Consultation on Listing Status and Conservation Actions for the Pig-nosed Turtle

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Actions

Carettochelys insculpta (pig-nosed turtle) You are invited to provide your views and supporting reasons related to:

1) the eligibility of Carettochelys insculpta (pig-nosed turtle) for inclusion on the EPBC Act threatened species list in the Vulnerable category; and

2) the necessary conservation actions for the above species.

The purpose of this consultation document is to elicit additional information to better understand the status of the species and help inform on conservation actions and further planning. As such, the below draft assessment should be considered to be tentative as it may change following responses to this consultation process.

Evidence provided by experts, stakeholders and the general public are welcome. Responses can be provided by any interested person.

Anyone may nominate a native species, ecological community or threatening process for listing under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) or for a transfer of an item already on the list to a new listing category. The Threatened Species Scientific Committee (the Committee) undertakes the assessment of species to determine eligibility for inclusion in the list of threatened species and provides its

recommendation to the Australian Government Minister for the Environment.

Responses are to be provided in writing by email to:

[email protected]

Please include species scientific name in Subject field.

or by mail to:

The Director

Threatened Species Assessment Section

Department of Climate Change, Energy, the Environment and Water John Gorton Building, King Edward Terrace

GPO Box 3090 Canberra ACT 2601

Responses are required to be submitted by 4 August 2023.

Contents of this information package Page

General background information about listing threatened species 2

Information about this consultation process 3

Consultation questions specific to the assessment 4

Information about the species and its eligibility for listing 5

Conservation actions for the species 18

References cited 20

Listing assessment 25

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General background information about listing threatened species

The Australian Government helps protect species at risk of extinction by listing them as threatened under Part 13 of the EPBC Act. Once listed under the EPBC Act, the species becomes a Matter of National Environmental Significance (MNES) and must be protected from significant impacts through the assessment and approval provisions of the EPBC Act.

More information about threatened species is available on the department’s website at:

https://www.awe.gov.au/environment/biodiversity/threatened.

Public nominations to list threatened species under the EPBC Act are received annually by the department. In order to determine if a species is eligible for listing as threatened under the EPBC Act, the Threatened Species Scientific Committee (the Committee) undertakes a rigorous scientific assessment of its status to determine if the species is eligible for listing against a set of criteria. These criteria are available on the Department’s website at:

http://www.awe.gov.au/system/files/pages/d72dfd1a-f0d8-4699-8d43- 5d95bbb02428/files/tssc-guidelines-assessing-species-2021.pdf.

As part of the assessment process, the Committee consults with the public and stakeholders to obtain specific details about the species, as well as advice on what conservation actions might be appropriate. Information provided through the consultation process is considered by the Committee in its assessment. The Committee provides its advice on the assessment (together with comments received) to the Minister regarding the eligibility of the species for listing under a particular category and what conservation actions might be appropriate. The Minister decides to add, or not to add, the species to the list of threatened species under the EPBC Act. More detailed information about the listing process is at:

https://www.awe.gov.au/environment/biodiversity/threatened/nominations.

To promote the recovery of listed threatened species and ecological communities, conservation advices and where required, recovery plans are made or adopted in

accordance with Part 13 of the EPBC Act. Conservation advices provide guidance at the time of listing on known threats and priority recovery actions that can be undertaken at a local and regional level. Recovery plans describe key threats and identify specific recovery actions that can be undertaken to enable recovery activities to occur within a planned and logical national framework. Information about recovery plans is available on the department’s website at:

https://www.awe.gov.au/environment/biodiversity/threatened/recovery-plans.

Privacy notice

The Department will collect, use, store and disclose the personal information you provide in a manner consistent with the Department’s obligations under the Privacy Act 1988 (Cth) and the Department’s Privacy Policy.

Any personal information that you provide within, or in addition to, your comments in the threatened species assessment process may be used by the Department for the purposes of its functions relating to threatened species assessments, including contacting you if we have any questions about your comments in the future.

Further, the Commonwealth, State and Territory governments have agreed to share threatened species assessment documentation (including comments) to ensure that all States and Territories have access to the same documentation when making a decision on the status of a potentially threatened species. This is also known as the ‘Common

Assessment Method’ (CAM). As a result, any personal information that you have provided in connection with your comments may be shared between Commonwealth, State or Territory government entities to assist with their assessment processes.

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The Department’s Privacy Policy contains details about how respondents may access and make corrections to personal information that the Department holds about the respondent, how respondents may make a complaint about a breach of an Australian Privacy Principle, and how the Department will deal with that complaint. A copy of the Department’s Privacy Policy is available at: https://www.awe.gov.au/about/commitment/privacy .

Information about this consultation process

Responses to this consultation can be provided electronically or in hard copy to the contact addresses provided on Page 1. All responses received will be provided in full to the

Committee and then to the Australian Government Minister for the Environment.

In providing comments, please provide references to published data where possible. Should the Committee use the information you provide in formulating its advice, the information will be attributed to you and referenced as a ‘personal communication’ unless you provide

references or otherwise attribute this information (please specify if your organisation requires that this information is attributed to your organisation instead of yourself). The final advice by the Committee will be published on the department’s website following the listing decision by the Minister.

Information provided through consultation may be subject to freedom of information legislation and court processes. It is also important to note that under the EPBC Act, the deliberations and recommendations of the Committee are confidential until the Minister has made a final decision on the nomination, unless otherwise determined by the Minister.

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Consultation questions

PART 1 – INFORMATION TO AID LISTING ASSESSMENT

1. Do you have any additional information on the ecology or biology of the species?

2. Can you provide any additional information or estimates on longevity, average life span or generation length for the species?

