The Pig-nosed Turtle

Photo: John Cann

Table of Contents

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Summary

Taxonomy

Description

Distribution

Population Status

Habitat and Ecology

Threats to Survival

Conservation Measures Taken

Conservation Measures Proposed

Captive Husbandry

Current Research

Literature Cited

Source

Summary

Carettochelys insculpta is the sole surviving member of the Carettochelydidae, a family of turtles widely distributed during the Tertiary. It is restricted to the southern rivers of New Guinea and the major rivers of the Northern Territory in Australia. Carettochelys is therefore a distinctive geographic and taxonomic relict and, although locally abundant, it is rare in the sense of being geographically restricted.

Populations in New Guinea are thought to be declining because of increased exploitation for meat and eggs. This exploitation has been exacerbated in recent times by the introduction of modern technology, principally outboard motors. In addition, clan warfare has ceased, and people have moved from the hinterland to more convenient positions along river banks. Moreover, levels of industrial activity such as mining and exploration for oil, gold and copper, logging and fishing have increased in recent times. The activities of any one of these has the potential to impact on wildlife populations including those of the pig-nosed turtle.

In Australia, feral water buffalo pose a major threat through trampling of nesting banks and widespread destruction of the riparian vegetation upon which the turtles depend. Other potential pressures include aggressive pastoral and agricultural practices that push the land in the important catchments beyond land capability, with resulting erosion, destruction of riparian vegetation, and siltation of water courses. Mining activity in sensitive areas such Kakadu National Park, may also pose a threat unless strict controls are applied on containment of mine waste, fishing activities of the mine staff, drawdown of the water table and routes taken in the transport of chemicals used for extraction of minerals.

Urgent research is required to determine trends in population numbers and levels of exploitation in New Guinea. Additional research should be undertaken to determine whether management leading to sustainable exploitation of Carettochelys is necessary and attainable, and to make recommendations on how such sustainable utilization might be brought about. Associated research should be directed at integrating into local economies, the measures designed to ensure a sustainable harvest.

In Australia, research is required to determine the distribution of Carettochelys so that the value of the two known major populations can be adequately assessed. Wet-season habitat requirements, extent of seasonal movements and requirements of juveniles are unknown, yet this information is needed to gauge the possible impact of proposed or potential development within catchments and to gauge the adequacy of existing reserves for protecting the species.

Taxonomy

Carettochelys insculpta was first described as a new genus and species in 1886 by Dr E.P. Ramsay from an incomplete specimen collected in the Strickland River, a tributary of the Fly River in Papua New Guinea. The circumstances of its collection, by Walter Froggatt and Jas H. Shaw while on an expedition with the Geographical Society of Australasia, are described by Waite (1905). The genus is monotypic and no subspecies are recognized.

Soon after its description, Boulenger (1887) placed Carettochelys insculpta in its own family, the Carettochelydidae, and included it among the sub-order of side-necked turtles, the Pleurodira. He made this latter decision with some reference to morphological characters, but primarily because at the time, only side-necked turtles were known from Australia and New Guinea. Baur (1891) was vehemently opposed to grouping Carettochelys with the side-necked turtles, and called upon Ramsay to release details of the articulation of the cervical vertebrae "to show at once the affinities of this peculiar genus". Unfortunately, the specimen lacked key anatomical elements, the cervical vertebrae, so the matter remained one of considerable debate (Strauch, 1890; Vaillant, 1894; Boulenger, 1898; Gadow, 1901; Ogilby, 1907; Hay, 1908) until the work of Waite (1905) became widely known. He described a more complete specimen from the island of Kiwai at the mouth of the Fly River, and examination of the cervical vertebrae established that Carettochelys insculpta properly belongs in the sub-order Cryptodira, not the side-necked Pleurodira.

The debate on the affinities of Carettochelys continued sporadically, as summarized by Walther (1922:609-610), Frair (1985) and Meylan (1988). Current wisdom has it that Carettochelys insculpta is the sole surviving member of a family that was widespread in the late Tertiary (Pritchard, 1979a), with closest living relatives among the soft-shelled turtles (Trionychidae) (Chen et al., 1980; Frair, 1983, 1985). However it is sufficiently distinct to warrant retention of the family Carettochelydidae and some would argue that it should be separated from the Trionychids at the level of superfamily at least (Williams, 1950; Frair, 1985). Time of divergence is estimated from the molecular clock to be of the order of 40 million years (Chen et al., 1980).

