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Water Mouse (Xeromys myoides)

The water mouse is a small, nocturnal native rodent of coastal mangroves, saltmarshes, sedgelands and nearby freshwater wetlands in Queensland and the Northern Territory, with records from Papua New Guinea. It is vulnerable nationally and in Queensland, and development can harm it through clearing, fragmentation, altered tidal or freshwater flows, loss of nest sites and increased predator access.

Conservation status

Commonwealth, EPBC Act 1999: Vulnerable.

Queensland, Nature Conservation Act 1992: Vulnerable.

Breeding season

The water mouse may breed in any month, so there is no reliably safe seasonal window for clearing occupied habitat. Records from south-east Queensland indicate periods when pregnancy, enlarged nipples and juveniles were observed, but breeding data are sparse and should be used with site evidence.

Survey and clearing decisions should be based on current habitat assessment and signs of recent activity, not season alone. The supplied documents do not establish a period when breeding or dependent young are absent.

  • Breeding: Breeding may occur throughout the year. Pregnant females were recorded in January, May, August, September and October, while enlarged nipples were recorded from July to December.
  • Young: Juveniles were recorded in May, July, August and November. Young may be present at other times because breeding can occur throughout the year.
  • Nightly movement and foraging: The species is primarily nocturnal and may travel up to 2.9 to 3 km in a night. In south-east Queensland it has been observed moving with the receding tide between sedgelands and mangroves.
  • Nest and refuge use: Nests provide refuge from high tides and predators and may be used by successive generations over several years.
  • Highest clearing risk: Treat all months as high risk because breeding may occur throughout the year and nests are used for breeding and refuge. Risk is especially high wherever active mounds, hollows, banks or recent middens are present.

Identification

The water mouse is a small, rat-sized rodent with a distinctive dark upper coat and white underside. It is most often detected from nests, middens and targeted night trapping rather than casual daytime sightings.

Adults have short, very dense and silky slate-grey fur above and a pure white belly. Some Queensland adults have white dorsal spotting, while old animals may become grizzled with a rufous wash on the flanks.

The ears are short and rounded, the eyes are very small, the hindfeet are not webbed, and the tail is slender, thinly haired and finely ringed. A strong musty odour may be noticeable at close range.

Maximum head and body length: 126 mm

Maximum weight: 64 g

Average weight: About 41 g

Identification: Similar species

The water mouse is much smaller than the sympatric water rat, Hydromys chrysogaster. It lacks the water rat's partially webbed hindfeet and distinctive white-tipped tail.

It can be separated from the black rat, Rattus rattus, by its short ears, sleek grey dorsal fur, white belly and tail that is not significantly longer than the head and body.

Identification: Field signs

Nest mounds are the most distinctive field sign. They may be free-standing, built against mangrove roots or trunks, placed on small elevated islands in the tidal zone, made in supralittoral banks, or formed in human-created spoil heaps.

Mounds are commonly about 20 to 60 cm high, with a basal circumference of about 1.6 to 4.8 m and one to three entrance holes. Fresh mud plastering, mud tracks, vegetation, leaves, sedges and crab shells can indicate recent use.

Small middens containing crab, mollusc and other marine invertebrate remains may occur inside or outside hollow trees and near nests. The species may also use tree hollows, banks, fallen timber and simple burrows, so the absence of a mound does not exclude it.

The supplied sources do not provide diagnostic descriptions of tracks, scats, calls or eyeshine. Elliott trapping at night is the only method identified as reliable for estimating population density.

Daytime search effort: One to two hours searching for nests per hectare of intertidal or supralittoral potential habitat

Daytime transects: Transects spaced 50 to 100 m apart, or quadrats

Elliott trapping effort: At least 400 trap nights per 4 to 5 ha of potential habitat

  • Search systematically for active-looking mounds, fresh mud, entrances, mud pathways and prey middens during daytime habitat searches.
  • Treat hollow mangrove trunks, supralittoral banks, fallen timber and spoil heaps as potential shelter sites during clearing inspections.
  • Use a suitably qualified mammal surveyor for targeted detection work.

Distribution: Australian range

The Australian distribution is patchy and concentrated in near-coastal wetlands. Records represent disjunct populations in Queensland and the Northern Territory, with an additional record area in south-west Papua New Guinea.