3. Do you have additional information to support an estimate of the current population size of mature adults of the species (national extent)?

4. Do you have additional information on population trends over 3 generations, or an historic population size for the species (national extent)?

5. Do you have additional information on current range (national extent) or location of populations for the species?

6. Can you provide additional information on any change in range or location of populations, or an historic range (national extent)?

7. Are you aware of any cultural importanceor use that the species has?

PART 2 – INFORMATION FOR CONSERVATION ADVICE ON THREATS AND CONSERVATION ACTIONS

8. Do you have further information on the historic, current or potential threats facing the species?

9. Do you have further information on current or potential management actions to support protection and recovery of the species?

10. Do you have further information on current or potential monitoring or research activities for the species?

11. Are you aware of any other knowledge (e.g. traditional ecological knowledge) that may help better understand the threats and management actions to aid recovery of the species?

12. What individuals or organisations are currently, or potentially could be, involved in management and recovery of the species?

PART 3 – ANY OTHER INFORMATION

13. Do you have comments on any other matters relevant to the assessment of this species?

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DRAFT - Conservation Advice for Carettochelys insculpta (pig-nosed turtle)

In effect under the Environment Protection and Biodiversity Conservation Act 1999 from dd month yyyy.

This document combines the approved conservation advice and listing assessment for the species. It provides a foundation for conservation actions and further planning.

Carettochelys insculpta (pig-nosed turtle) © Copyright, Arthur Georges

This draft document is being released for consultation on the species listing eligibility and conservation actions

The purpose of this consultation document is to elicit additional information to better understand the eligibility of the species for listing and inform conservation actions, further planning and the potential need for a Recovery

Plan.

The draft assessment below should therefore be considered tentative at this stage, as it may change as a result of responses to this consultation process.

Note: Specific consultation questions relating to the below draft assessment and preliminary determination have been included in the consultation cover paper

for your consideration.

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Conservation status

Carettochelys insculpta (pig-nosed turtle) is proposed to be listed in the Vulnerable category of the threatened species list under the Environment Protection and Biodiversity Conservation Act 1999.

Carettochelys insculpta was assessed by the Threatened Species Scientific Committee to be eligible for listing as Vulnerable under criteria 2 and 3. The Committee’s assessment is at Attachment A. The Committee’s assessment of the species’ eligibility against each of the listing criteria is:

• Criterion 1: Insufficient data

• Criterion 2: B2ab(ii,iii,v): Vulnerable

• Criterion 3: C1: Vulnerable

• Criterion 4: Ineligible

• Criterion 5: Insufficient data

The main factors that make the species proposed for listing in the Vulnerable category are its restricted Area of Occupancy, continuing decline in habitat quality owing to altered flood regimes caused by climate change, damage to nesting areas by Bubalus bubalis (Asian water buffalo) and Bos taurus (cattle), and the possible future threats of disease and water extraction.

Species can also be listed as threatened under state and territory legislation. For information on the current listing status of this species under relevant state or territory legislation, see the Species Profile and Threats Database.

Species information

Taxonomy

Conventionally accepted as Carettochelys insculpta Ramsay 1886, Family: Carettochelyidae. Carettochelys insculpta is the last remnant species within the family Carettochelyidae, a once diverse lineage of turtles widespread throughout the northern hemisphere. Restricted to northern Australia and southern New Guinea, there is considerable genetic structuring of populations (Young 2022, pers comm, 1^st February 2022), but no subspecies are currently recognised.

Description

The pig-nosed turtle is a very large freshwater turtle, within Australia it weighs up to 16 kg.

Straight carapace lengths (CL) of up to 45.4 cm for males and 52.3 cm for females have been recorded at the Pul Pul billabong within the South Alligator River catchment, Northern Territory (Georges & Kennett 1989). In New Guinea, the species is generally larger (up to 22 kg in weight and 57 cm in CL; Kikori River PNG – Doody et al. 2008). The carapace of adults is rounded anteriorly and flattens laterally. The shell is covered with continuous skin without epidermal scutes, a characteristic also found in softshell turtles (family Trionychidae), from which the pig- nosed turtle can be distinguished by the retention of peripheral bones in the carapace, giving it a rigid margin. The carapace of adults is grey to olive in colour. The skin on the dorsal surface of

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the head, neck and limbs is also grey, while the ventral surface, including the jaw, is creamy- white to white in colour. The neck and head retract into the shell vertically (cryptodirous) as opposed to laterally (pleurodirous). The nostrils are positioned at the end of a fleshy proboscis and point forward and downward, forming a “pig-like” snout. The lateral and anterior sides of the nostrils are covered in tubercules. The pig-nosed turtle has flipper-like forelimbs which are elongated and compressed, with claws on the first two digits. Males have a longer tail than females but otherwise the sexes are indistinguishable.

Hatchlings have well-formed limbs on emergence and the plastron and carapace are extremely soft, stiffening in the few hours after hatching. The carapace of hatchlings is pale grey in colour, with serrated white margins. Average weight of hatchlings from the Daly River is 19 g. Average carapace length of hatchlings is 4.1 cm and average carapace width is 3.8 cm (Webb et al. 1986).