Description

Original detailed descriptions of the morphology of Carettochelys insculpta are provided by Ramsay (1886), Waite (1905) and Walther (1922) and are summarized by Cogger (1975) and Pritchard (1979a). Carettochelys insculpta is a heavy bodied turtle, up to 22.5 kg in weight and 56.3 cm in length (Rose, unpublished data). Colouration is rich grey, olive-grey or grey-brown above and white, cream or yellowish below. The jaws are cream and there is a pale streak behind the eye. The species is cryptodirous, that is, the vertebral column in its neck flexes in the vertical plane when the head is withdrawn. There are no epidermal scutes overlying the shell, which is covered instead with a continuous skin. The carapace is relatively deep, with a median keel toward the rear. The peripheral bones are complete and well-developed, so there is no flexible shell margin. The plastron, although small, forms a continuous plate without even a median fontanelle. Several of the plastron elements are not rigidly ossified together, but rather have cartilaginous connections which allow a certain amount of flexibility. The limbs are paddle-shaped, like those of sea turtles, each with two claws. The dorsal surface of the tail is covered with a single line of crescent-shaped scales which decrease in size from the base to the tip. Prominent folds of skin extend laterally on each side from the undersurface of the tail across the thigh region and down the hind limbs. The nostrils are at the end of a prominent fleshy proboscis. Mature males can be distinguished from females of the same size by the tail which is larger in males to enable successful copulation.

On emergence, hatchlings have well formed strong limbs but an extremely soft plastron and carapace. The plastron has a deep crease where folding of the body has occurred during incubation. The periphery of the shell comprises loose flaps of skin, which become firm after about one week to form a serrated margin. Hatchlings also have a tuberculate median keel; a poorly defined and transient polygonal outline around each of these tubercules may be homologous to the scute seams of other turtles (Pritchard, 1979a). The tubercules are lost as the turtle grows and the median keel is present only on the posterior quarter of the carapace by the time the turtle matures.

Hatchlings from New Guinea weigh 29.6 +/- 0.32 g on average and have an average carapace length of 53 +/- 0.25 mm (Rose, unpublished data), whereas the equivalent data for the South Alligator River are 24.7 +/- 0.84g and 56.1 +/- 0.91 mm (Georges and Kennett, 1989) and for the Daly River are 20.5g and 41.1 +/- 1.22 mm (Webb et al., 1986). They exhibit the full range of shell colour variation shown in the adults, even within single clutches, and the pale streak behind the eye is present. There may be small light patches on the carapace radiating to the peripherals, and these are more prominent toward the rear of the carapace.

Distribution

The discovery and description of this peculiar species (Ramsay, 1886) generated great interest in Europe (Walther, 1922), and the species was often specifically sought by explorers and travellers visiting Papua New Guinea and Irian Jaya (Boulenger, 1914; de Rooij, 1915, 1922; Wermuth, 1963; Schultze-Westrum, 1963; Cann, 1974). The species was soon recorded from the Strickland (Ramsay, 1886; Waite, 1905), Fly (Boulenger, 1898; Waite, 1905), Morehead (Longman, 1913), Aramia, Omati (Slater, 1961), Binaturi (Rhodin and Rhodin, 1977), Purari (Pernetta and Burgin, 1980) and Kikori Rivers (Rose, 1981) of Papua New Guinea. It is known in Irian Jaya from the Setekwa (Boulenger, 1914), Heron (de Rooy, 1922) and other southern flowing rivers (Cann, 1974, 1978, 1980). It was also reported from Lake Jamur (de Rooij, 1915), but the specimen consisted of fragments of shell and may have been carried there by natives (de Rooy, 1922). Brongersma (1958) reports that Carettochelys is relatively common in the southern flowing rivers of New Guinea and Lake Jamur. It seems likely that Carettochelys insculpta occurs in all of the major and some of the smaller southern-flowing rivers of Papua New Guinea and Irian Jaya, but the exact boundaries to its distribution are unknown. No published records of the species exist for rivers east of the Purari, but local native information (Rose, unpublished) indicates that its range extends to the Vailala River in the east.