In Queensland, the species is recorded from near the Queensland and New South Wales border north to the Proserpine area. Important recorded areas include the south-east Queensland coast, Moreton Bay, Pumicestone Passage, Bribie Island, North and South Stradbroke Islands, Fraser Island, the Great Sandy Strait, and the central south Queensland coast from Agnes Water to Cannonvale.

In the Northern Territory, records are widely separated and include the Glyde River and Tomkinson River areas of Arnhem Land, the South Alligator River and Kakadu area, the Daly River floodplain and Melville Island. The species has also been recorded from the Bensbach River floodplain in south-west Papua New Guinea.

Queensland range: Near the Queensland and New South Wales border to Proserpine

Northern Territory range: Coastal sites from Arnhem Land to the Daly River floodplain, including Melville Island

Broad regional setting: Patchily distributed in near-coastal intertidal and freshwater wetland systems

Distribution: Strongholds and subpopulations

Recorded Queensland areas include the Great Sandy Strait and Fraser Island area, Moreton Bay and its islands, the Maroochy River area, Bribie Island, central Queensland coastal sites and parts of the Gold Coast region. Some sites occur in protected areas, including Great Sandy National Park, Bribie Island National Park, Cape Palmerston National Park and Cape Hillsborough National Park.

Genetic work identified distinct subpopulations, with relatively high genetic diversity in central Queensland and very low diversity in the Coomera region. A Coomera subpopulation became locally extinct after decline associated with a nearby canal and housing development.

Distribution: Population size and trend

There is no reliable national population estimate or integrated monitoring programme. Available assessments indicate continuing decline in Australian mature individuals and subpopulations, although survey effort has expanded the known Queensland distribution.

The Queensland estimate in the background material is older and has low precision. It should not be used as a site population estimate.

Estimated Queensland population: About 1,001 to 10,000 individuals in an estimated 101 to 1,000 km², based on an older assessment

Estimated Australian mature individuals: About 10,000, with low reliability

Estimated range-wide mature individuals: About 5,000 to 50,000, with 10 to 30 subpopulations

Population trend: Thought to be declining in Australia; local declines and extirpation have been recorded

Habitat: Habitat types

Water mouse habitat is usually a connected set of intertidal and coastal freshwater habitats rather than a single vegetation type. Intact hydrology, prey resources and dry shelter above regular inundation are important site attributes.

The species uses mangrove communities and associated saltmarsh, saline grassland, sedgeland, clay pans, coastal heathland and freshwater wetlands. It may occur where mangroves, supralittoral banks and nearby freshwater wetlands form a connected habitat complex.

Northern Territory records include mangrove forests, saltmarsh, sedgelands, saline clay plains, freshwater lagoons and Melaleuca wetlands. Queensland records include high intertidal mangrove forest, saline grassland, freshwater swamps, wet heath and restiad swamp.

Habitat: Vegetation and structure

Queensland mangrove habitat may include Avicennia marina, Rhizophora stylosa, Bruguiera gymnorrhiza, Aegiceras corniculatum and Ceriops tagal. Upper tidal areas may support Juncus kraussii, Baumea juncea, Baumea rubiginosa, Fimbristylis ferruginea and Sporobolus virginicus.

Adjacent freshwater or terrestrial communities may include Melaleuca quinquenervia, Corymbia intermedia, Casuarina glauca, Eucalyptus robusta, Leptospermum liversidgei, Gahnia sieberiana, Caustis blakei, Banksia and Persoonia.

Important microhabitats include tidal pools, channels, crab holes, pneumatophores, root crevices, hollow and fallen timber, driftwood and suspended accumulations of twigs and leaves.

Habitat: Hydrology and site limits

The species requires intact hydrology, including suitable tidal inundation, freshwater flows, salinity and water quality. It uses both intertidal and freshwater habitats, and habitat suitability varies between the Northern Territory, central south Queensland and south-east Queensland.

The supplied documents do not provide an elevation limit or a defined climatic threshold. Records are concentrated in coastal and near-coastal areas, including coastal floodplains and wetlands close to fore dunes.