Distribution

The pig-nosed turtle is found in northern Australia and southern rivers of the island of New Guinea (Georges & Wombey 1993). In Australia, the species occurs in the larger rivers of the Northern Territory. This includes the Daly River and the Katherine and Flora tributaries (Cann 1972; Webb et al. 1986; Doody et al. 2000; Rea et al. 2002; Washusen 2022, pers comm, 26 April 2022; Griffiths 2022, pers comm, 23 November 2022) and the East and South Alligator Rivers (Schodde et al. 1972; Georges & Kennett 1988). The species has also been documented in the Victoria drainage (Cogger 1994); however, the Traditional Custodians of the Victoria River catchment area are not aware of the pig-nosed turtle occurring within the catchment and field searches between July and September 2018 did not locate the species, suggesting there is no resident population (Young 2022, pers comm, 1^st February 2022). There have been anecdotal reports of the pig-nosed turtle from the Adelaide, Darwin, McKinlay and Roper Rivers of the Northern Territory (Cann 1972); however, the validity of these reports has not been

substantiated (Georges et al. 2008) with the exception of a single specimen captured at Roper Bar (Georges 2022, pers comm, 17 May 2022). Traditional Custodians have reported the presence of the pig-nosed turtle in the Fitzmaurice River of the Northern Territory (Georges et al. 2008), but no intensive surveys of the river have occurred.

The species is considered locally abundant in some areas within Australia, and subpopulations within Australia and New Guinea show considerable genetic structure, suggesting long standing isolation (Young 2022, pers comm, 1^st February 2022). The Australian subpopulations have low genetic diversity compared with those of New Guinea, and the Daly River subpopulation in particular has exceptionally low genetic diversity (Young 2022, pers comm, 1^st February 2022).

This suggests that the subpopulation has historically experienced a major genetic bottleneck and is potentially experiencing a bottleneck at present, given its low population densities.

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Map 1 Modelled distribution of the pig-nosed turtle

Source: Base map Geoscience Australia; species distribution data Species of National Environmental Significance database.

Caveat: The information presented in this map has been provided by a range of groups and agencies. While every effort has been made to ensure accuracy and completeness, no guarantee is given, nor responsibility taken by the Commonwealth for errors or omissions, and the Commonwealth does not accept responsibility in respect of any information or advice given in relation to, or as a consequence of, anything containing herein.

Species distribution mapping: The species distribution mapping categories are indicative only and aim to capture (a) the habitat or geographic feature that represents to recent observed locations of the species (known to occur) or habitat occurring in close proximity to these locations (likely to occur); and (b) the broad environmental envelope or geographic region that encompasses all areas that could provide habitat for the species (may occur). These presence categories are created using an extensive database of species observations records, national and regional-scale environmental data, environmental modelling techniques and documented scientific research.

Cultural and community significance

The cultural, customary and spiritual significance of species and the ecological communities they form are diverse and varied for Indigenous Australians and their stewardship of Country. This section describes some examples of this significance but is not intended to be comprehensive or applicable to, or speak for, Indigenous Australians. Such knowledge may be held by Indigenous Australians who are the custodians of this knowledge and have the rights to decide how this knowledge is shared and used.

The origins of Warradjan (the pig-nosed turtle) are described in Indigenous tribal legend (Georges & Kennett 1988). The pig-nosed turtle is represented in Indigenous rock art of the Alligator Rivers region and Arnhem Land, suggesting the species is a long-term resident of northern Australia (Georges & Kennett 1989).

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Turtles are regularly eaten by Indigenous Australians in northern Australia, with the pig-nosed turtle favoured due to their taste and size (Press 1986). Traditionally, the pig-nosed turtle was hunted by Indigenous men from the Alligator River region by spearing the turtles from trees that lined the banks of billabongs, by diving on the turtles from the bank or by waiting quietly in the water as other men herded the turtles towards them (Georges & Kennett 1988). Today, the pig- nosed turtle is caught on baited hand lines and then roasted whole in a pit (Georges & Kennett 1988). Hot stones are placed inside the turtle’s body cavity and the turtle is covered in coals, hot rocks, paperbark and soil (Georges & Kennett 1988). Indigenous communities eat pig-nosed turtles, both routinely and for ceremonial purposes, whereby the turtles may be transported substantial distances (and out of range). However, there is no evidence that the Indigenous harvest is particularly taking advantage of vulnerabilities of the species (e.g., predictable nesting locations) or that modern technologies are being employed to inflate the levels of harvest above traditional levels. For this reason, Indigenous harvest is not considered a contemporary threat to the persistence of the species. There are no reports of Indigenous Australians harvesting the eggs of the pig-nosed turtle (Georges & Rose 1993).

The pig-nosed turtle is the symbol for the Wagiman Rangers groups and is highly regarded in the Wagiman region (Freshwater Turtles on Country Workshop Darwin 2022). The species also occurs on Wardaman and Njanjma land. Wardaman and Wagiman Rangers have expressed interest in developing future monitoring and research projects, particularly in areas where water extraction for cotton and other agriculture is affecting waterways (Freshwater Turtles on Country Workshop Darwin 2022). Wagiman Rangers have observed the Daly River water level dropping in recent years and have concerns that this may be affecting the turtles and the overall landscape (Freshwater Turtles on Country Workshop Darwin 2022).

This statement of significance is not intended to be comprehensive, applicable to, or speak for, all Indigenous Australians. It is acknowledged that Indigenous Australians who are the custodians of this knowledge have the rights to decide how it is shared and used.

Relevant biology and ecology

Habitat

The habitat requirements of the pig-nosed turtle are diverse, with the species occupying

permanent lentic (still freshwater) and lotic (moving freshwater) habitats (Doody et al. 2000) of the Daly River, the East Alligator River and the South Alligator River (Young 2022, pers comm, 1^st February 2022). The Daly River is a spring-fed system, characterised by clear, shallow water in the dry season (May to October) and turbid, deep water in the wet season (Doody et al.

