Study of Saltwater Crocodile (Crocodilus porosus) in Mangrove forest at Sundarban in West Bengal for Conservation and Management

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1 Animal Diversity, Natural History and Conservation Vol Chapter 11 Study of Saltwater Crocodile (Crocodilus porosus) in Mangrove forest at Sundarban in West Bengal for Conservation and Management Mousumi Saha 1 *, Agniswar Sarkar 2 and B. Bandyopadhyay 1 1 Oriental Institute of Science and Technology, Vidyasagar University, Midnapore, W.B., India 2 Department of Biotechnology, The University of Burdwan, Burdwan, W.B., India ABSTRACT Sundarban is one of the world s famous biosphere reserves and heritage site located in the vast Delta of the Ganges, south of Calcutta, West Bengal, India and this is the largest and only mangrove reserve in the world inhabited by tigers. Sundarbans has extremely rich diversity of aquatic and terrestrial flora and fauna. Presently some threats have been seen for this mangrove ecosystem due to biotic pressure from the surrounding environment and, partly due to human induced or natural changes in the upper catchments. We have mainly concentrated for the management and conservation of Saltwater Crocodile (Crocodilus porosus) as these reptiles is one of most precious and valuable reptile present in Sundarbans. The saltwater crocodile is the largest of the living crocodilians, with lengths of up to 6 * Corresponding author: mou.cute@gmail.com

2 228 Animal Diversity, Natural History and Conservation Vol. 1 7m. This species is also very important for business purposes as the skins of Saltwater crocodile are considered superior to other crocodilian skins. Some study on genetic diversity of Saltwater Crocodile (Crocodilus porosus) shows that Crocodylus porosus reflects the genetic influence of other crocodilian species other than Crocodylus porosus, which may, inadvertently, have been introduced into this population prior to Second World War. These include the Siamese crocodile, Crocodylus siamensis; Philippine crocodile, Crocodylus mindorensis; and New Guineacrocodile, Crocodylus-novaeguineae. Thus to maintain the ecology of the Sundarbans and also to study every aspect of this species of crocodile it was felt necessary to initiate a project for crocodiles preservation by rearing, conserving and promoting breeding facilities. The Saltwater crocodile in general lay her eggs during May-June each year. Staffs search for the Wild Crocodile nest in the Sundarbans ending May each year, collect the eggs and maintain all the condition required for artificial hatching The rate of success of artificial hatching is nearly 60 per cent.so far a total of 332 nos of crocodile have been released in different rivers of Sundarban till This project has not just produced a large number of crocodiles, but has contributed towards conservation in a number of related fields as well. It is time to highlight and redraw attention of all concerned toward a new phase of management, keeping crocodiles as the flagship species. Thus the objective of this study is to create awareness regarding Saltwater Crocodile conservation and management and throughout the World and particularly in India and also to study the various genetic aspect regarding this Saltwater Crocodile (Crocodilus porosus). Keywords: Saltwater crocodile, Sundarban, Genetic. An Introduction About Sundarbans Sundarban is the largest contiguous mangrove area in the world and one of the World Heritage Sites of India designated by the World Heritage Convention. This biosphere reserve is located in the vast Delta of the Ganges, south of Calcutta. It is the largest and only mangrove reserve in the world inhabited by tigers. Tropical humid forest and mangroves are the major ecosystem types of the reserve. Mangrove species such as Vicennia alba, Bruguiera gymnorrhiza, Ceriops tagal and Rhizophora apiculata are the major species. Tropical semi-evergreen forest, agro-ecosystems, silviculture, pisiculture, prawn culture are the major habitats of the reserve. About 120 species of algae, 64 species of mangroves and 124 species of Angiosperms have been recorded here. Rare and endangered plant species of the reserve are Acanthus volubilis (Acanthe molle), Nypa fruiticans (Nipah palm), Sonneratia alba (Mangrove apple), Soneratia casaeolaris (Crabapple mangrove), Aegialtis rotundifolia (Nilar ixora manila), Xylocarpus granatum (Cannonball mangrove), Heritiera fomes (Sundari), Ceriops tagal (Tagal mangrove) and Lumnitzera recemosa (Sandy mangrove). There are about 163 species of birds, 40 species of mammals, 56 species of reptiles, 165 species fish, 8 species of prawn, 67 species of crab and 23 species of mollusks are reported. Animal species include Tiger, Saltwater crocodile, Fishing cat, Indian leopard cat, Yellow monitor, Olive Ridley sea turtle, Hawksbill sea turtle and Green sea turtle (Chowdhury and Ashrafi, 2008).

