are heavily collected in the Andamans - and for medicine. Eggs and meat are consumed in Papua New Guinea.

CONSERVATION PROJECTS Nominally protected by legislation in Australia, Bangladesh, India, Indonesia, parts of Malaysia (Sabah), Sri Lanka. Export of animals and products is prohibited in Australia, India and Sri Lanka. The species occurs in reserve areas in Australia such as the Ord River Nature Reserve in Western Australia and a sizeable freshwater population exists in Kakadu National Park in Northern Territory. Important reserves exist in India and Indonesia. Protection in Australia is generally effective and dates from the early 1970s. There has been a steady increase of these crocodiles in the Bhitarkanika Wildlife Sanctuary in India from 0.87 individuals per sq. km. in 1976-77 to 3.84 sq. km. in 1992. This increase is largely due to the fact that eggs have been collected, incubated and the young reared at the research centre. As part of the crocodile conservation project in India, the Gujarat Forest Department has set up two crocodile rearing centres in Sasan and Gandhinagar. Many Estuarine Crocodiles have been bred in captivity and 857 have been reintroduced into three water bodies located in the Gir forest. Indications show that these reintroduced crocodiles have begun breeding and wild populations are increasing. The species is listed on Appendix I of CITES (the Convention on International Trade in Endangered Species) with the exception of Papua New Guinea, listed on Appendix II. In Papua New Guinea the government has made attempts to control the depletion of crocodiles by imposing size limits on skins and allowing only licensed traders to buy skins. Ranches have also been set up to breed captive crocodiles.

SPECIAL FEATURES

REFERENCES

Crocodile Specialist Group Newsletter Vol. 10 No. 4 October 1991 - December 1991.

Crocodile Specialist Group Newsletter Vol. 11 No. 2 April 1992 - June 1992.

Crocodile Specialist Group Newsletter Vol. 13 No. 1 January 1999 - March 1994.

The IUCN Amphibia - Reptilia Red Data Book Part 1 - Testudines, Crocodylia, Rhynchocephalia (1982).

Webb, G. Manolis S. and Whitford P. (1987) Wildlife Management - Crocodiles and Alligators.


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