2003a). The pig-nosed turtle occupies the middle reaches of the Daly River, between the escarpment and the saline sections (Doody et al. 2003a). Females in the Daly River have been observed at an average depth of 1.5 ± 0.7 m (range 0.2 – 4 m) while males have been observed at shallower depths, at an average of 0.9 ± 0.5 m (range 0.2 – 3 m; Doody et al. 2002). Microhabitats occupied by males and females differ (Doody et al. 2002). Males tend to utilise isolated logs at shallower depths more than females, while females frequently use deeper, open sand flats (Doody et al. 2002).

In the Alligator River region, the species occurs in billabongs and plunge pools (deeper water at the foot of a waterfall) (Georges & Kennett 1989), with an average depth of 2 m (Georges & Rose 1993). The pig-nosed turtle prefers sand and gravel substratum with a layer of leaf litter and silt (Georges & Wombey 1993). Fallen trees and branches on the banks of billabongs provide leaf

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litter which the species may use for cover. Dense broad-leaf forest line the banks of billabongs in the Alligator River region. Georges & Kennett (1989) suggest the species may aggregate in the upper reaches of the South Alligator River in the dry season (e.g., Barramundi Creek and the headwaters of the South Alligator River above Pine Creek road crossing).

Little is known of the habitat used by hatchlings and very small juveniles. One observation is of a hatchling in the Daly River buried in the root mass of submerged Pandanus roots and stems 1 km upstream of Policeman's Crossing. It is assumed that they suffer high mortality in these early years from a range of predators, and that those that survive have highly cryptic habits (Georges 2022, pers comm, 17 May 2022).

The pig-nosed turtle is not known to occur in estuarine areas of Australia (Georges & Kennett 1989).

Life-history and reproduction

The pig-nosed turtle is long-lived, has high mortality early in life and a delayed onset of sexual maturity (Iverson 1991). Age at sexual maturity is estimated at 20 to 22 years for females and 14 to 16 years for males (Heaphy 1990). The estimated life expectancy is 80 years, based on von Bertalanffy growth curves which show an estimated endpoint of reproductive activity at 80 years of age (Heaphy 1990). The generation length of the species is not known with certainty.

The pig-nosed turtle lays eggs into nests in the late-dry season in Australia (Georges & Rose 1993). At Daly River, the nesting season occurs between mid-August and early October (Georges

& Kennett 1989). In the Alligator Rivers, nesting occurs from mid-July to early November (Georges & Kennett 1989). The pig-nosed turtle nests in fine riverbank sand or on isolated sand bars, in areas with minimal vegetation (Webb et al. 1986; Georges & Kennett 1989; Doody et al.

2003b). Pig-nosed turtle nests have also been recorded in gravel and loamy sand (Doody et al.

2003b).

Pig-nosed turtles predominantly nest at night. In the Daly River, nests were on average 4 m from the water’s edge and 1.6 m above the water level (Georges 1992). Pig-nosed turtles appear to select nesting beaches with sand moisture content averaging 6% (Doody et al. 2003b). The low nest height may increase the susceptibility of nests to flooding, if early onset of wet season rain occurs (Webb et al 1986). Nests are shallow, with nests located on the Daly River having a mean depth of 13 ± 3 cm (Webb et al. 1986) and are very susceptible to trampling by cattle and buffalo.

The pig-nosed turtle follows a biennial breeding cycle, whereby females produce eggs every second year, and produce two clutches within breeding years (Georges & Rose 1993; Doody et al. 2003a). In the Daly River, 80% of gravid females nested twice in a year, while 20% nested once (Doody et al. 2003a). Average clutch size in the Daly River was 10.5 ± 0.4 eggs (range 7 to 15 eggs; Georges 1992). Mean egg mass in the Daly River is 34 ± 4 g (Webb et al. 1986).

Incubation time is variable and dependent on incubation temperature, as for all ectotherms. At 28°C incubation duration is 101 days, at 30°C incubation duration is 69 days and at 32°C

incubation duration is 53 days (Webb et al. 1986). Hatching of pig-nosed turtles is stimulated by early season rain or flooding. The emergence of hatchlings at the onset of the wet season, after prolonged periods of dry condition, likely allows the species to disperse under more favourable conditions (Webb et al. 1986; Doody et al. 2001).

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The pig-nosed turtle exhibits embryonic aestivation, whereby well-developed hatchlings remain in the egg and delay hatching, usually until environmental conditions are favourable (Webb et al.

1986; Doody et al. 2001). During embryonic aestivation the metabolic rate of pig-nosed turtle hatchlings is reduced and embryonic growth ceases (Georges & Rose 1993). Pig-nosed turtles hatch at the onset of the wet season, after prolonged periods of dry conditions (Webb et al.

1986). Embryonic aestivation is likely an adaptation that synchronises hatching with the onset of the wet season when environmental conditions are more favourable (Georges 1992).

The pig-nosed turtle is the only Australian freshwater turtle species known to exhibit temperature-dependent sex determination (Type 1A) (Webb et al. 1986), whereby the temperature experienced during the embryonic stage influences the offspring sex. A

temperature of 32 °C produces both males (~60%) and females (~40%), with males coming from the deeper, cooler eggs (Georges 1992; Young et al. 2004). An incubation temperature of 31.5 °C or below, produces 100% males, while an incubation of 32.5 °C or above produces 100%

females (Young et al. 2004). No eggs survive incubation temperatures above 36 °C (Young et al.

2004).

