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Consultation Document on Listing Eligibility and Conservation Actions

Varanus mertensi (Mertens’ Water Monitor)

Image: Simon Ward

You are invited to provide your views and supporting reasons related to:

1) the eligibility of Varanus mertensi (Mertens’ Water Monitor) for inclusion on the EPBC Act threatened species list in the Endangered category and

2) the necessary conservation actions for the above species.

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 either by email to: [email protected]

or by mail to:

The DirectorSpecies Information and Policy Section, Wildlife, Heritage and Marine DivisionDepartment of the Environment and EnergyPO Box 787Canberra ACT 2601

Varanus mertensi (Mertens’ Water Monitor) consultation document of 18

mailto:[email protected]

Responses are required to be submitted by Friday 14 May 2021.

Contents of this information package PageGeneral background information about listing threatened species 2Information about this consultation process 3Draft information about the common name and its eligibility for listing 4Conservation actions for the species 13References cited 16Collective list of questions – your views 15

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: http://www.environment.gov.au/biodiversity/threatened/index.html.

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.environment.gov.au/system/files/pages/d72dfd1a-f0d8-4699-8d43-5d95bbb02428/files/tssc-guidelines-assessing-species-2018.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: http://www.environment.gov.au/biodiversity/threatened/nominations.html.

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: http://www.environment.gov.au/biodiversity/threatened/recovery.html.

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


http://www.environment.gov.au/biodiversity/threatened/recovery.html

http://www.environment.gov.au/biodiversity/threatened/nominations.html

http://www.environment.gov.au/system/files/pages/d72dfd1a-f0d8-4699-8d43-5d95bbb02428/files/tssc-guidelines-assessing-species-2018.pdf

http://www.environment.gov.au/system/files/pages/d72dfd1a-f0d8-4699-8d43-5d95bbb02428/files/tssc-guidelines-assessing-species-2018.pdf

http://www.environment.gov.au/biodiversity/threatened/index.html

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’. 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.

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: http://environment.gov.au/privacy-policy .

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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Varanus mertensi Mertens’ Water Monitor

TaxonomyConventionally accepted as Varanus mertensi (Glauert 1951). The species was previously known in Queensland as the Australian Bulliwallah, Varanus bulliwallah (Worrell 1956).

Species Information

DescriptionMertens’ Water Monitor is a medium to large sized semi-aquatic monitor lizard up to 1 m in size. It is dark brown to black on the back with numerous small dark-edged cream or yellow spots. The lower lip is yellowish, speckled or barred with grey. The under surface is white to yellowish with some grey patterning on the throat and chest. The tail is very strongly compressed laterally, to provide power when swimming, has a strong two-keeled crest along the top and is about 1.5 times as long as the head and body (Ward 2012).

Distribution

Mertens’ Water Monitor occurs across the far northern waters of coastal and inland Western Australia, the Northern Territory, and central and north western Queensland (Cogger 2014, Figures 1 & 2). In the Kimberley region of Western Australia, extensive island surveys confirmed Mertens’ Water Monitor on only one of 24 islands being Augustus Island (Palmer et al., 2013).

In the Northern Territory, Mertens’ Water Monitor has been recorded on Marchinbar, Guluwuru and Jigari Islands (Woinarski et al., 1999), Melville and Bathurst Islands in the Tiwi islands (Woinarski et al., 2003), Groote Eylandt and Vanderlin and Winchelsea Islands (ALA 2020). Historically the southern distribution of Mertens’ Water Monitor reached as far as Bulliwallah Station on the Belyando River in central Queensland (Worrell 1956). In summary, surveys of more than 66 islands in the Kimberley and Northern Territory, along with unpublished database records, have recorded it on only nine islands, only three of which have an area much greater than 200 km2 (Palmer et al., 2013, Woinarski et al., 1999).

Cultural Significance

Australian reptiles, particularly predatory species such as monitors, are important components of the environment and wider food chain and are an important part of culture for indigenous people particularly as food, emblems and in storytelling.