  • Map and ground-truth mangroves, saltmarsh, sedgelands, supralittoral banks and nearby freshwater wetlands before designing clearing limits.
  • Maintain natural tidal connections, overland flows, freshwater inputs and water quality during construction.

Foraging habitat: Diet and prey

The water mouse feeds mainly on small marine and intertidal invertebrates, especially crabs. It forages through mangroves and adjacent saltmarsh or sedgeland, often moving with the receding tide.

Recorded prey includes grapsid crabs, mud lobster, shore crabs, marine polyclads, marine pulmonates and marine bivalves. Northern Territory nest material and middens included grapsid crab remains.

Plant foods have not been reported, although gut morphology suggests that the diet may not be entirely carnivorous.

Main food group: Marine and freshwater invertebrates, particularly crabs

Recorded prey: Grapsid crabs, mud lobster, shore crabs, marine pulmonates, polyclads and bivalves

Foraging habitat: Foraging areas and movement

In south-east Queensland, the most productive zone studied was between nests on the supralittoral bank and the first 100 m into the mangroves. Animals have been observed following the receding tide through sedgelands and into mangroves.

The species may travel up to 2.9 to 3 km in a night while crossing a home range. Reported average home ranges are about 0.64 to 0.7 ha, with male and female estimates of about 0.77 ha and 0.53 ha respectively at one study site. A separate site had a mean home range of 3.42 ha.

Nightly travel: Up to 2.9 to 3 km

Typical average home range: About 0.64 to 0.7 ha

Recorded sex difference: Male average home range 0.77 ha; female average 0.53 ha at North Stradbroke Island

  • Protect the full foraging connection between nest sites, supralittoral margins, saltmarsh or sedgeland and mangrove prey habitat.
  • Prevent sediment, polluted runoff and salinity changes that reduce crab, mollusc and other invertebrate prey.

Breeding habitat: Breeding biology

Breeding information is limited. Nests can be communal and may be used by successive generations, so an occupied nest mound or hollow should be treated as a breeding site even when young are not seen.

Up to eight animals of both sexes may share a nest mound, although usually only one sexually active male was present in the North Stradbroke Island study. Females may produce up to four young.

Pregnancy, enlarged nipples and juveniles have been recorded in several months, and the species may breed throughout the year. Gestation, age at sexual maturity and lifespan are not known in the supplied documents.

Breeding season: Possibly throughout the year

Litter size: Up to four young

Gestation: Unknown

Age at maturity: Unknown

Lifespan: Unknown

Generation length: Assumed to be 2 to 3 years

Communal nesting: Up to eight individuals recorded in one mound, usually with one sexually active male

Breeding habitat: Breeding habitat

Breeding and refuge nests occur above high tide in free-standing mud mounds, mounds against mangrove trees or roots, mounds on elevated tidal islands, supralittoral banks, hollow trunks and occasionally human-created spoil heaps.

The breeding area needs nearby mangroves, saltmarsh, sedgeland or freshwater wetland that provides invertebrate prey and allows movement between shelter and foraging habitat.

  • Retain nest mounds, supralittoral banks, hollow trees and connected intertidal vegetation within the construction exclusion area.
  • Inspect potential nest habitat before clearing, including elevated dry ground within mangrove communities and the landward edge of the tidal zone.
  • If a nest or recent sign is found, stop work in the immediate area and obtain advice from the relevant wildlife authority and qualified fauna specialists.

Sheltering habitat: Nests and burrows

The water mouse shelters during daylight and between tidal cycles in mud structures, banks, hollows and other elevated refuges. Nests can remain in use for several years and may shelter multiple animals.

Five nest forms are described: free-standing mud mounds or mounds at mangrove bases, mounds on small elevated tidal islands, mounds or holes in supralittoral banks, nests inside hollow tree trunks and nests in human-created spoil heaps.

Mounds are usually 20 to 60 cm high, with a basal circumference of 1.6 to 4.8 m and one to three visible entrance holes. Entrances may occur at the top, side or base, or in adjoining banks and fallen timber.

Fresh mud on top of a mound can show that the structure is being raised above high tide. Mud tracks and a strong odour may indicate recent use.