Diet

The pig-nosed turtle is omnivorous (Georges & Wombey 1993). Turtles feed predominantly on seeds, leaves and fruits of riparian vegetation such as Ficus racemosa (cluster fig), Syzgium forte (white bush apple), Pandanus aquaticus (screwpines) and Sonneratia species (mangroves) during the dry season (Georges & Wombey 1993). The pig-nosed turtle also consumes aquatic vegetation such as ribbonweed, algae and Najas tenuifolia (water nymph). Animal matter consumed includes molluscs, crustaceans, fishes and carrion (Georges & Wombey 1993; Welsh et al. 2017). The hair, flesh and bones of Pteropus sp. (flying fox) were found in the stomach contents of a male from Jim Jim Creek (Georges & Kennett 1989, see also Georges et al. 1989) and benthic macroinvertebrates were also found in the stomachs of some pig-nosed turtles of Pul Pul billabong (Georges & Kennett 1989).

Movement

Pig-nosed turtle subpopulations comprise individuals with high site fidelity as well as transient individuals which appear to move considerable distances (Doody et al. 2000). Radio tracking in the Daly River during the dry season (August to November) of 1996 and the wet season of 1996 to 1997 found females moved on average a distance of 633 ± 399 m, while males moved on average 272 ± 79 m (Doody et al. 2002). The linear home range of radio-tracked non-gravid females was 7.8 ± 0.8 km and was greater than the linear home range length of males at 3.2 ± 1.3 km (Doody et al. 2002). Females were also more active than males during the day. Activity levels of males increased when females were gravid (Doody et al. 2002). Gravid females had a linear home range of 8.6 ± 3.7 km and moved on average a distance of 756 ± 465 m between sightings.

During nesting, gravid females move up to 5 km in search of suitable nesting beaches (Doody et al. 2009). During the wet season, pig-nosed turtles move out of the river channel during flooding and occupy billabongs or river swamp environments (Doody et al. 2002).

The pig-nosed turtle vocalises underwater, emitting sounds which are consistent with contact calls (Ferrara et al. 2017).

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Habitat critical to the survival

The habitat critical to the survival of the pig-nosed turtle is the rivers and streams of the Daly River and the Katherine and Flora tributaries with these characteristics:

• Continuous low flow, with connectivity between sites to allow turtles to move along and between catchments.

• Access to spring fed systems or reaches with well-developed riparian vegetation and instream structure.

• Fine sand on the riverbank or on isolated sand bars, in areas with minimal vegetation within 4 m from the water’s edge for nesting.

Furthermore, the upper reaches of the South Alligator River such as Pul Pul billabong and the billabongs of Barramundi Creek are important refuges utilised by the pig-nosed turtle during the dry season, given the high abundance of the species found there (Georges & Kennett 1989).

Any breeding or foraging habitat in areas where the species is known or likely to occur and any newly discovered breeding or foraging sites should be considered habitat critical to the survival, as should areas required to facilitate movement between foraging or breeding areas. Areas that are not currently occupied by the species, but which may become suitable in the future, should also be considered habitat critical to survival.

No Critical Habitat as defined under section 207A of the EPBC Act has been identified or included in the Register of Critical Habitat.

Important populations

In this section, the word population is used to refer to subpopulation, in keeping with the terminology used in the EPBC Act and state/territory environmental legislation.

The pig-nosed turtle is the last remaining member of the Family Carettochelyidae, which was once widespread in the late Tertiary (Pritchard 1979). Given the pig-nosed turtle’s eligibility for listing as Vulnerable, all populations should be considered as important populations and under pressure to persist. Therefore, all populations require protection to support the overall recovery of the species.

Threats

The low genetic diversity of the Australian pig-nosed turtle subpopulations makes the species highly susceptible to threats. The pig-nosed turtle is threatened by novel diseases, water extraction for agricultural practices, Asian water buffalo and feral and managed cattle, changes in flood regimes and increasing temperatures. Further, predation by native species such as Varanus panoptes (yellow-spotted monitors) and Varanus mertensi (Merten’s water monitors) have been included as threats as their impact is exacerbated by the low population sizes of the Australian pig-nosed turtle.

Table 1 Threats

Threats in Table 1 are noted in approximate order of highest to lowest impact, based on available evidence.

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Threat Status ^a Evidence Disease

Susceptibility to novel diseases

• Timing: future

• Confidence: inferred

• Likelihood: possible

• Consequence: catastrophic

• Trend: unknown

• Extent: unknown

The exceptionally low genetic diversity of the pig- nosed turtle population makes the species highly susceptible to declines caused by disease (Young 2022, pers comm, 2^nd February 2022). In an analogous case in 2015, a novel nidovirus caused mortality of Myuchelys georgesi (Bellinger River saw-shelled turtle), a species with similarly low genetic diversity (Georges & Spencer 2015). The impact of the virus on that species was catastrophic (Chessman et al. 2020) with 90% of the population being wiped out.

If a disease like the Bellinger River virus (BRV) were to impact the pig-nosed turtle, it is likely the population would experience a similar severe decline given the species’ low genetic diversity.

Habitat modification and destruction Dry season water

extraction for agricultural practices

• Timing: future

• Confidence: projected

• Consequence: major

• Trend: unknown

• Extent: across part of its range

The rivers of the Northern Territory discharge 70%

of Australia’s available freshwater and consequently there is pressure to divert water from these rivers for use in the agricultural sector for irrigation (Georges et al. 2008).

The Daly River catchment has been considered a focus for agricultural development, with the possibility of extracting water from dry season flows via surface and ground water offtake. The Oolloo aquifer on the Daly is currently subject to a water allocation planning process with

consideration towards the pig-nosed turtle (Northern Territory Government 2019).

Georges et al. (2002) modelled the impact of flow reduction on habitat viability along 74 km of the Daly River. Under the most conservative scenario (3 cumecs), a cease-to-flow year (which does not occur under natural conditions) would occur

approximately every 9 years.