3 Animal Diversity, Natural History and Conservation Vol The total area of this biosphere reserve has been divided into the following interrelated zones: 1. The core zone is a compact block of reserved forest covering approximately 1,700 sq. km lying in the eastern portion of Sundarban adjoining Bangladesh border and is bound by Matla River in the west and butts into Bay of Bengal. This is a fully conserved area and it contains the Sundarban National Park and is devoted to conservation of bio-diversity, including primitive area which has remained as a central island within the reserve forests free from any external disturbances since a long time ensured through legislation. 2. Buffer zone comprises majority of mangrove areas including reserved forests areas adjoining area surrounding the above core zone and includes portion of the buffer zone of tiger reserve, Sajnakhali Wildlife Sanctuary and compact reserved forest blocks lying between Matla and Thakuran under 24- Parganas forest division. 3. Transition zone Covers the balance of the biosphere reserve area, which contains mangrove areas mostly in non-forest areas and reclaimed areas with agriculture. Area of co-operation variety of agriculture activities, stakeholders agree to work together to manage and sustainably develop area s resources for benefit of people. Area of great economic and social significance for regional development. Importance of Sundarbans Ecosystem Sundarban has extremely rich diversity of aquatic and terrestrial flora and fauna. Sundarban highly productive ecosystem acts as a natural fish nursery. Sundarban mangrove reduces the fury of cyclonic storm and prevents erosion due to tidal action. Finally, millions of people depend on Sundarban ecosystem for their livelihood and sustenance through fishing, collection of honey and fuel wood/timber (Naskar and Bakshi, 1983). Sundarban Reserved Forest The extent of mangrove reserved forest in Indian Sundarban is around 4,260 sq km, which is under jurisdiction of Chief Conservator of Forests (South), and Director, Sundarban Biosphere Reserve, and is administratively divided into Sundarban Tiger Reserve (area 2,600 sq km) and South 24 Parganas forest division (area 1,660 sq km). Out of this total recorded forest area, 55 per cent is under land vegetation cover and the remaining 45 per cent is under water body/inter-tidal zone. Field Director and Conservator of Forests is in charge of Sundarban Tiger Reserve and a Divisional Forest Officer is in-charge of South 24 Parganas forest division. Joint Director, Sundarban Biosphere Reserve and Conservator of Forests/South Circle is the direct controlling officer of DFO, South 24 Parganas division.

4 230 Animal Diversity, Natural History and Conservation Vol. 1 Nearly 40 per cent of the reserved forest area has been brought under protected area (PA) which is as follows: Sundarbans National Park (1330 sq km) Sajnekhali Wildlife Sanctuary (362 sq km). Threats in Sundarbans, West Bengal The major issues identified are: 1. Exploitation of the mangrove forests due to human pressure, 2. Conversion of mangrove areas for agricultural purposes, 3. Over-exploitation of fisheries especially for seeds of tiger prawns, 4. Loss of flora and fauna Crocodilians-all over World There are 23 living crocodilian species recognized, and they re found in over 90 of the world s countries and islands. Crocodilians are generally found in the tropical regions, being unable to survive and reproduce successfully in cold climates. However, the American alligator and Chinese alligator are the most cold-tolerant and are both found in the highest latitudes of any species. The crocodiles (colloquially called crocs), are large aquatic reptiles. Crocodiles tend to congregate in slow-moving rivers and lakes, and feed on a wide variety of living and dead mammals and fish. The larger species of crocodiles can be very dangerous to humans. The Saltwater and Nile Crocodiles are the most dangerous, killing hundreds of people each year in parts of South-East Asia and Africa. American Alligators, and possibly the endangered Black Caiman, are also dangerous to humans. Wild crocodiles are protected in many parts of the world, but they also are farmed commercially. Their hide is tanned and used to make leather goods such as shoes and handbags, whilst crocodile meat is also considered a delicacy in many parts of the world. The most commonly farmed species are the Saltwater and Nile crocodiles, while a hybrid of the Saltwater and the rare Siamese Crocodile is also bred in Asian farms (Webb and Manolis, 1993). Evolution with Phylogenetic Tree Crocodilians are a large family with a long history dating back to the Mesozoic era, million years ago. Crocodilian history is relatively well-known because their marshy habitats favor fossilization (Uriona and Farmer, 2008). Special Genetic changes of Crocodilians Today crocodilians are the most advanced of all reptiles. They have a unique combination of reptilian and mammalian/avian characteristics in fact; they are more closely related to birds than lizards.