The existence of Carettochelys insculpta in northern Australia was not widely known until a specimen from the Daly River was reported in the scientific literature (Cogger, 1970; Peters, 1970). Evidence of breeding in Australia dates back to 1918 when eggs from the East Alligator River were lodged with the Victorian Museum (Georges et al., 1989) and the presence of Aboriginal rock paintings of Carettochelys (Cann, 1980; Dupe, 1980; Georges, 1987), some dating back more than 7000 years (George Chaloupka, pers. comm.) suggest that the species has been a long term resident of northern Australia. Nevertheless, Cogger and Heatwole (1981) have argued that the restricted range of Carettochelys (New Guinea and scattered coastal localities in the Northern Territory), the lack of even sub-specific differentiation between the two areas, and the highly aquatic nature and estuarine tendencies of this species, suggests that it is a relatively recent immigrant from New Guinea to Australia.

In northern Australia, Carettochelys insculpta occurs in the Daly (Cogger, 1970; Cann, 1972; Webb et al., 1986; Georges, 1987), South Alligator (Schodde et al., 1972; Legler, 1980, 1982; Press, 1986), East Alligator (Georges et al., 1989) and Victoria drainages (Cogger, 1975; Jessie Roberts, pers. comm.) There have also been anecdotal reports of the species from the Darwin, Adelaide, McKinlay and Roper Rivers of the Northern Territory (Cann, 1972; John Bywater, pers, comm.) and the Wenlock River on the west coast of Cape York (Keith Day in pers. comm. with Webb et al., 1986). The distribution of Carettochelys in Australia clearly requires further investigation.

Population Status

Carettochelys insculpta was long considered one of the rarest turtles in the world (Groombridge, 1982) but it is not certain whether this reputation reflects its remote distribution or also low population densities (Pritchard, 1979a). In fact many consider it to be fairly common where it occurs in both Australia and New Guinea (Brongersma, 1958; Slater, 1961; Cann, 1974, 1980; Press, 1986; Shelley Burgin, pers. comm.), but there are few precise estimates of population sizes. Georges and Kennett (1989) found Carettochelys to be widespread between the tidal reaches and the head-waters of the South Alligator River in Australia, and that high densities may be present in the upper reaches during the dry season (33.8 +/- 11.3 turtles per ha in small discrete ponds on the main channel). Populations of Carettochelys in the Kikori River District of Papua New Guinea (Gulf Province) are reported to have been severely depleted in the last 20 years, and the populations in the Western Province appear to be declining (Rose, 1981; Groombridge, 1982). It is reported as rare in Irian Jaya, with a sparse and limited distribution (Anon., 1978), but this conflicts with the observations of Cann (1974, 1978, 1980). Regardless of high densities in some areas within its range, Carettochelys is both a geographic and a taxonomic relict species (sensu Simpson, 1944) and is rare in the sense of being geographically restricted. Locally abundant species with restricted ranges are possibly more vulnerable than scarce but widely distributed species.

Habitat and Ecology

In Papua New Guinea, Carettochelys insculpta inhabits rivers (including estuarine reaches and river deltas), grassy lagoons, swamps, lakes and water-holes of the southern lowlands (Leim and Haines, 1977; Groombridge, 1982). Locals of the Purari region claim that the hatchling turtles congregate in the lower delta and feed on vegetation and fruits of mangroves. In Australia, there are no substantiated reports of Carettochelys insculpta occurring in estuarine areas (Press, 1986; Georges and Kennett, 1989) but it is known from the clear, shallow, continuously-flowing waters of the Daly drainage (Cogger, 1970; Cann, 1972; Webb et al., 1986) and from lowland billabongs, upland billabongs and plunge pools of the Alligator Rivers region (Legler, 1980, 1982; Press, 1986; Georges and Kennett, 1989). The preferred dry season habitat in the Alligator Rivers region is typified by Barramundi Creek (Legler, 1982) and Pul Pul Billabong (Georges and Kennett, 1989). Average depth was approximately 2 m but there were holes between 3 and 7 m deep. The substratum was sand and gravel covered with a thin layer of fine silt and litter. Fallen trees and branches, undercut banks, exposed tree roots, and local accumulations of litter provided a diverse range of underwater cover for turtles. The banks of the billabongs were covered in a dense broadleafed forest, including the important turtle food Ficus racemosa. The many small sandbanks adjacent to the water were more than adequate in number and size for nesting. Water flows through the billabongs in all months of most years.