Bininj Kunwok is a collective name for the dialect chain that includes Kunwinjku, Kundjeyhmi, Kuninjku, Kune, Mayali and Kundedjnjenghmi. These languages are spoken in the Kakadu and West Arnhem Land regions of the Northern Territory's Top End (Australian Government 2020). In Kakadu National Park and western Arnhem Land, the most common name for Mertens’ Water Monitor is burarr. In Kune dialect it is djarrkka which is the same word used by Burarra speakers (though spelt jarrka in Burarra) for the generic name for goannas.

For Walpiri people in the far north of their range in the Northern Territory, Jarrampayi is the traditional name for Mertens’ Water Monitor and the species is an important food source (Nangalarlu 2014). For Jawoyn people around Katherine Gorge, jutja is the traditional name (Gosler et al., 2013). On the Groote Archipelago, the Warnindhilyagwa people’s traditional name for the species is Dubulkuma (DENR 2019).

This consultation seeks to gather further information on the cultural significance of Mertens’ Water Monitor.


Relevant Biology/EcologyMertens’ Water Monitor is a semi-aquatic lizard usually found basking on rocks, logs, trees and branches overhanging rivers, swamps and lagoons. It inhabits watercourses, billabongs, springs and soaks within its geographical distribution. The species also inhabits human-made water bodies such as dams and irrigation channels (Mayes et al., 2005).

Mertens’ Water Monitor feeds largely on fish, freshwater crabs, frogs and carrion, as well as insects and terrestrial vertebrates (Cogger 2014, Shine, 1986, Losos and Green 1988, Mayes et al., 2005). Freshwater crabs (Holthuisana spp) were the predominant diet of Mertens’ Water Monitor reported in two studies (Mayes et al. 2005, Shine 1986). Its diet is sufficiently general to enable it to adapt to seasonal and spatial differences in prey availability, and is one reason for its widespread distribution in the wet–dry tropics of Australia (Mayes et al., 2005).

Mertens’ Water Monitor constructs a relatively shallow and simple nesting burrow close to water bodies, ranging from right on the water’s edge in the banks of irrigation channels, farm dams, and waterholes and in rock crevices to 150 m away from the water’s edge (Rhind et al., 2016, Mayes et al., 2005), possibly with vegetation lining the nest chamber (Swanson 1976).

Mertens’ Water Monitor found in irrigation waterbodies have been observed to move over large areas, up to 31.8 ha. The greatest daily distance moved along an irrigation channel by the species was over 2.5 km with daily activity areas of between 0.1 – 1 ha (Mayes et al., 2005).

In the Ord River Irrigation Scheme and surrounding East Kimberley/Victoria River Downs bioregion of Western Australia, females lay their eggs during the early dry season. Dry season egg deposition combined with an incubation time of 9-10 months culminates in hatchlings emerging during the following wet season. Individuals display different behaviour during the two seasons, with extensive aquatic activity and minimal basking throughout the day during the wet season and less aquatic activity supplemented with extensive basking periods during the dry season (Mayes et al., 2005). This aligns with observations made by Shine (1986) in the Northern Territory.

The species generation length is not known with certainty, but it is thought likely that animals reach sexual maturity at 3-4 years and live for 10-12 years (Shea et al., 2018). For the purposes of this assessment and that used by other assessments (Shea et al., 2018, Chapple et al., 2019), generation length is assumed to be 6 years.

ThreatsThe preferred habitat of Mertens’ Water Monitor overlaps with that of the cane toad. Mertens’ Water Monitor is fatally poisoned when it consumes cane toads. Smith and Phillips (2006) estimated that 86% of the Australian range of Mertens’ Water Monitor will be encompassed by the predicted range of the cane toad. Mapping by the Department of Agriculture, Water and the Environment using Kearney et al (2008) modelling suggests 100% of the Merten’s Water Monitor modelled distribution will be invaded by the cane toad (Figure 1). Currently, toads have colonised all Mertens’ Water Monitor areas in Queensland, the Top End of the Northern Territory and are currently moving across the Kimberley region covering an estimated 88% of the distribution of Mertens’ Water Monitor. Further declines in Mertens’ Water Monitor are expected to occur when the toad arrives into these areas.

Table 1: Threats impacting Mertens Water Monitor, based on available evidence.