Typical nest mound height: 20 to 60 cm

Typical basal circumference: 1.6 to 4.8 m

Visible entrances: Usually one to three, although additional entrances may be hidden

Nest persistence: A nest may be used by successive generations over several years

Sheltering habitat: Other shelter features

The species may shelter in hollow mangrove trunks, crevices around roots, fallen timber, supralittoral banks and simple burrows. It is assumed not to need obvious mounds in non-tidal environments.

Small elevated islands, dry supralittoral areas and landward margins of mangroves provide shelter from high tides and may reduce exposure to predators.

  • Do not remove, fill or compact mounds, banks, hollow trees, fallen timber or spoil heaps until they have been assessed for water mouse use.
  • Keep machinery, stock, vehicles and spoil storage away from wetland margins and potential nest structures.
  • Retain connected vegetation between shelter sites and intertidal foraging areas.

Threats: Clearing and fragmentation

Habitat removal and degradation from coastal development are the main threats. Small, fragmented populations can also face increased predator access and loss of prey and nesting opportunities.

Clearing for residential development, resorts, marinas, aquaculture, sand mining, bund walls and utility or transport easements can remove mangroves, saltmarsh, sedgelands, freshwater wetlands, nest mounds and movement links.

Fragmentation reduces feeding resources and nesting opportunities, increases edge effects and weed invasion, and can restrict recolonisation. Local extinction has been recorded beside a Gold Coast canal and housing development.

  • Avoid clearing habitat known or likely to support the species, including connecting supralittoral and intertidal vegetation.
  • Design infrastructure to retain habitat corridors and avoid cutting across the connection between mangroves, saltmarsh, freshwater wetlands and nest sites.
  • Use a natural vegetation buffer of at least 30 m around areas containing or linking likely habitat where impacts cannot be avoided.

Threats: Hydrology, soils and pollution

Stormwater runoff can increase freshwater inflows and sediment loads, alter salinity and reduce crab prey. Runnelling, bund walls, flow-control gates and wetland drainage can change tidal amplitude, inundation frequency and water levels.

Disturbance of acid sulfate soils can release sulphuric acid, iron, aluminium and heavy metals. These changes can degrade vegetation and harm crustaceans, molluscs and other prey. Herbicides, pesticides, mosquito-control chemicals and oil pollution can also affect habitat or prey.

  • Maintain existing tidal flows, freshwater inputs, salinity, drainage patterns and water quality.
  • Prepare and implement acid sulfate soil, erosion, sediment and contaminated runoff controls before earthworks.
  • Prevent construction water and stormwater from entering mangroves, saltmarsh or freshwater wetlands without treatment.

Threats: Predators, vehicles, fire and grazing

Cats, foxes, dogs and pigs may prey on water mice, with fragmentation and urban encroachment likely to increase access. Cattle and other hard-hoofed animals can trample nests, remove cover and alter wetland hydrology.

Recreational vehicles can create ruts, cause saltwater incursion and damage supralittoral vegetation. Boats and personal watercraft can erode banks or wash away mound nests. Fire in supralittoral habitat can destroy nests and cover.

The supplied documents do not identify a disease as a known major threat. Climate change and sea-level rise are expected to reduce habitat extent or quality, but the local effects at a project site require assessment.

  • Fence work areas and retained habitat where needed to exclude livestock, domestic dogs and other introduced animals.
  • Control access by vehicles and vessels to supralittoral banks, saltmarsh and intertidal habitat.
  • Prevent accidental fire and manage fire around nest mounds and supralittoral shelter areas in accordance with local fire requirements.
  • Include pest, weed and hydrology monitoring in the environmental management plan.

Survey methodology: 1. Habitat assessment

Survey the Water Mouse where a project may affect mangroves, saltmarsh, sedgelands, clay pans, supralittoral banks or nearby coastal freshwater wetlands. Use a suitably qualified mammal ecologist, review aerial photographs and topographic maps first, and target elevated, dry areas that may contain nest mounds.

Map mangrove communities, saltmarsh, saline grasslands, sedgelands, clay pans, heathlands and coastal freshwater wetlands within and beside the work area.

Record intact tidal or freshwater hydrology, prey resources, crab middens, tidal pools, channels, crab holes, pneumatophores, tree hollows, fallen timber, driftwood, supralittoral banks and existing nest structures.