Carettochelys is omnivorous, but tending more toward herbivory than toward omnivory (Groombridge, 1982). In the Gulf Province of Papua New Guinea, it principally feeds on the unripe fruits of the mangrove species Sonneratia spp. possibly by cropping the fruits from the vegetation at high tide (Rose, unpublished data). Fruits from Xylocarpus sp., Nypa fructicous, Canorium indicum, Antrocarpus incisor, the wild pit pit Sachhorum robistum are also eaten. Animal foods included the molluscs Batissa violocea, Nerita sp and Centhidea sp, and the crustacean Siyellu serrata. In Australia, Carettochelys feeds on the leaves, fruits and flowers of riparian vegetation, especially the Fig Ficus racemosa, the bush apple Syzygium forte, and Pandanus aquaticus (Schodde et al., 1972; Legler, 1982; Georges and Kennett, 1989). Other foods include aquatic insect larvae, crustacea, mollusca, fishes and mammals possibly eaten as carrion, and aquatic plants such as algae, Vallisneria sp. and Najas tenuifolia (Cogger, 1970; Schodde et al., 1972; Legler, 1982; Georges et al., 1989; Georges and Kennett, 1989). The wide range of foods eaten provides great scope for opportunism, and the diet varies greatly with the foods available from locality to locality.

In New Guinea, Carettochelys insculpta nests in the late dry season between September and December (Cogger, 1975; Cann, 1978; Pernetta and Burgin, 1980), but as eggs appear in the Kikori markets as late as February (Groombridge, 1982), the nesting season may extend to the end of January. Nesting in the Kikori District spanned 19 weeks in 1981/82 (Rose, unpublished data). Carettochelys also nests in the late dry season in Australia. The nesting season on the Daly River extends between mid August and early October, (Georges and Kennett, 1989). Nesting is more protracted in the Alligator Rivers region ranging from mid July to early November (Georges and Kennett, 1989). Bimodal distributions of nesting dates both in the Kikori District of Papua New Guinea and the Daly River of Australia provides strong evidence of multiple clutching (see also Legler, 1980), a conclusion supported by examination of reproductive tracts of three specimens dissected during the nesting season at Kikori (Rose, unpublished data).

Carettochelys typically chooses clean fine sand adjacent to water in which to nest (Cann, 1978, Pernetta and Burgin, 1980; Legler, 1982; Webb et al., 1986; Rose, pers. obs.), but also nests in mud and loams at some localities (Slater, 1961; Cogger, 1975: Plate 59 and pers. comm.; Groombridge, 1982; Rob Elvish, pers. comm.; Rose, pers. obs.) It nests upon sand banks adjacent to water in the middle reaches and mouths of rivers, on sandy shores of islands in river deltas, and on coastal beaches (Rhodin and Rhodin, 1977; Groombridge 1982; Webb et al. 1986; Georges and Kennett 1989). Nesting activity has been reported from the Strickland, Setekwa, Purari, Kikori, Turama, Era, Pai and Fly Rivers of Papua New Guinea (Waite, 1905; Boulenger, 1914; Pernetta and Burgin, 1980; Rose, unpublished data), the southern rivers of Irian Jaya (Cann, 1978, 1980), and the Daly, South Alligator and East Alligator Rivers of northern Australia (Schodde et al., 1986; Georges et al., 1989; Georges and Kennett, 1989).