5 Animal Diversity, Natural History and Conservation Vol Avian characteristics of Crocodilians Bird-like brain but no bladder and a reptilian digestive system. Like the birds, crocodiles have an elongate outer-ear canal, a muscular gizzard, and complete separation of the ventricles of the heart. Mammalian characteristics of Crocodilians Four chambered heart. Secondary palate is fully formed. Internal nares open in pharynx. Cochlea in internal ear. Heterodent and thecodent teeth. Diaphragm-like partition. Physical and Physiological Characteristics Skin is formed from a thick dermal layer covered with non-overlapping epidermal scales. The surface scales of each scute slough off individually rather than shedding in large patches. Adults are olive brown all over, while the lighter-colored juveniles are tan with banding on the body and tail (Thorbjarnarson, 1999). Crocodilians have strong muscles that allow the jaws to snap shut with incredible force they are capable of crushing bones, skulls, and cast iron. The teeth are conical in shape and anchored to the sockets by connective tissue, and in C. acutus there are between 66 and 68 individual teeth. They fall out throughout the lifespan and are replaced in alternate rows along the jaw. Crocodiles have no lips, meaning that they cannot close their mouths underwater. They are prevented from ingesting water, however, by a secondary palate which blocks the throat the region inside the mouth is actually still external to the body. Both salt and freshwater crocodiles, unlike alligators, have maintained salt glands on the tongue, even those that do not have contact with salt water, probably a holdover from their marine ancestry. The brain is small but complex and the senses are well adapted. They have an excellent sense of smell and a fine ability to hear. External ear openings are covered with a flap to protect the inner ear during diving. Both the eyes and nostrils are high on the head, so that they are above the water when the crocodile swims. They have moveable eyelids and a third transparent eyelid called a nicitating membrane. They apparently posses color vision but they cannot focus under water, which indicates that they use other senses when submerged. They are highly evolved predators, highly motile and metabolically efficient. They have fast reflexes and effective locomotors ability on land, where they

6 232 Animal Diversity, Natural History and Conservation Vol. 1 walk on erect legs, and in the water, where they use the long, powerful tail to swim. They move by lateral S-shaped undulations of the tail with limbs held close to the body. Their feet have unusual flexibility so the can support the crocs in various positions. They have five toes on the front feet and four on the back, all of which are partially webbed to aid in swimming. Their body systems are well adapted to the marine environment, where they attempt to maintain their body temperature within narrow limits by basking in the sun when cool and seeking shade or water when hot. Like all reptiles they are ectotherms, and do not regulate their body temperature internally. The circulatory system can divert blood away from the peripheral systems during dives or to reduce heat loss. They have well-evolved metabolisms that use and store nearly the entirety of a meal. Because of this they ingest no more than 50 full meals a year and a large crocodile can last a year without eating (Grigg et al., 1993). Life Cycle of Crocodiles A crocodile s life begins in the egg, buried with a clutch on the banks of a river or lake. Crocodiles lay eggs that are less brittle than bird eggs and bury them in mounds of rubbish and vegetation or sand. The extent of parental care is varied many females guard the nest assiduously, fasting until they hear the grunts of the young, and then dig them out, even cracking the eggs to release the hatchlings. Between 90 and 100 days after being laid the eggs hatch, right at the beginning of the rainy season. Beyond one meter in length, mortality of crocodiles decreases. They have few natural predators, especially if they can avoid being caught on land, although occasionally sub adult animals can be killed by snakes or large predators such as leopards. Females grow more slowly and reach maturity at a smaller size than males, who continue growing and usually exceed females in maximum size. Crocodilians can be long lived in the wild and there are records of particular individuals residing for decades They will spend much of their time basking in the sun and hunting; feeding is lowest in the cool periods of winter but increases with temperature during the spring and summer months. Females reach sexual maturity at lengths of 2.5 meters, regardless of age. When the mating season begins, an extended courtship period can last up to two months. When it becomes time for the female to nest, she must be extremely careful in selecting the site. Nest mortality is high; even during the dry season, flooding can kill an entire clutch, especially in hole nests which can fall below the water level during periods of heavy rains. Eggs require oxygen diffusion through the porous shell, so many can asphyxiate under imperfect conditions. Likewise, although many crocodiles guard the nest assiduously, predation is common among crocodile clutches.