Give particular attention to the zone from supralittoral nest sites to the first 100 metres into mangroves in south-east Queensland, where this habitat has been identified as productive for the species.

Known habitat: Mangroves, associated saltmarsh, sedgelands, clay pans, heathlands and coastal freshwater wetlands with suitable prey, nest sites and intact hydrology.

Typical activity: The species is nocturnal and may travel up to 2.9 kilometres in a night across home ranges averaging about 0.7 hectares.

  • Use aerial photographs, topographic maps and available vegetation mapping to identify elevated, dry supralittoral areas before field inspection.
  • Ground truth all habitat units and record the location, condition and likely function of nest sites, feeding areas and movement connections.

Survey methodology: 2. Daytime searches for nests and signs

Search during daylight for nest mounds, burrows, mud plastering, entrances, tracks, feeding middens and other signs. Daylight searches are useful because the species shelters in nests or hollows during the day and is most active at night.

Inspect tree bases, buttress roots, supralittoral banks, small elevated islands, fallen timber, hollow trunks, spoil heaps and other elevated structures.

Recommended spacing: 50 to 100 metre transects.

Recommended search effort: One to two hours per hectare of intertidal or supralittoral habitat.

  • Run transects at 50 to 100 metre intervals, or search representative quadrats across all potentially suitable habitat.
  • Spend one to two hours searching for nesting structures for every one hectare of intertidal or supralittoral Water Mouse habitat.
  • Record fresh mud plastering, vegetation or crab shell in nest material, entrances and distinctive odour as possible evidence of recent nest use.
  • Treat a nest as potentially occupied unless survey evidence and a qualified ecologist support a different conclusion.

Survey methodology: 3. Elliott trapping

Use Size A Elliott traps at night when a population estimate or stronger evidence of presence is required. Elliott trapping is the only method identified in the documents as reliable for estimating Water Mouse population density.

Target traps to suitable habitat identified during the assessment, including mangrove edges, saltmarsh, sedgeland, wetland margins and areas near nest mounds or prey middens.

Trap type: Size A Elliott trap.

Timing: Night.

Minimum effort: 400 trap nights per four to five hectares of potential habitat.

Known home ranges: Average about 0.7 hectares, with reported male and female averages of about 0.8 and 0.6 hectares in south-east Queensland.

  • Provide at least 400 trap nights for every four to five hectares of potential Water Mouse habitat.
  • Bait traps with pilchards cut in half, mullet pieces or commercial cat food.
  • Check traps and manage them in accordance with the approved survey plan, animal welfare requirements and any relevant permit conditions.
  • Record trap locations, dates, weather and tidal conditions, trap effort, captures, non-target animals and evidence of nest use.

Survey methodology: 4. Supplementary detection methods

Use supplementary methods to increase the chance of detection, particularly where trapping access is difficult or where the project may affect a large or fragmented wetland area.

Spotlighting can help detect nocturnal animals, while pitfall trapping and hair tubing can add records. These methods are supplementary and are not required when the primary methods have been completed.

  • Use spotlighting at night with attention to mangrove floors, wetland margins, channels, banks and nest structures.
  • Use hair tubing only where the method is suitable for the site and the equipment can be secured from tides, flooding and non-target animals.
  • Do not treat a negative result from a supplementary method as evidence that the species is absent.

Survey methodology: Minimum effort and reporting

  • Use habitat assessment, daytime searches and night-time Elliott trapping as the primary survey package wherever the species may occur.
  • Adjust survey timing, area and effort if surveys are undertaken in conditions that reduce detection, including unsuitable tide, flooding, heavy rain or restricted access.
  • Have the survey completed or checked by a person experienced in mammal surveys and Water Mouse habitat.
  • Report all records, including nests, middens, captures, photographs and reliable signs, to the relevant Queensland or Northern Territory wildlife database and notify the relevant conservation authority where required.
  • Retain the survey design, effort, raw results, locations, habitat descriptions, weather, tide and limitations in the project environmental records.
  • If the action may have a significant impact, refer it to the Australian Government environment minister before work starts; the minister decides whether EPBC Act approval is required.