The eggs are white, hard-shelled and almost quite round (Ramsay, 1886) with a mean diameter of 38.7 +/- 1.3 mm and a mean weight of 33.7 +/- 3.5 g for eggs from the Daly River of northern Australia (Webb et al., 1986). Eggs from the East Alligator River were somewhat larger (42.0-44.8 mm, n=15) (Georges et al., 1989), more in keeping with the size of eggs in New Guinea (Purari River: 38-46 mm, mean 42.9 mm, n=108, Pernetta and Burgin, 1980; Kikori River: means 42.8 +/- 2.3 mm, 45.7 +/- 0.7 g, Rose, unpublished data). Both the ultrastructure (Erben, 1970) and the gross morphology of the eggshell (Webb et al., 1986) have been described, and Webb et al. provide details on egg constituents.

Clutch sizes range from 7 to 19 in the Daly River of northern Australia (Webb et al., 1986; Georges, 1987) and from 8 to 39 in New Guinea (De Rooij, 1915, Cann, 1978; Pernetta and Burgin, 1980; Groombridge, 1982; Rose, unpublished). Some of the largest clutches may have been laid by more than one female, in areas where there was intense nesting activity (Cann, 1978). Nests of Carettochelys insculpta are recorded as being subject to predation by monitor lizards (Pernetta and Burgin, 1980; Legler, 1982; Georges and Kennett, 1989) and man (Cann, 1974; Pernetta and Burgin, 1980; Groombridge, 1982; Press, 1986; Georges and Kennett, 1988). Those that survive require 64 to 74 days (at 30oC) to develop to a point where hatching is possible (i.e. until yolk internalization) after which they enter an embryonic aestivation within the egg (Webb et al., 1986). At onset of aestivation, metabolic rate decreases precipitously and embryonic growth ceases. Yolk is used during diapause at a rate that yielded an estimate of 59 days to yolk exhaustion at 28oC to 30oC Webb et al., 1986). Hatching can be stimulated by reducing oxygen availability, either by submerging eggs in water or replacing the atmosphere that surrounds them with nitrogen, suggesting that in the field, hatching is either stimulated by early season rains or flooding (Webb et al., 1986; Georges, in prep). Incubation period for 30 natural nests from the Kikori River of Papua New Guinea was between 86 and 102 days (average nest temperature 31.6oC ) (Rose, unpublished data). This presumably included a substantial period of aestivation, which would account for the discrepancy between these findings and those of Webb et al. (1986).

The hatchling sex ratio of Carettochelys insculpta is influenced by the temperature that prevails during incubation, both under constant conditions in the laboratory (Webb et al., 1986) and under fluctuating conditions in field nests (Georges, 1987; Georges, submitted). Embryos incubated at a constant 28oC and 30oC become males whereas those incubated at 32oC become females (Webb et al., 1986). The laboratory threshold for sex determination is not known precisely (between 30 and 32oC Webb et al., 1986), but under field conditions, the threshold of 31.6oC (Georges, 1987) agrees very well with the average nest temperature in New Guinea of 31.6oC (Rose, unpublished data).

There is little information on natural levels of survivorship (83.2% from 30 nests, Rose unpublished data) and none on rates of recruitment to the parent population, nor is it known how long the young turtles take to reach maturity.

Threats to Survival

Carettochelys insculpta is highly prized as a food item by the indigenous peoples within its range both in Australia and New Guinea (Schultze-Westrum, 1963; Cann, 1980; Press, 1986) and it is important to the subsistence economies of several Papua communities (Pernetta and Burgin, 1980). Both the adults and their eggs are collected, consumed and sold throughout its range in Papua New Guinea. In Kikori Market alone, over 5000 eggs were sold between October 1980 and February 1981 (Groombridge, 1982). In the following year, over 20,000 eggs were collected and consumed in Kikori and three surrounding villages (Rose, unpublished data). In the breeding season, villagers collect female turtles and their eggs when they come to shore to nest, or they locate nests by systematically prodding sand banks with a stick or spear. In some areas, pit-traps are checked each day for nesting turtles that have fallen in to them on the previous night (Groombridge, 1982). Out of season, the turtles are caught by hand from boats in shallow water and swamps, or are caught on lines baited with crab or de-shelled mussels (Groombridge, 1982) and in basket traps (Schultze-Westrum, 1963).