A reduction in flow would fragment the distribution of the pig-nosed turtle into disconnected pools, restricting male and female movement and limiting access to critical resources, including nesting beaches, ribbonweed and river-bed springs. These conditions would seriously deplete the local population due to reproductive failure and resource limitation (Georges et al. 2002).

Invasive species

Asian water buffalo • Timing: historical

• Confidence: observed

• Likelihood: almost certain

• Consequence: moderate

• Trend: static

• Extent: across the entire range

Asian water buffalo are distributed across the Top End of Australia, with 150,000 individuals estimated in 2008 (Commonwealth of Australia 2011). In the Alligator River region of northern Australia, Asian water buffaloes pose a threat to the pig-nosed turtle and its habitat by trampling nesting habitat and destroying turtle nests in the process (Georges &

Kennett 1989; Georges & Rose 1993). In 1987, densities of Asian water buffaloes were so high that all potential nesting habitat was trampled (Georges

& Kennett 1989). Given the shallow nest depth of pig-nosed turtles, trampling is likely to be of significant impact to recruitment.

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Threat Status ^a Evidence

Asian water buffalo also destroy the riparian vegetation relied upon by the pig-nosed turtle by foraging and structurally destroy the banks of billabongs (Georges & Rose 1993).

Georges et al. (2008) suggest that Asian water buffalo numbers have been drastically reduced in Kakadu National Park and other areas of the Northern Territory, likely benefitting the pig-nosed turtle. However, recent data on the impact of Asian water buffalo on pig-nosed turtles across the species range is lacking and it is unknown whether nests of the pig-nosed turtle are still affected by Asian water buffalo.

Predation by Sus scrofa (feral pigs)

• Timing: current, future

• Confidence: suspected

• Likelihood: likely

• Trend: unknown

• Extent: across part of the range

Although there is no direct evidence to suggest that feral pigs are depredating pig-nosed turtle nests, they predate heavily on both eggs and adults of other turtle species in northern Australia (e.g., Chelodina rugosa, Fordham et al. 2006) with impacts an order of magnitude greater than Indigenous harvest. Given the low effective population size of pig-nosed turtles across the three subpopulations (Young 2022, pers comm, 2^nd February 2022), any threat which has the potential to reduce hatchling survival is likely to be detrimental to the species.

Invasive weeds • Timing: historical, current

• Confidence: suspected

• Trend: unknown

• Extent: across part of the range

Given the pig-nosed turtle has temperature- dependent sex determination (Webb et al. 1986), shading of the riverbank by invasive weeds may alter pig-nosed turtle sex ratios, if suitable nesting sites are not available elsewhere. Invasive flora species such as Jatropha gossypiifolia (bellyache bush) is an increasing threat in the Gwinning River and Daly River. Bellyache bush has the potential to dominate riparian vegetation and shade the riverbank relied upon by pig-nosed turtles during nesting (Washusen 2022, pers comm, 26 April 2022) although the impacts of weeds are not well understood.

Climate change

Change in flood regimes • Timing: current/future

• Trend: increasing

Flooding is the main cause of embryonic mortality in pig nosed turtles, particularly in seasons after a below average wet season. When turtles nested late on the Daly River after a below average wet season, nest mortality owing to flooding was 20% (Doody et al. 2004). Most nests destroyed by floods were laid at low elevations and had not completed

development by the time flooding began (Doody et al. 2004). It is unknown whether subpopulations in the South and East Alligator River systems also experience nest mortality from flooding; however, given all subpopulations experience the wet-dry seasons of the Northern Territory it is likely the South and East Alligator River systems are similarly affected.

Extreme changes to wet/dry cycles and flooding regimes as a result of climate change would likely influence both sex ratio, and juvenile survival rates (Georges et al. 2002). In particular, if cease to flow conditions come to apply to the Daly River as a consequence of altered wet/dry cycles and more intensive water resource development, substantial

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changes to the demography and persistence of the turtles would likely result (Georges et al. 2002).

Increase in ambient

temperatures • Timing: future

• Trend: increasing

The Top End of Australia is predicted to experience a 0.5 – 1.4°C increase in the average temperature by 2030. By 2050, warming is expected to range from 0.7 – 1.6°C (under a low emissions pathway) to 1.4 – 2.4 °C (under high emissions) (NESP Earth Systems and Climate Change Hub 2020). By the middle of the century, the number of days per year over 35 °C will double in some locations across the Northern Territory (NESP Earth Systems and Climate Change Hub 2020). A rise in ambient temperature will result in a rise in nest temperatures,

notwithstanding that solar irradiation is the predominant driver of nest temperatures (George 1992). Given the species has temperature- dependent sex determination, increasing

temperatures may alter hatchling sex-ratios, with a greater bias towards females (Georges 1992; Young et al. 2004). Additionally, changes in ambient temperatures are likely to affect water temperature and the cues pig-nosed turtles use to nest. Georges et al. (2002) predict that a 1°C change in

temperature could be expected to result in a ~ 7- day shift in the timing of nesting.

Habitat modification and destruction

Mining activity • Timing: future

• Trend: decreasing

Exploration and mining by chemical extraction was planned for the headwaters of the South Alligator River (Georges et al. 2008). While mining is no longer considered a current pressure on the populations of pig-nosed turtles (Georges et al.

2008), it has the potential to cause pollution of waterways through contaminated rainwater run-off and accidental spillage of hazardous chemicals. The demand for water for mining activities may reduce water levels in billabongs relied upon by the pig- nosed turtle in the dry season (Georges et al. 2008).