7 Animal Diversity, Natural History and Conservation Vol Reproduction Small mammals, fungus, insects, and reptiles all dig out and consume the eggs. If the female can successfully protect her nest to the hatch, another cycle of crocodile life can begin. Mating takes place in the water and the mother then lays between 20 and 80 eggs on a hard nesting area on the shore. Incubation takes up to 3 months and the nest is guarded fiercely by the female. The hatchlings are oviporous, meaning they are perfectly formed, but stay with their mother for 3 years before they are weaned. Sexual maturity is reached at a certain length anywhere from 5 to 15 years of age. Crocodilian Habitat Requirements Diet Crocodiles require hundreds of kilometers of undisturbed wetlands and large shallow bodies of water such as slow rivers, swamps, and marshes, because they require such a large territory for each individual. Crocodiles avoid strong wind and wave action because they require calm water to swim effectively. It is theorized that the still water allows them to keep only the nostrils above water, but if it is windy the snout must be raised at a steeper angle. This makes it more difficult to swim. The crocodiles need protected waters and will avoid the open water if it is rough. This means that tree cover is important and deforestation can disturb their habitats even if water quality is preserved. Crocodiles are carnivores. Their diet depends on their size and what is available around them. Hatchlings and young animals eat insects, snails, small fish and crustaceans. They grow fast and must eat often. As they grow larger, their prey and time between meals does also. They go from eating large fish and reptiles to mammals of all size, monkeys and buffalo to zebras and snakes. They generally eat the larger mammals as they come to the water to drink or cross rivers, during the dry season or migration. Since this is seasonal, crocodiles eat large amounts and can go for a year between meals. The crocs teeth are big and sharp, but are not used to chew. Instead they use them for snatching and grasping prey, which is then taken under and drowned (Garrick and Lang, 1977). Sex of Chromosome Sex of the crocodiles is determined on the basis of the temperature during hatching. At low temperature hatchlings become female and at high temperature they come out as male. Crocodylus porosus (Saltwater Crocodile) The Estuarine crocodile or Saltwater Crocodile is found in the Gangetic delta of Sunderban estuary in good numbers. Artificial hatching and rearing had been initiated. The Sunderbans estuary covers an area of 4389 sq.km and forms suitable

8 234 Animal Diversity, Natural History and Conservation Vol. 1 natural haunt for estuarine crocodile. This species in the past was in abundance in the mangrove forests, but for the value of its skin, were mercilessly killed to such an extent as to threaten the species with extinction (Messel and Vorlicek, 1989). Ecology and Natural History The saltwater crocodile is the largest of the living crocodilians, with reported lengths of up to 6 7m. Noted for its large size and fierce disposition, the saltwater crocodile has a reputation as a man-eater. Females become mature at lengths of approximately m (about 12 years of age) and make mound nests during the annual rainy period.clutch size is typically and incubation normally lasts some 90 days. Nesting is a wet season activity and in northern Australia loss of nests due to flooding is very high. Nest predators include monitor lizards and humans. Appearance Saltwater crocodile is a large-headed species with a heavy set of jaws. A pair of ridges runs from the eye orbits along the centre of the snout. Scales are more oval in shape than other species, and scutes are relatively small. Juveniles are pale yellow in colour with black stripes and spots on the body and tail. The juvenile coloration persists for several years, growing progressively paler and less colourful with more indistinct bands which eventually disappear. 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 that tends to be 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 (Tisdell et al., 2005). 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, with only the smaller items taken less frequently. Prey items include crustaceans and vertebrates (e.g. turtles, snakes, shore and wading birds, buffalo and domestic livestock, wild boar, monkeys) (Webb et al., 1991). Habitat Saltwater crocodiles are distributed throughout the coastal regions of northern Australia, from Broome in Western Australia to Rockhampton in Queensland. It is found primarily along mangrove-lined tidal rivers (in brackish water) up to 200 km from the coast, and flood plain billabongs, creeks and freshwater swamps up to 100 km from the coast. Adults can venture out to sea and swim around coastlines or between islands. Individuals have been found to travel over 1000 km by sea. Saltwater crocodiles are found in higher densities in areas with a good food supply and abundant nesting areas, where recruitment into the population is higher (Magnusson, 1980).