In northern Australia, turtles are regularly eaten by Aborigines, and Carettochelys insculpta are favoured by some for their size and flavour (Cann, 1980; Press, 1986). Traditionally, men used to climb trees on the banks of billabongs and spear the turtles when they came near to the surface (Georges, 1987). Alternatively, Carettochelys could be hunted by diving on top of them from the bank or by waiting quietly in the water while others herded the turtles in. Today, however, they are more often caught on hand lines baited with wallaby or buffalo meat (Cann, 1972; Georges, 1987). There are no reports of Australian Aborigines harvesting the eggs of Carettochelys.

Groombridge (1982) considers that traditional hunting of turtles and harvesting of eggs in southern New Guinea is the principal threat to the species. Stereotyped nesting habits render Carettochelys insculpta (like sea turtles) extremely susceptible to over-exploitation. Levels of exploitation in the Gulf and Western Provinces have been exacerbated in recent times by the introduction of modern technology, principally outboard motors, and because since clan warfare has ceased, people have moved from the hinterland to more convenient positions along the river banks. Populations in New Guinea have been reported to have declined sharply in the past 20 years (Groombridge, 1982). There are few data on levels of exploitation in Australia. Georges & Kennett (1988) report an annual offtake of 19 turtles by two Aboriginal families at Nourlangie Camp, but without adequate data on population numbers and recruitment, it is not known whether this exceeds a sustainable yield.

Feral water buffalo pose a major threat to pig-nosed turtles and their habitat in the Alligator Rivers region of Northern Australia. The sand banks used for nesting by Carettochelys are also used as easy access to water and as resting places at night by water buffalo. This led Archie Carr to comment in a letter to Pritchard (1979b) that Carettochelys may have become much more restricted in its Australian distribution since the introduction of water buffalo. In 1987, buffalo densities in Goodparla Station (now part of Kakadu National Park) were so high that all potential nesting banks were heavily trampled. Such trampling is known to destroy nests (Georges & Kennett, 1989).Water Buffalo also destroy the riparian vegetation, upon which the turtles depend in the dry season for food, by foraging on young plants and by structurally destroying the banks of billabongs. While this may initially benefit Carettochelys by increasing underwater cover afforded by fallen trees, branches and litter, it can only have long-term deleterious effects on the turtle populations.

Agricultural and pastoral activities in the catchments of the Daly drainage have the potential to seriously impact Carettochelys populations where stocking rates are high, the riparian vegetation is cleared, or the land is pushed beyond its capability, with subsequent erosion and siltation of water courses.

Mining activity in sensitive areas such as Kakadu National Park, may pose a potential threat to the environment and the fauna that depends upon it (Dames and Moore, 1987; Georges and Kennett, 1988). Exploration and Mining for gold by chemical extraction is planned for the head-waters of the South Alligator River, in the region identified as providing important refuge ponds for Carettochelys in the dry season (Georges and Kennett, 1988, 1989). Contaminated rainwater run-off, accidental discharges from the tailings dam or treatment plant, or accidental spillage of hazardous industrial chemicals at stream or tributary crossings during transport to the mill site are all potential sources of destructive pollution of the South Alligator River. Demands on water for mining operations may deplete the water table and reduce water levels in the shallow billabongs used by Carettochelys as dry-season refuges. Upgrading river crossings and causeways may restrict the free movement of turtles during the early dry-season Carettochelys is easily caught on baited lines (Cogger, 1970; Georges and Kennett, 1988). Populations may be decimated by increased fishing activity in the dry-season refuges by mine workers and others allowed into the mining area. Although fishing may be prohibited for non-aboriginal employees of the mine, any restrictions will be difficult to apply to Aboriginal employees (to be a substantial proportion) and those who accompany them, as the Aboriginal community remains the traditional owner of the head-waters of the South Alligator River.

The issue of allowing mining and extensive exploration with Kakadu National Park has not been resolved at the time of writing, and the atmosphere of confrontation is not conducive to finding a compromise that serves both the long-term interests of the unique biota of the region and the interests of a sustainable Australian economy (Georges, 1990a,b).