Before habitat disturbance: Avoid and minimise impacts

Treat any suitable coastal wetland or intertidal habitat within the species' known or potential range as a survey and planning issue. The main project risks are habitat removal, fragmentation, altered hydrology, damage to nests and banks, pollution, weeds, fire, livestock and introduced predators.

Retain mangroves, saltmarsh, saline grasslands, sedgelands, clay pans, supralittoral banks and nearby coastal freshwater wetlands where they provide nest sites, prey or movement connections.

Keep tidal and freshwater flows, salinity, inundation patterns and water quality as close as possible to existing conditions.

Avoid clearing or filling active or potential nest mounds, hollow-bearing trees, fallen timber, elevated banks and small islands used as refuges.

Avoid breaking connections between nest sites, mangroves, saltmarsh and freshwater wetlands. Fragmentation can reduce feeding resources and nesting opportunities and can increase predator access.

Planning buffer in the guideline: A natural vegetation buffer of at least 30 metres may assist where impacts cannot be avoided.

  • Design the work footprint around retained habitat rather than clearing habitat first and relying on translocation.
  • Keep construction traffic and plant out of intertidal and supralittoral habitat wherever practicable.
  • Prevent stormwater, sediment, contaminants, acid sulfate soil runoff, herbicides, pesticides and oils from entering retained habitat.
  • Do not use translocation as a mitigation or offset for habitat loss, because it does not reduce the impact of the action.

Before habitat disturbance: Approvals and work planning

Check the current EPBC Act status, approved conservation advice, current national recovery plan and any applicable referral guideline before finalising the footprint. The older recovery plan is identified as superseded by the 2023 national recovery plan.

Contact the relevant Queensland or Northern Territory authority and local government about state or territory approvals, protected wildlife requirements, survey requirements and handling permissions.

Plan for the possibility of breeding and nest use throughout the year. The available information indicates that breeding may occur throughout the year, so do not assume that a winter or summer clearing window is safe.

  • Refer the action under the EPBC Act if it may significantly affect an important population, breeding, dispersal between habitat patches or habitat critical to the species' survival.
  • Prepare a fauna management plan that identifies habitat limits, survey results, exclusion zones, stop-work triggers, authorised handlers, incident contacts, release sites and reporting requirements.
  • Stage clearing so that retained habitat, hydrology and movement connections remain available while work proceeds.
  • Schedule high-noise, wetland and intertidal works to avoid active tides and periods when access or animal welfare cannot be managed safely.

Before habitat disturbance: Prepare the site

Complete the pre-clearance habitat and nest search immediately before disturbance, because nest mounds may be reused by successive generations and may be difficult to detect without a targeted search.

Mark exclusion zones around active or potential nest mounds, supralittoral banks, hollow trees, fallen timber, wetland edges and other features identified by the ecologist.

Fence or otherwise protect retained habitat where fencing can be installed without altering tidal flow, trapping animals or damaging mangrove roots.

Brief machinery operators, supervisors and fauna spotter catchers on the species' appearance, nocturnal behaviour, nest features, work limits and stop-work procedures.

  • Place clear no-go markers on both sides of habitat corridors and around nest features before machinery enters the site.
  • Inspect fencing daily for gaps, undercutting, tide damage and trapped wildlife.
  • Keep access tracks, laydown areas, spoil storage and refuelling areas outside retained wetland and supralittoral habitat.
  • Use a qualified person to inspect any proposed spoil heap, bank or fill area because the species may use human-created spoil heaps for nesting.

During habitat disturbance: Daily controls and machinery interface

The fauna spotter catcher should control the interface between machinery and retained habitat. The animal is small, nocturnal and able to shelter in mud mounds, banks, hollow trees and other concealed sites, so visual checks alone are not enough.

Hold a daily pre-start briefing covering the approved footprint, exclusion zones, weather, tide, recent fauna records and the stop-work contact.

Keep the fauna spotter catcher in a position where the operator can see and stop on instruction before the bucket, blade, vehicle or worker enters a habitat exclusion zone.

Clear progressively in small sections, inspect each section, and do not allow machinery to work ahead of the completed fauna inspection.

Maintain sediment, erosion, spill, weed, fire and stormwater controls throughout the shift, particularly beside mangroves, saltmarsh and freshwater wetlands.