Threat factor

Threat type and status

Evidence base

Invasive species

Cane toad invasion

Known, current

Severe. Mertens Water Monitor was formerly very common, but now only occasional animals are encountered in areas where cane


toads exist. There has been a decline of more than 30% in the Northern Territory and in some areas as high as 93% (Doody et al., 2009) over the past 15 years, due to predation on the cane toad. Two of three studies of subpopulations in the Kimberley and the Northern Territory (Doody et al., 2013, 2014) reported declines of 84-93% within 3-4 years following cane toad invasion, with the third reporting declines of 41% over three years compared with numbers recorded in the two years preceding introduction (Doody et al., 2015). In every case, declines were either ongoing at the end of the study period or, in the Daly River study, may have been levelling off at densities close to zero (Doody et al., 2013, J. Woinarski pers. comm. 2017 in Shea et al., 2018).

Predation by feral pigs

suspected current

Moderate. Clutches of eggs may be predated on by feral pigs and, possibly, wild dogs; and such predation may inhibit population recovery (Woinarski & Winderlich 2014).

Habitat degradation and loss

Habitat change

Suspectedcurrent

Moderate. Agriculture and biological resource use present the most common threats to terrestrial reptiles globally (Tingley et al., 2019). Large areas of this species range are expected to experience intensified development pressure in the next decade (Commonwealth of Australia 2015). Of particular threat will be changes to natural hydrology and riparian habitats utilised by this species.

Mortality

Fire Not well known. High intensity fires may reduce quality of riparian habitat (Woinarski & Winderlich 2014).

Assessment of available information in relation to the EPBC Act Criteria and Regulations

Criterion 1. Population size reduction (reduction in total numbers)Population reduction (measured over the longer of 10 years or 3 generations) based on any of A1 to A4

Critically EndangeredVery severe reduction

EndangeredSevere reduction

VulnerableSubstantial reduction

A1 ≥ 90% ≥ 70% ≥ 50%A2, A3, A4 ≥ 80% ≥ 50% ≥ 30%A1 Population reduction observed, estimated, inferred or

suspected in the past and the causes of the reduction are clearly reversible AND understood AND ceased.

A2 Population reduction observed, estimated, inferred or suspected in the past where the causes of the reduction may not have ceased OR may not be understood OR may not be reversible.

A3 Population reduction, projected or suspected to be met in the future (up to a maximum of 100 years) [(a) cannot be used for A3]

A4 An observed, estimated, inferred, projected or suspected population reduction where the time period must include both the past and the future (up to a max. of 100 years in future), and where the causes of reduction may not have ceased OR may not be understood OR may not be reversible.

(a) direct observation [except A3]

(b) an index of abundance appropriate to the taxon

(c) a decline in area of occupancy, extent of occurrence and/or quality of habitat

(d) actual or potential levels of exploitation

(e) the effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites

In 2017, Mertens’ Water Monitor was included in the Endangered category of the IUCN Red List of Threatened Species under Criterion A4be. An assessment by Chapple et al., (2019) in The


based on any of the followi

Action Plan for Australian Lizards and Snakes 2017 also concluded it was eligible as Endangered under Criterion A4be. This assessment for listing under the EPBC Act follows that of Chapple et al., (2019).

The generation length of Mertens’ Water Monitor is not known with certainty, but it is thought likely that species reaches sexual maturity at 3-4 years and lives for 10 -12 years (Shea et al., 2020). For the purposes of this assessment, generation length is assumed to be around 6 years thus three generations being 18 years and longer than 10 years. Long term monitoring of the impacts of cane toads on Mertens’ Water Monitor which has provided an index of abundance appropriate to the taxon, currently spans 12 years post cane toad invasion, hence the application of Criterion A4be given the cane toads continuing and irreversible spread across the remainder of the species range into the near future.

Mertens’ Water Monitor is projected to undergo a decline of more than 50%, and possibly up to 80%, over a three-generation period due to the impacts of invasive cane toads, which have expanded their range to encompass the majority of the mainland range of this species. These impacts have not ceased and cane toad invasion is not reversible. There has been little or no recovery of subpopulations once Cane Toads are established within an area, and there have been anecdotal reports of complete local extinction with no evidence of recolonization (Chapple et al., 2019).