Similar concerns are felt for New Guinea populations. Gold and copper are being mined on the Fly river at Ok Tedi and standards for the protection of the environment there have been questioned (Georges, 1990b). Quite apart from the risk of environmental contamination, mining and other commercial operations organized by expatrial interests will increase river traffic which will in turn increase the number of turtles and eggs taken.

Conservation Measures Taken

There have been several calls for Carettochelys to be given a high priority in conservation funding. In view of its restricted range and its importance to the subsistence economy of many native peoples in Papua New Guinea , Pernetta and Burgin (1980) recommend that investigation of the biology and population status of Carettochelys be given high priority. Groombridge (1982) recommended that studies of the biology and distribution of the species in Papua New Guinea and Australia, and of the distribution, population status and levels of exploitation in Irian Jaya, be undertaken. He signaled that the IUCN/SSC Chelonian Specialist Group plans a high priority project on the ecology, reproduction and economic potential for the long-term management of Carettochelys. Because of lack of fundamental information, Carettochelys received a "K: Insufficiently Known" classification in the Red Data Book (Groombridge, 1982) and is not listed in the Appendices of CITES (1973). It has since received an Action Plan Rating of 1 (known threatened species in need of specific conservation measures) by the IUCN/SSC Freshwater Turtle Specialist Group (IUCN, 1989).

Groombridge (1982) reported that no conservation measures have been implemented in Papua New Guinea, though the declaration of certain wildlife management areas may protect it from non-native hunting pressures.

In Australia, Carettochelys benefits from State and Federal legislation prohibiting the exploitation of native fauna by all but Aboriginal peoples. It is protected throughout its documented range by the National Parks and Wildlife Conservation Act 1975 in Kakadu National Park and elsewhere in the Northern Territory by the Territory Parks and Wildlife Conservation Act 1982 (R. Jenkins, Pers. comm.). Export is prohibited under the Wildlife Protection (Regulation of Exports and Imports) Act 1982. However, such legislation does not protect the species from habitat destruction or modification. The provision of national parks and reserves would appear to be an appropriate response to ensure the conservation of a species that is locally abundant within a limited distribution. In Australia, Kakadu National Park affords the species considerable protection, and an intensive buffalo control programme is now in place. However, as outlined above, the park is currently a compromise between conservation, mining, recreation and other interests, and there are moves to annex important regions in the head-waters of the South Alligator drainage for mining by chemical extraction.

Conservation Measures Proposed

In view of the importance of Carettochelys as a food source for local people and the decentralized nature of the wildlife management authority in Papua New Guinea, any conservation measures need to be introduced with sensitivity (IUCN, 1989). There have been calls for the introduction of a scheme to protect nest sites against over-exploitation, perhaps allied to a closed season for hunting and egg collecting. However, firm data on trends in population numbers and levels of exploitation of Carettochelys for meat and eggs that could be used in support of these calls are lacking.

Preliminary research indicates the need for the following measures in Papua New Guinea, focusing especially on the Fly River catchment (IUCN, 1989):

• Comparative studies on the impact of different levels of exploitation of this species are needed to serve as a foundation for future monitoring of the turtle populations, and to enable future advice to be given to local communities to help them protect Carettochelys and its eggs.
• An assessment of the current intensity of exploitation is required to provide a basis for monitoring, and if necessary, controlling future trends in exploitation with changes in human populations and practices.
• An evaluation of the principal habitat requirements of Carettochelys is required in order to evaluate and respond to the potential impact of proposed, or potential, projects in river catchments, such as hydroelectricity schemes, mangrove clearing/woodchipping, etc.
• Population data are required to determine whether a management programme for ensuring a sustainable harvest of Carettochelys is necessary and attainable. Population data are required to determine whether a management programme for ensuring a sustainable harvest of Carettochelys is necessary and attainable.
• The population studies must be associated with research into the possibility of integrating a sustainable harvest system into local economies. This will almost certainly need to be backed up with a public awareness and education campaign. The programme will also include provision for training local wildlife staff and maintaining their operations.

Apart from the Alligator Rivers Region, the only other known concentration of pig-nosed turtles in northern Australia is in the Daly River. The Daly River is largely unprotected and control of even the river banks and important riparian vegetation is largely in private hands. The Northern Territory Government lacks a coherent river and wetland conservation strategy, but there are some promising initiatives on the horizon. A conservation and recreation development strategy for the wetlands between Darwin and the Arnhem Land escarpment is currently under consideration, though this strategy will not address problems faced in the Daly River catchment.