9 Animal Diversity, Natural History and Conservation Vol Behaviour Most of their time is spent thermo regulating, to maintain a body temperature between 30 and 32 degrees Celsius (the optimum temperate for digestion and other activities), and in maintaining their territories. Territorial behaviour relies upon a number of subtle cues, such as changes in body posture and low-frequency vocalisation. Violence is generally avoided, as serious injuries and death can occur in larger animals. Nesting Saltwater crocodiles are mound nesters, using a variety of grasses and other materials. By creating a mound, the eggs are raised about the ground water table, and the risk of flooding is slightly diminished. Yet, many nests are lost to flooding each year. When the eggs are submerged, oxygen cannot reach the embryos and they die within a few hours. Other major causes of death are overheating (temperatures rising above 34 degrees C) and predation by goannas/monitors and feral pigs. Nesting sites near water are selected, so the females can remain on guard, and so the hatchlings do not have far to travel. Courtship occurs in September and October, and nesting takes place throughout the wet season, generally between November and March. The female remains close to the nest throughout incubation and defends it vigorously against any potential threat. Once the eggs start to hatch, the hatchlings produce characteristic calls which stimulate the female to begin digging the nest open. She carries hatchlings to the water in her mouth, gently breaking open unhatched eggs. Juveniles remain close to the female for several months after hatching in a creche, staying in touch with acoustic calls. On average, at least 80 per cent of all eggs die during incubation, and less than one percent of all hatchlings will reach maturity. Major predators of the hatchlings include birds and fish, but the major cause of death is cannibalism by other, adult crocodiles (Deraniyagala, 1937). Sex of Saltwater Crocodiles The embryos do not have sex chromosomes, and sex is not determined genetically. Rather, sex is determined by temperature mostly males are produced at around 31.6 degrees C, and females produced at slightly lower or higher temperatures (Webb et al., 1983). Saltwater Crocodile in Sundarban, India To study how conservation and management of Saltwater Crocodile is done in Sundarban we conducted a tour. During this trip we where able to visit several places and tiger reserves like Sajnekhali Tiger Reserve, Dobanki Tiger Reserve and Sudhanyakhali Tiger Reserve. In Sajnekhali Tiger Reserve we have seen a museum, which provided us a lots of information about Sundarbans and its flora and fauna, Crocodile Pond, Artificial Hatching Ground of Sea Turtle, Watch Tower, Endangered

10 236 Animal Diversity, Natural History and Conservation Vol. 1 Mangrove Propagation Centre and various types of plant like Hetal, Sundari, Goran etc. In Dobanki we have not only seen Tiger Reserve but also Deer park. Among this entire various conservation project we had focused on the Crocodile Conservation. In India, the estuarine crocodile is restricted in its distribution to the tidal estuaries, marine swamps, coastal brackish water lakes and lower reaches of the larger rivers. The saltwater crocodile has a vast geographical range that extends from Cochin on the west coast of India to the Sunderbans in West Bengal and to the Andaman Islands. Single individuals can be found some distance from their usual range as they can travel long distances (over a thousand km) by sea. Barnacles have been found on the scales of a few stray individuals. This sea-faring ability probably helps to explain their wide distribution. The species is seriously endangered, from hunting and now largely from loss of habitat, particularly breeding sites. To maintain the ecology of the Sunderbans it was felt necessary to initiate a project for crocodiles within its natural home for preservation by rearing, conserving and promoting breeding facilities. Bhagabatpur Crocodile Project situated in 24- Parganas Division started functioning since Crocodilians Pollution Today Saltwater crocodiles are in danger of becoming extinct. One reason is that many are killed each year for sport or for their skins, which are used to make purses, shoes and belts. These approaches of human being towards crocodilians are causing pollution within their species and habitat. Thus conservation of saltwater crocodile is a most important ecological conservation work (Bustard and Choudhuri, 1980). Conservation of Saltwater Crocodile The estuarine crocodile in general lay her eggs during May-June each year. Staffs search for the Wild Crocodile nest in the Sunderbans ending May each year. After a nest has been located, the eggs are collected carefully by hand and kept in wooden box filled with artificially made nest building materials after making the top and direction with the help of hard compass on each egg. If the eggs are turned or jarred, the delicate embryo is likely to die. Care is taken to collect eggs during the cool part of the day as drastic temperature change would be harmful. The eggs are placed in the artificially made nest in specially made hatchery at Bhagabatpur fully covered by wire-mesh. The only access to this enclosure is through the trap door on the roof. A steady temperature of 30-50C is maintained inside the nest. The rate of success of artificial hatching is nearly 60 per cent.so far a total of 332 nos of crocodile have been released in different rivers of Sunderban till After hatching the juvenile are kept in a protected area known as Crocodile Pond