Initially an 18-month study at Manton Dam Recreation Area reported evidence of rapid decline in both abundance and site occupancy of Mertens’ Water Monitor eight months after cane toads reached this area, and an overall decline in abundance by nearly 80% between December 2004 and May 2006 (Griffiths and McKay 2007). Comparable rates of decline (84-93%) within three years of the Cane Toad's arrival have been reported in subsequent multi-year studies of newly-colonized sites in the Northern Territory (Doody et al., 2009, 2014), and of almost 41% over a comparable period in Kununurra in the north-eastern Kimberley (Doody et al., 2015). The most recent follow up monitoring by Doody et al., (2017) at the two sites on the Daly River, NT, discovered Mertens’ Water remained at low abundances between the shorter-term and medium-term studies. In summary, four populations have been monitored in the NT and WA and all but one (41% decline) underwent >50% decline and two underwent >80% decline within the past two generations with a projected continuing decline due to continued poisoning from cane toads.

Although island subpopulations exist that may provide toad-free refugia, this species is found on relatively few offshore islands (surveys of more than 66 islands in the Kimberley and Northern Territory, along with unpublished database records, have recorded it on only nine, only three of which have an area much greater than 200 km2 (Palmer et al., 2013, Woinarski et al., 1999). In total, these islands represent less than 1% of this species' extent of occurrence (J. Woinarski pers. comm. 2017 in Shea et al., 2018).

Addressing anecdotal reports of recovery

Cane Toads have become established in the majority of the species' mainland range and are projected to invade most of the remainder within three generations (J. Woinarski pers. comm. 2017 in Shea et al., 2018). As such, rates of global population decline in three generations could be in excess of 80%. As no studies have extended beyond three years following cane toad introduction, and declines were ongoing at both sites where the population remained sufficiently large to estimate a population trends, this rate of decline could be an underestimate (J. Woinarski pers. comm. 2017 cited in Shea et al., 2018), and it is not clear whether subpopulations in areas where the toad has been long-established have stabilized. There are reports that there is "very clear evidence" of recovery in the Top End of the Northern Territory, including regular anecdotal reports of local population increases and regular sightings at sites where the species apparently declined following toad invasion (Shea et al., 2018).

Observations spanning a ten year period in the Top End also suggest population recovery in this area and there have been reports that the species persists in "healthy numbers" in the Daly Waters and Barkley regions, suggesting that the species may not have been subject to significant declines in southern parts of its range (Shea et al., 2018). The species also now


appears to be quite common in northern Queensland, where Cane Toads are long-established (Shea et al., 2018). A complete recovery is unlikely in toad-impacted areas; reports from areas of Queensland where the cane toad has been present since the 1950s suggest that, while Mertens’ Water Monitor had recovered to "moderate numbers" in at least one area in Cape York as long ago as 1960, monitor numbers remain lower than they were prior to toad invasion long after toad populations had stabilized (at a much lower level) (H. Cogger pers. comm. 2017 in Shea et al., 2018). The species is nevertheless now "quite common" in North Queensland (E. Vanderduys pers. comm. 2017 in Shea et al., 2018) and the Top End, based in the latter case on observations over a ten-year period (M. Greenlees pers. comm. 2017 in Shea et al., 2018). Opportunistic observations in the Arnhem Highway area at two-year intervals over six years suggest that the species has gradually recovered to a point where it can now be detected at around 25% of its historical sites (M. Greenlees pers. comm. 2017 in Shea et al., 2018).

Despite these anecdotal reports, the most credible monitoring undertaken for the species by Doody et al (2015, 2017) report no reliable evidence of recovery following cane toad invasion in any studied subpopulation, and that reports of possible recovery are based on anecdotal observations rather than systematic sampling, and may be biased by the conspicuous nature of surviving animals basking near water bodies, which represent a small proportion of the population (Mayes 2006, Griffiths and McKay 2007). It is appropriate to exercise caution against the assumption that repeated anecdotal sightings of Mertens’ Water Monitor at a site reflects a population either not impacted by toads or is in recovery, given that all three studies investigating impacts have quantified severe declines (J. Woinarski pers. comm. 2017 cited in Shea et al., 2018).

Evidence:The data presented above appears to demonstrate that the species is eligible for listing as Endangered under Criterion A4be. However, the purpose of this consultation document is to elicit additional information to better understand the species’ status. This conclusion should therefore be considered to be tentative at this stage, as it may be changed as a result of responses to this consultation process.