The land conservation section of the Conservation Commission of the Northern Territory is encouraging landholders in the Daly catchment to clear only in accordance with land capability, and the landholders are responding to this encouragement. They see the folly of clearing areas that are only peripherally suitable for agriculture or grazing. We may have seen the last of the wholesale clearing of land including drainage gullies and areas down to the water-line as has happened in the past in the Daly catchment. Another welcome initiative is the formation of land care groups encouraged by the Conservation Commission, such as the group recently formed in the Mary River region. These groups involve a broad spectrum of people interested in seeing both our heritage and our means of production preserved.

The Northern Territory Government should be encouraged to further develop these initiatives. Urgent consideration should be given to protecting the section of the Daly River corridor between Policeman's Crossing and the junction of the King River, and to protecting the riparian vegetation throughout the Daly drainage.

Captive Husbandry

Procedures for egg collection, transportation and artificial incubation have been established and can be incorporated into management programs with the option of accurately predicting and controlling hatchling sizes, sexes, amounts of internalized yolk and incubation times (Webb et al.,1986).

Carettochelys can be readily kept in aquaria in clean water maintained at a temperature between 28 and 30oC. A spacious tank with a diversity of underwater cover is required, as even small individuals can become aggressive and will habitually inflict damage to others of their species if confined together. In captivity, they will accept and thrive on a diverse diet of figs, apple, other fruits, eel weed (Vallisneria sp.), whitebait (Pisces) and shrimp.

Hatchling and sub-adult specimens are particularly susceptible to fungal white spot (Sphagnalium sp.) which if not treated promptly, kills young animals within a week (Mike Palmer-Allen, pers. comm.). It can be effectively treated externally by removing all loose skin and scabs and treating liberally with 1% Mercurichrome (Windholtz et al., 1983: 5698) or Acriflavine Solution (Windhotlz et al., 1983: 116), which is allowed to dry on the skin before the animals are returned to the tank.

Captive specimens are held in Australia at the Berry Springs Zoo (Darwin), Taronga Park Zoo (Sydney), Hartley Creek Crocodile Farm (Cairns), Beewah Animal Park (near Nambour) and the University of Canberra. Only the first two organizations are in a position to mount a captive breeding programme. Specimens at Berry Springs mated in 1989 after having been transferred from an outdoor enclosure earlier in the year, and the female subsequently laid eggs on the bottom of the aquarium. The aquarium now has an artificial nesting bank and the curator anticipates successful breeding in the near future (Lee Moyes, pers. comm.).

Current Research

Current research in Australia is supported by the Australian National Parks and Wildlife Service and the Conservation Commission of the Northern Territory. Studies of the effects of temperature on hatchling sex ratios in the field (Georges, submitted), nesting ecology (Georges, in prep), and population ecology (Heaphy, in prep) are nearing completion. A proposal for a study of the seasonal movements and wet season habitat requirements of Carettochelys in the Alligator Rivers region is being developed.

In Australia, it is important to know more of the distribution of Carettochelys, if only to better assess the value of the two known populations in the Daly River and the Alligator Rivers region. Work is also required to establish an ecological basis for the restricted distribution of Carettochelys which, according to data at hand, has very broad habitat requirements. Studies to date have not addressed seasonal movements and wet season requirements, nor do they address the requirements of juveniles, and the answers may lie there. Such information is needed before the possible impact of proposed or potential development within catchments (Groombridge, 1982; Georges & Kennett, 1988) can be assessed, and before the adequacy of existing reserves for protecting the species can be judged.

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Source

This article was prepared by Arthur Georges [Institute for Applied Ecology] and Mark Rose [The Wildlife Trust, 5 Fulbourne Manor, Fulbourn, Cambridge CB1 5BN, Cambridgeshire, United Kingdom] for Chelonian Conservation and Biology. You can subscribe to this journal by writing to Anders G.J. Rhodin (editor) , 168 Goodrich Street, Lunenburg, MA 01462, USA.