  • Stop machinery immediately when the spotter catcher identifies a Water Mouse, nest mound, burrow, hollow, injured animal or unexpected wetland connection.
  • Do not drive over nest mounds, supralittoral banks, crab-rich feeding areas, hollow trees, fallen timber or marked movement corridors.
  • Prevent domestic dogs, cats, foxes, pigs and other uncontrolled animals from entering the work area or retained habitat.
  • Record daily weather, tide, work area, machinery used, inspections, fauna observations and any control failure.

During habitat disturbance: Habitat features and wetland protection

Treat mud mounds, holes in supralittoral banks, nests at tree bases, hollow trunks, elevated islands, spoil heaps and fallen timber as potential refuge or breeding features.

Do not move, collapse, fill, burn or drain a nest feature unless the action is authorised under the fauna management plan and the qualified ecologist has assessed the risk.

Protect mangrove roots, tidal channels, pools, crab holes, pneumatophores and wetland margins because they provide feeding and refuge microhabitats.

Keep clearing debris, sediment, concrete washout, fuels, oils and chemicals out of tidal and freshwater flows.

  • If a hollow-bearing tree must be removed, follow the approved hollow-tree procedure and have the fauna spotter catcher inspect the tree and surrounding ground before, during and after removal.
  • Inspect logs, rocks, spoil heaps and bank faces before they are moved, but do not assume that moving them will safely relocate an animal.
  • Maintain a clear connection from any retained nest or wetland refuge to nearby retained habitat.
  • Stop work if construction changes tidal amplitude, drainage, salinity, sediment movement or freshwater inflow outside the approved design.

During habitat disturbance: Animal encounter, injury and records

Stop work and establish a quiet exclusion zone if a Water Mouse is found. Keep people, vehicles and dogs away and allow the authorised fauna handler to assess the animal.

Only a person authorised under the project approval, fauna management plan and relevant wildlife requirements should capture, handle or relocate the animal.

Use the least handling possible. If immediate relocation is required for welfare, move the animal only to nearby suitable retained habitat identified in the plan, not as a substitute for habitat protection or as an offset.

Take an injured or distressed animal to an appropriately experienced veterinarian or licensed wildlife carer through the nominated project contact.

  • Do not chase an animal into water, a burrow, a hollow or dense mangrove roots.
  • Do not disturb an occupied nest to obtain a capture unless the authorised ecologist determines that this is necessary and lawful.
  • Keep the animal in a secure, quiet container only for the shortest period required by the approved handling procedure.
  • Record the date, time, exact location, habitat, behaviour, photographs, handler, action taken, release location, injury and outcome.
  • Notify the project environmental officer and relevant authority of a capture, injury, death, nest disturbance, unapproved impact or repeated sighting.

After habitat disturbance: Post-clearance checks

Completion of clearing does not end the risk. Check the disturbed area, retained habitat and controls for delayed injury, nest damage, hydrological change, predator access and pollution.

Have the fauna spotter catcher and ecologist inspect the completed work area, retained habitat edges, access tracks, spoil areas, wetland margins and exclusion fencing.

Search for injured or displaced animals, fresh nest damage, collapsed banks, blocked channels, altered flows, sediment deposition, oil or chemical contamination and new predator access.

Reinstate damaged fencing, erosion controls, habitat markers and drainage controls before the next work stage.

  • Complete a final daylight search for nests and signs after each clearing stage.
  • Inspect any retained nest mound, hollow tree, bank, log or wetland refuge that was within the disturbance risk area.
  • Keep plant and spoil out of retained habitat until the environmental officer confirms that the area is stable and controls are working.

After habitat disturbance: Monitoring and reporting

Monitor retained habitat for Water Mouse activity, nest use, prey middens, hydrology, salinity, vegetation condition, weeds and predator activity for the period specified in the approval or fauna management plan.

Use repeat daytime searches and, where required, night-time Elliott trapping to compare activity with the pre-work survey. Apply the same methods and effort where comparison is intended.

Review monitoring results through the project's adaptive management process and change controls if habitat condition or Water Mouse activity declines.