Agricultural practices • Timing: current and future

• Trend: unknown

• Extent: unknown

Agricultural activities in the Daly River drainage may impact the pig-nosed turtle through clearance of riparian vegetation and increased erosion and siltation of waterways (Georges & Rose 1993;

Georges et al. 2008).

Cattle grazing and trampling

• Timing: historical/current

• Trend: unknown

Trampling by livestock such as cattle has been a known source of turtle mortality in the Daly River region since the 1980s (Georges & Kennett 1989).

This grazing also degrades sections of the river, resulting in erosion, reduced riparian vegetation and increased influxes of sediment. Recent data on the impact of cattle on pig-nosed turtles across the species’ range is lacking and it is unknown whether nests of the pig-nosed turtle are still affected by cattle.

Native species

Predation by the yellow- spotted monitor and Merten’s water monitor.

• Timing: historical

Predation by native species is included in the context of its potential to compound the impact of other threats. Pig-nosed turtle nests are predated by the yellow-spotted monitor and Merten’s water

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• Trend: unknown

monitor in the Daly River. Between 1996 and 1998, predation rates by the yellow-spotted monitor ranged from 17 to 23% (Doody et al. 2006). In 1996, 1997 and 1998, 66 nests, 86 nests and 138 nests were depredated respectively (Doody et al. 2006).

Predation occurred the day after the eggs were laid.

In 1996, 80% of destroyed nests were taken within the first 24 hours (Doody et al. 2004). Doody et al.

(2006) suggest that the population of yellow- spotted monitors experienced a decline with the arrival of Bufo marinus (cane toads) in 2003–04 to the point where the yellow-spotted monitor was no longer considered a significant predator of pig- nosed turtle nests. It is unknown if the population of yellow-spotted monitors has since increased and whether nest predation rates have increased.

Given the low effective population size of pig-nosed turtles across the three subpopulations (Young 2022, pers comm, 2^nd February 2022), any threat which has the potential to reduce hatchling survival is likely to be detrimental to the species.

Predation of pig-nosed turtles by Crocodylus sp.

(crocodiles)

• Timing: current, future

• Consequence: minor

• Trend: unknown

• Extent: unknown

Predation by crocodiles has been included in the context of its potential to compound the impact of other threats. Crocodiles are known to predate on pig-nosed turtles in New Guinea. During field surveys between 2016 and 2018 an adult female pig-nosed turtle was observed being predated upon by a large crocodile. The pig-nosed turtle appeared to be taken by the crocodile as it emerged from the water to nest (Young 2022, pers comm, 1^st February 2022). A large crocodile which was killed by Indigenous New Guinea people was also found to have the limbs of a pig-nosed turtle in its stomach (Young 2022, pers comm, 1^st February 2022). An increase in the number of crocodiles may have a detrimental impact on the pig-nosed turtle population in Australia; however, information on current predation rates is lacking.

aTiming—identifies the temporal nature of the threat

Confidence—identifies the nature of the evidence about the impact of the threat on the species

Likelihood—identifies the likelihood of the threat impacting on the whole population or extent of the species Consequence—identifies the severity of the threat

Trend—identifies the extent to which it will continue to operate on the species Extent—identifies its spatial context in terms of the range of the species Categories for likelihood are defined as follows:

Almost certain – expected to occur every year

Likely – expected to occur at least once every five years Possible – might occur at some time

Unlikely –known to have occurred only a few times

Unknown – currently unknown how often the threat will occur Categories for consequences are defined as follows:

Not significant – no long-term effect on individuals or populations Minor – individuals are adversely affected but no effect at population level Moderate – population recovery stable or declining

Major – population decline is ongoing

Catastrophic – population trajectory close to extinction

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Each threat has been described in Table 1 in terms of the extent that it is operating on the species. The risk matrix (Table 2) provides a visual depiction of the level of risk being imposed by a threat and supports the prioritisation of subsequent management and conservation actions.

In preparing a risk matrix, several factors have been taken into consideration, they are: the life stage they affect; the duration of the impact; the spatial extent, and the efficacy of current

management regimes, assuming that management will continue to be applied appropriately. The risk matrix and ranking of threats has been developed in consultation with experts and using available literature.

Table 2 Risk Matrix

Likelihood Consequences

Not significant Minor Moderate Major Catastrophic

Almost certain Asian water buffalo

Likely Change in flood

regimes Increase in ambient temperatures

Predation by feral pigs

Possible Predation of

adult pig- nosed turtles by crocodiles

Mining activity

Agricultural practices Predation by yellow-spotted monitor and Merten’s water monitor

Invasive weeds

Cattle grazing and trampling

Dry season water extraction for agricultural practices

Susceptibility to novel diseases

Unlikely Unknown

Risk Matrix legend/Risk rating:

Low Risk Moderate Risk High Risk Very High Risk

Priority actions have then been developed to manage the threats, particularly where the risk was deemed to be ‘very high’ (red shading) or ‘high’ (orange shading). For those threats with an

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unknown or low risk (blue and green shading respectively) research and monitoring actions have been developed to understand and evaluate the impact of the threats, where appropriate.

Conservation and recovery actions

Primary conservation objective

The pig-nosed turtle population is sustained and protected in the Northern Territory, with all age classes represented throughout the species’ range in Australia. The area of occupancy and extent of occurrence of the pig-nosed turtle is maintained or increased.

Conservation and management priorities

Habitat loss, disturbance and modifications impacts

• Improve the coverage of protected areas across the species’ range, with particular focus on areas where all age classes of pig-nosed turtles are represented.

• Ensure water allocations do not result in barriers to the movement of pig-nosed turtles.