Criterion 2. Geographic distribution as indicators for either extent of occurrence AND/OR area of occupancy

Critically Endangered

Very restricted

EndangeredRestricted

VulnerableLimited

B1. Extent of occurrence (EOO) < 100 km2 < 5,000 km2 < 20,000 km2

B2. Area of occupancy (AOO) < 10 km2 < 500 km2 < 2,000 km2

AND at least 2 of the following 3 conditions indicating distribution is precarious for survival:

(a) Severely fragmented OR Number of locations = 1 ≤ 5 ≤ 10

(b) Continuing decline observed, estimated, inferred or projected in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) area, extent and/or quality of habitat; (iv) number of locations or subpopulations; (v) number of mature individuals

(c) Extreme fluctuations in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) number of locations or subpopulations;( iv) number of mature individuals

Evidence:The extent of occurrence of Mertens’ Water Monitor is 1,769,960 km2 and current area of occupancy is 936 km2 (based on records from 2000-2020; see Figures 1&2). The population has been subject to a net decline in the number of mature individuals (Doody et al., 2009, 2013, 2017) and has a projected continuing decline due to continued poisoning from cane toads. The EOO was calculated using a minimum convex hull, and the AOO calculated using a 2x2 km grid cell method, based on the IUCN Red List Guidelines (IUCN 2019).


Given the Mertens’ Water Monitor remains present at low densities throughout its range (Shea et al., 2018) and its large and generally unsurveyed distribution, it is not considered to be severely fragmented. The aquatic nature of the species, particularly its ability to swim and the connectivity of its preferred habitat across the Top End of Australia, suggests that the species has the ability to disperse.

The key threat to Mertens’ Water Monitor, cane toads, is modelled to eventually cover the entire known range of the species (See Figure 2). Some areas, primarily offshore islands, may remain unaffected if strong biosecurity efforts remain or are put in place (see Figure 1). Figure 2 shows that only 12% of the Mertens’ Water Monitor modelled distribution is currently toad free however the population has a projected continuing decline due to poisoning from cane toads and also remain vulnerable to other threats of habitat loss and degradation from development and egg predation by feral animals. This prevailing threat has been demonstrated to rapidly affect all individuals of the taxon present, which means that all mainland occurrences of the Mertens’ Water Monitor could be considered one location, with each of the nine known island sub-populations representing a separate population with independent probabilities of the introduction of cane toads. In total the number of locations is 10, meeting sub-criterion B2a.

The data presented above appear to demonstrate that Mertens’ Water Monitor, with a AOO of 936 km2, ≤10 locations and an observed and projected continuing decline in area of occupancy and number of mature individuals is eligible for listing as Vulnerable under Criterion B2ab(ii,iv,v). However, the purpose of this consultation document is to elicit additional information to better understand the species’ current Area of Occupancy and number of locations, particularly where cane toads are and have been for some time. This conclusion should therefore be considered to be tentative at this stage, as it may be changed as a result of responses to this consultation process.


Figure 1. The modelled distribution of Mertens’ Water Monitor (Varanus mertensi) shown with observations between 2000-2020 and the current modelled extent of the cane toad’s spread in Northern Australia


Figure 2. The modelled distribution of Mertens’ Water Monitor (Varanus mertensi), AOO and EOO calculations overlayed with the anticipated spread of cane toads in Northern Australia based on Kearney et al (2008).

Criterion 3. Population size and declineVaranus mertensi (Mertens’ Water Monitor) consultation document

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Critically Endangered

Very low

EndangeredLow

VulnerableLimited

Estimated number of mature individuals < 250 < 2,500 < 10,000

AND either (C1) or (C2) is true

C1 An observed, estimated or projected continuing decline of at least (up to a max. of 100 years in future)

Very high rate25% in 3 years or 1

generation(whichever is longer)

High rate20% in 5 years or 2

generation(whichever is

longer)

Substantial rate10% in 10 years or 3

generations(whichever is

longer)

C2 An observed, estimated, projected or inferred continuing decline AND its geographic distribution is precarious for its survival based on at least 1 of the following 3 conditions:

(a)

(i) Number of mature individuals in each subpopulation ≤ 50 ≤ 250 ≤ 1,000

(ii) % of mature individuals in one subpopulation = 90 – 100% 95 – 100% 100%

(b) Extreme fluctuations in the number of mature individuals

Evidence:There are no data on total population sizes. The data available and presented to demonstrate the species decline in Criterion 1 is insufficient to demonstrate if the species is eligible for listing under this criterion. However, the purpose of this consultation document is to elicit additional information to better understand the species’ status. This conclusion should therefore be considered to be tentative at this stage, as it may be changed as a result of responses to this consultation process.