11 Animal Diversity, Natural History and Conservation Vol In Sajnekhali Crocodile Pond has been Constructed to Protect Saltwater Crocodile

12 238 Animal Diversity, Natural History and Conservation Vol. 1 This way In Sundarban Crocodile has been conserved, but for further success modern day biotechnological tool must be used. So that this details information about this species of crocodile can be obtained and much more work can be done. References Bustard, H.R. and B.C. Choudhuri (1980). Conservation future of the saltwater crocodile (Crocodylus porosus Schneider) in India. J. Bombay Nat. Hist. Soc., 77 (2): Chowdhury, M. T. A. and S. A. Ashrafi (2008). Environmental factors determining forest resources used in livelihood of the peripheral villages of Sundarbans. J. Innov. Dev. Strategy, 2(2): Deraniyagala, P.E.P. (1937). The nest-guarding habit of the estuarine crocodile of Ceylon. Ceylon Journal of Science, 20 (2): Garrick, L.D., and J.W. Lang (1977). Social signals and behaviors of adult alligators and crocodiles. American Zoologist, 17: Grigg, Gordon and Gans, Carl (1993). Morphology and Physiology of the Crocodylia, in Fauna of Australia. Amphibia and Reptilia, Australian Government Publishing Service, Canberra, Vol 2A, chapter 40, pages Magnusson, W.E. (1980). Habitat required for nesting by Crocodylus porosus (Reptilia: Crocodilidae) in northern Australia. Aust. Wildl. Res., 7: Messel, H, and Vorlicek, GC (1989). Ecology of Crocodylus porosus in northern Australia. In: Crocodiles. Their Ecology, Management and Conservation. A Special Publication of the IUCN/SSC Crocodile Specialist Group, IUCN, Gland, Switzerland, pp Naskar, K. and Guha Bakshi, D. (1983). A brief review on some less familiar plants of the Sundarbans India. Journal of Economic and Taxonomic Botany, 4(3): Thorbjarnarson, J. (1999). Crocodile Tears and Skins: International Trade, Economic Constraints, and Limits to the Sustainable Use of Crocodilians. Conservation Biology, 13(3), Tisdell, C.A. Swarna Nantha and Wilson, C. (2005). Australian tropical reptile species: ecological status, public valuation, attitudes to their conservation and commercial use. in A.R. Burk (ed.) Trends in Biodiversity Research, Nova Science Publishers, New York, pp Uriona T.J. and Farmer C.G. (2008). Recruitment of the diaphragmaticus, ischiopubis and other respiratory muscles to control pitch and roll in the American alligator (Alligator mississippiensis). Journal of Experimental Biology, 211: Webb, G.J.W., Hollis, G.J. and Manolis, S.C. (1991). Feeding, growth, and food conversion rates of wild juvenile saltwater crocodiles (Crocodylus porosus). J. Herpetology,25(4):

13 Animal Diversity, Natural History and Conservation Vol Webb, G.J.W. and Manolis, S.C. (1993). Conserving Australia s crocodiles through commercial incentives. In: Herpetology in Australia, (ed. by D. Lunney and D. Ayers) Surrey Beatty, Sydney, pp Webb, G.J.W., Sack, G.S., Buckworth, R. and Manolis, S.C. (1983). An examination of Crocodylus porosus nests in two northern Australian freshwater swamps, with an analysis of embryo egg mortality. Aust. Wildl. Res., 10:

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