• Monitor water extraction during drought and for agriculture to ensure the availability of sufficient water for the turtles. Liaise with water management authorities to create triggers around cease-to-flow actions in the event of drought.

• Reduce the impact of buffalo and cattle around rivers and billabongs through maintenance of sustainable stocking rates and monitoring of populations. Where applicable, implement fencing around priority nesting sites to reduce buffalo access to waterbodies.

• Manage weed infestations around pig-nosed turtle nesting sites to increase the suitability of nesting locations.

Disease

• Monitor the species for the presence of disease and implement suitable hygiene protocols, including washing and sterilisation of aquatic equipment used in the catchment. Issue a public recommendation for the management of hygiene, washing and sterilisation of aquatic equipment used in the catchments generally.

Increased intensity and frequency of floods

• Conduct targeted monitoring of the species to detect egg mortality due to inundation from flood events. Monitoring of hatching success at priority nesting sites should occur every 5 years, with priority given to years with increased flood risk.

• Conduct broadscale monitoring of the species to detect impacts of flooding on the turtles and their habitat, in particular increased short-term nutrification and long-term

sedimentation/substrata effects.

Impacts of native species

• Monitor native yellow-spotted monitor and Merten’s water monitor predation rates and prioritise the protection of nests if predation rates are known to be, or suspected to be, limiting the recruitment of the pig-nosed turtle.

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Ex situ recovery actions

• Consider inducing egg laying in wild gravid females (using hormones) to provide eggs for artificial incubation, if hatchling recruitment is determined to be limited.

• Consider developing an ex-situ head-starting program (raising of wild-origin juveniles under ex situ conditions and returning those individuals to the wild subpopulation at a later stage) for the pig-nosed turtle, if survival of hatchling and juvenile turtles is limited.

• Investigate translocating pig-nosed turtles between subpopulations. When doing so consider treating the subpopulations as distinct genetic units, but also explore the possibility of assisted gene flow between subpopulations as a priority action to increase genetic variation in Australian populations.

Stakeholder engagement/community engagement

• Encourage stakeholders to report any sightings of pig-nosed turtles via the TurtleSAT citizen science program (http://www.turtlesat.org.au), the NT Natural Resources Maps (NR Maps; https://nrmaps.nt.gov.au/nrmaps.html) and iNaturalist

(https://www.inaturalist.org/)

• Educate communities in the local catchment to identify predated nests and protect intact nests as instructed in the 1 Million turtles program (https://1millionturtles.com/). This work needs to be done in close collaboration with relevant local community groups.

• Actively engage Traditional Custodians in the conservation of the species and its habitat and work with them to preserve their traditional knowledge on turtles and associated values.

• Engage with Traditional Custodians to determine how they can be involved in the species’

conservation and how the work can be mutually beneficial. Offer support and training for Indigenous-led on-ground management actions.

Survey and monitoring priorities

• Monitor population change throughout the species’ range (Daly, South Alligator and East Alligator Rivers) by ongoing surveying of sites, with a focus on population size and

demographics. Priority areas for monitoring should be chosen in the context of current and future threats.

• Collate data from netting and trapping surveys on the Adelaide, Darwin, McKinlay, Roper and Fitzmaurice Rivers of the Northern Territory and Arnhem Land for pig-nosed turtles, to determine the validity or otherwise of anecdotal reports.

• Determine the size of the pig-nosed turtle population. Population size can be estimated with multiple sample points at representative locations and extrapolated out to cover the whole catchment. Distinction needs to be made between an index of abundance (useful for

monitoring trends) and estimates of actual abundance (useful for assessing extinction risk).

Sampling should be repeated at 5-year intervals with appropriate precision to enable assessment of trends.

• Continue to monitor the genetic diversity of the pig-nosed turtle population. Genetic diversity should be assessed using modern approaches (e.g., Single Nucleotide

Polymorphisms) and an appropriate index (e.g., heterozygosity, or percentage shared alleles among individuals) again with appropriate errors to enable a robust assessment of trends

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in time and across locations (differing in population size). This should involve periodic surveys and sampling of newly recruited cohorts (e.g., every 5 years).

• Monitor proposed mining activities, including the issuing of extractive mining licenses, and implement measures to ensure the impacts of mining on the pig-nosed turtle are

understood and mitigated.

Information and research priorities

• Determine the ecology and movement patterns of hatchling and juvenile (i.e., 1 to 5 years old) pig-nosed turtles through radio telemetry and mark-recapture. A particular focus should be given to their habitat use and survival rates.

• Determine the extent of predation on pig-nosed turtle nests by yellow-spotted monitors and Merten’s water monitors in different catchments, and the factors that contribute any

variation in this nest predation. This research should be conducted in collaboration with any existing research projects on either monitor species.

• Determine the extent of crocodile predation on adult pig-nosed turtles, through communication with Traditional Custodians and collation of anecdotal reports and monitoring of nesting beaches during the nesting season using camera traps. Monitor the population size of crocodiles to determine if an increase in numbers leads to greater pig- nosed turtle predation.

• Understand environmental water flow requirements of the pig-nosed turtle.

• Determine Indigenous harvest rates of pig-nosed turtles in the Daly, East Alligator and South Alligator River systems, and assess sustainability given population trends and breeding success.

• Determine the impact of increasing atmospheric temperatures with climate change, on nest incubation temperatures (i.e., soil temperatures) and hatchling sex ratios.

Links to relevant implementation documents

This Conservation Advice is developed to be able to subsequently inform other planning instruments such as a Bioregional Plan or a multi-entity Conservation Plan.

Threat abatement plan for predation, habitat degradation, competition and disease transmission by feral pigs (2017)

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