Criterion 4. Number of mature individuals Critically

EndangeredExtremely low

EndangeredVery Low

VulnerableLow

Number of mature individuals < 50 < 250 < 1,000

Evidence:There are no data on total population sizes. The data available and presented to demonstrate the species decline in Criteria 1 is insufficient to demonstrate if the species is eligible for listing under this criterion. However, the purpose of this consultation document is to elicit additional information to better understand the species’ status. This conclusion should therefore be considered to be tentative at this stage, as it may be changed as a result of responses to this consultation process.

Criterion 5. Quantitative Analysis Critically Endangered

Immediate futureEndangeredNear future

VulnerableMedium-term future

Indicating the probability of extinction in the wild to be:

≥ 50% in 10 years or 3 generations,

whichever is longer (100 years max.)

≥ 20% in 20 years or 5 generations,

whichever is longer (100 years max.)

≥ 10% in 100 years


Evidence:There is no quantitative analysis of overall population size. Population viability analysis appears not to have been undertaken, there are insufficient data to demonstrate if the species is eligible for listing under this criterion. However, the purpose of this consultation document is to elicit additional information to better understand the species’ status. This conclusion should therefore be considered to be tentative at this stage, as it may be changed as a result of responses to this consultation process.

Recovery PlanA decision about whether there should be a recovery plan for this species has not yet been determined. The purpose of this consultation document is to elicit additional information to help inform this decision.

Conservation ActionsCane toads have proven too prolific to eradicate or control with no feasible or cost-effective management prescriptions to address the threat (Ward 2012, Doody et al., 2017, House of Representatives Standing Committee on the Environment and Energy 2019). Recovery success for Mertens’ Water Monitor would however be greatly enhanced by the uptake of recommendations from the recent parliamentary inquiry into controlling the spread of cane toads (House of Representatives Standing Committee on the Environment and Energy 2019).

It has been suggested that recovery of Mertens’ Water Monitor must occur unassisted by evolutionary means i.e. through dispersal into extirpated sites from surviving populations with alleles for toxin resistance or toad avoidance (Doody et al., 2017). Conservation and management effort in the interim is best aimed at trying to maintain surviving depleted populations in toad-invaded areas (Ward 2012).

Aversion learning prescribed and undertaken for other cane toad impacted species such as the Northern Blue-tongue Lizard (Tiliqua scincoides intermedia) and the Northern Quoll (Dasyurus hallucatus) are not considered an appropriate conservation action for this species. Although recent research proposes that these lizards could be ‘taught’ to avoid toads through aversion learning (Ward-Fear et al., 2016), cultural inheritance is highly unlikely because parents abandon eggs which precludes teaching offspring to avoid toads (Doody et al., 2017). Thus if 90% of lizard parents die while attempting to ingest cane toads, a similar percentage of their offspring would be expected to similarly perish. Aversion learning would provide a conservation tool that would only provide protection for a (small) group of one generation of lizards. Rather, these predators are faced with recolonizing on their own, presumably after they have either evolved behavioural avoidance of, or toxin resistance to, cane toads (Doody et al., 2017).

The only way to validate recovery is through longer-term study of populations with both baseline densities and immediate post-invasion densities. Unambiguous recovery of the Mertens’ Water Monitor population remains undemonstrated and will require long-term population monitoring before and after toad invasion (Doody et al., 2017). The above context has informed the primary conservation actions for this species.

ObjectiveThis Conservation Advice for the Mertens’ Water Monitor adopts the objective set for the species by Woinarski & Winderlich (2014) in the Kakadu Threatened Species Strategy 2014-2024. The objective for Mertens’ Water Monitor is for a population stable or increasing over three successive monitoring episodes by 2025.