  • Report captures, deaths, injuries, nest damage, habitat loss, hydrological changes and control failures to the relevant authority and wildlife database where required.
  • Provide the final survey, clearing, fauna handling, incident and monitoring records to the project environmental officer and approval holder.
  • Escalate repeated records near the works, loss of nest features, new fragmentation or declining activity as a management trigger.

After habitat disturbance: Ongoing obligations and offsets

Maintain buffers, fencing, drainage controls, weed controls and predator controls for as long as required by the approval, management plan or rehabilitation program.

Do not describe relocation as an offset or use it to justify removal of Water Mouse habitat.

Where an approved action still causes a residual significant impact, apply the conditions of the approval and any lawful offset requirement separately from on-site avoidance and mitigation.

  • Confirm that any offset or conservation measure is approved and consistent with the current recovery plan and conservation advice.
  • Continue protecting retained habitat after construction, including from vehicle access, fire, livestock, recreational disturbance and pollution.
  • Submit required completion and compliance reports within the approval timeframes.

Rehabilitation actions: Restore habitat and hydrology

Rehabilitation should restore the wetland functions that support Water Mouse feeding, refuge, nesting and movement. Protect existing habitat first, because newly planted or constructed features may not provide equivalent habitat for many years.

Reinstate natural tidal and freshwater flows, drainage paths, inundation patterns and salinity as far as practicable after construction.

Replant or allow natural regeneration of locally appropriate mangrove, saltmarsh, saline grassland, sedgeland, heathland and freshwater wetland communities that were disturbed by the project.

Retain or reinstate supralittoral banks, elevated wetland margins and small dry refuges above high tide where they are part of the approved rehabilitation design.

Use local reference sites and pre-disturbance vegetation records to set rehabilitation targets rather than relying only on planted area.

  • Prevent sediment, stormwater, acid sulfate soil runoff and contaminated water from entering the rehabilitation area.
  • Do not reshape or compact wetland soils in a way that blocks crab holes, channels, pools or root microhabitats.
  • Protect regenerated habitat from vehicles, cattle, pigs and other hard-hoofed animals until it is established.
  • Do not use fire in supralittoral or wetland habitat unless it is specifically assessed, authorised and managed under the fire plan.

Rehabilitation actions: Reinstate refuge and prey features

Retain existing hollow trees, fallen timber, driftwood, root structures and natural banks wherever safe and practicable.

Where approved rehabilitation requires replacement refuge, use locally sourced logs, hollow structures or nest boxes only under a design approved by the ecologist. The documents do not establish a standard nest-box size or placement for this species.

Restore conditions that support marine and freshwater invertebrates, including crabs, molluscs and other prey recorded from Water Mouse habitat.

Control weeds, especially Mimosa pigra and exotic pasture grasses in the Northern Territory, and manage invasive plants that alter wetland structure or prey resources.

  • Place replacement features in retained or rehabilitated habitat connected to mangroves, saltmarsh or freshwater wetlands, not in isolated planted areas.
  • Inspect artificial or restored features for occupancy, damage, flooding, predators and weed growth.
  • Use predator and livestock exclusion where cats, foxes, dogs, pigs or cattle threaten restored habitat.
  • Coordinate rehabilitation with landholders and managers where habitat crosses freehold, reserve, marine park or Traditional Owner managed land.

Rehabilitation actions: Monitor rehabilitation success

Monitor vegetation establishment, wetland hydrology, salinity, water quality, prey resources, nest features, weeds and predator activity.

Repeat daytime nest searches and use night-time Elliott trapping where the approval or monitoring design requires evidence of Water Mouse use.

Compare results with the pre-disturbance survey and a suitable retained reference area, using consistent search locations and effort.

Survey comparison effort: For population density work, use at least 400 Size A Elliott trap nights per four to five hectares of potential habitat.

  • Set success measures for functioning tidal and freshwater connections, stable wetland margins, established native vegetation, reduced weeds, controlled predators and continued or returning Water Mouse signs.
  • Treat new nest mounds, fresh mud plastering, middens, captures or repeated sightings as evidence of use and adjust maintenance to avoid disturbance.
  • Investigate failure where hydrology, vegetation or prey conditions do not recover, and implement corrective works through adaptive management.
  • Submit rehabilitation and monitoring results to the approval holder, relevant authority and relevant state wildlife database where required.

Sources