Primary Conservation Actions Establish or maintain a program of effective quarantine, adequate surveillance and early

response measures to ensure that offshore islands where this species occurs remain free of toads in the long term.


Ongoing monitoring of remnant populations to identify/quantify recovery or further decline.

Trial establishing 'ark' populations of individuals either in captivity or on offshore islands , ensuring this is preceded with an assessment of any impacts on likely prey species and includes monitoring.

Engage with Traditional owners including Aboriginal Land Councils, the Indigenous Protected Area Network, ranger groups and private land managers or organisations to increase awareness and undertake survey, monitoring and management effort for the Mertens’ Water Monitor.

Through the above actions identify important populations of Mertens’ Water Monitor to create a multijurisdictional network of sites for conservation and management.

Conservation and Management prioritiesInvasive species

Ensure where achievable, quarantine, surveillance and rapid response programs for toad free islands where Mertens’ Water Monitor populations exist include;

o Pathway risk assessments to identify primary vectors and points of entry.o Development of quarantine procedures at all freight and passenger

embarkation ports.o Construction of robust, fit-for-purpose, cane toad barriers at main freight portso Employment of a quarantine officer with a trained toad detection dog. o Inspections of all arriving craft and freight.o Establishment of cane toad traps and regular surveillance surveys at ports,

settlements and potential waterbodies near potential arrival points.o Awareness and education campaigns, including professional staff induction,

school education programs, public billboards and broadcasts on all commercial flights to islands.

Manage and protect important populations of Mertens’ Water Monitor in areas not currently affected by cane toads to halt population declines.

Implement mechanisms for local-scale eradication (or exclusion) of cane toads, or prevention of toad colonisation.

Implement control measures to reduce the abundance of wild pigs and dogs across the species distribution.

Habitat loss, disturbance and modifications

Protect and prevent impacts to habitat critical to the survival of the species in the planning, construction and post construction phases of future developments. Important components of this action are:

o promoting and educating stakeholders in the application of the assessment and approval process under the EPBC Act and their obligations under the Act to avoid significant impacts to Mertens’ Water Monitor.

o ensuring loss of habitat is avoided and connectivity is maintained between and within populations through appropriate siting of infrastructure and revegetation and management of riparian habitat.

o ensuring hydrological impacts are well understood and considered in assessment and mitigation.

Fire


The appropriate fire regime for Mertens’ Water Monitor is not well known. Relatively low intensity patchy burning regime may be appropriate (Ward 2012).

Where information and knowledge exist on preferred fire regimes for Mertens’ Water Monitor or its habitat, ensure where possible that Healthy Country Plans and or Indigenous Protected Area Management Plans identify the needs and actions for the species as they relate to fire activities.

Stakeholder Engagement Engage with traditional owners, private landholders and government staff to educate

them about the ecology and habitat requirements of Mertens’ Water Monitor and its key threats to ensure key populations are appropriately protected and managed across large landscapes.

Engage interested nature conservation, land management and land holder groups in conservation management activities, such as survey and monitoring, and feral animal management. Use workshops to aid stakeholders in developing the skills and knowledge required to manage this species.

Survey and Monitoring priorities Continue monitoring invaded sites for at least a decade to test hypotheses about

recovery. Target monitoring of populations where cane toads have long occupied the habitat. Identify priority monitoring sites for the species based on unlikely colonisation of cane

toads.

Information and Research priorities Assess population-level impacts of predation on eggs by wild pigs, and mechanisms that

may reduce such losses.

Investigate potential genetic resistance to cane toad toxin in relictual individuals from sites with varying history of cane toad occupancy.

Document population structure and identify genetically distinct/important populations through analysis of existing tissue samples or collection of tissue samples from remaining populations.

Collective list of questions – your views

1. Do you have any additional information in regard to the ecology or biology of the species?

2. Can you provide additional information on the range or location of populations? For example, information on local population increases and regular sightings at sites where the species declined following toad invasion.

3. Do you have further information on the threats that face the species?

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

5. Do you have any information on the preferred fire regimes for this species?

6. Are you aware of other knowledge (e.g. traditional ecological knowledge) that may help better understand the species?

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


8. Do you have any information on what is likely to constitute habitat critical to the survival of this species?

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

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