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Balston's Pygmy Perch (Nannatherina balstoni)

Balston's pygmy perch is a small freshwater fish endemic to south-western Western Australia. It lives in shallow, acidic and tannin stained streams, pools, lakes and wetlands, and is vulnerable to altered flows, salinity, sedimentation, eutrophication and introduced fish on development sites.

Conservation status

Commonwealth, EPBC Act 1999: Vulnerable.

Western Australia, Biodiversity Conservation Act 2016: Vulnerable.

Breeding season

The annual pattern below applies to the south-western Western Australian populations described in the source documents. Timing can vary with flooding, flow and local conditions.

Months are January to December. A value of 0 means not typical, 1 means occurs, and 2 means peak.

  • Breeding: Breeding occurs from early winter to late winter and early spring. Flooding stimulates breeding, and spawning is recorded from June to September.
  • Young: Larvae feed predominantly on cladocerans after spawning. The supplied documents do not define the duration of the larval or dependent period, so this row indicates the likely post-spawning period rather than a measured dependence period.
  • Seasonal movement: The documents identify movement barriers and the value of fish passage, but do not provide a defined annual migration window for Balston's pygmy perch. Fish may use connected pools, streams, lakes and wetlands as water levels change.
  • Highest clearing risk: Risk is highest during the June to September breeding and spawning period because adults use inundated riparian vegetation and shallow vegetated margins. Hydrology, sediment and pollution controls are needed year round because the species can occupy permanent and seasonal waterbodies.

Identification

Balston's pygmy perch is a small, elongate fish with a distinctive diamond or cross-hatched pattern along the sides. Identification should be confirmed by an experienced freshwater fish ecologist where it occurs with western pygmy perch.

Adults have a brownish back, a silvery belly, a prominent brown stripe along the side and a series of vertical brown bars. Together these markings form a diamond-shaped or cross-hatched pattern, with tan diamonds over brown or brown diamonds over tan.

The body is more elongate than that of other local pygmy perches. It has a relatively large mouth and a relatively large eye in proportion to the head.

Maximum length: 90 mm

Body pattern: Diamond-shaped or cross-hatched markings along the sides

Colour: Brownish back and silvery belly

Identification: Similar species

The species can occur with western pygmy perch, Edelia vittata, and is usually less abundant where they co-occur. Small pygmy perches can be difficult to distinguish in the field, so experience with the group is required.

Use the more elongate body, large mouth, relatively large eye and diamond-shaped side pattern as supporting characters. Do not rely on colour alone, because the apparent contrast between the diamonds and background can vary.

  • Have a trained fish ecologist confirm records where western pygmy perch or other small pygmy perches are present.
  • Handle captured fish with wet hands, keep them in water while processing and minimise contact because their scales are easily lost.

Identification: Field signs and sex

There are no documented terrestrial field signs such as tracks, scats, nests, calls, sloughs or eyeshine. Detection depends on observing or capturing fish in suitable freshwater habitat.

The supplied sources do not provide external field characters for separating males and females. Sex should not be assigned from a brief visual inspection unless a suitably experienced fish biologist confirms the character.

  • Treat shallow, slow-flowing or still, tannin stained freshwater with sedges or inundated riparian vegetation as potential habitat during site inspections.
  • Use non-destructive visual observation, fine mesh netting, trapping or backpack electrofishing as appropriate to the waterbody and approved survey method.

Distribution: State and regional range

Balston's pygmy perch is endemic to Western Australia. Its current range is concentrated in fragmented coastal drainage systems and wetlands in the south-west, with historical records extending farther north.

The species is known only from Western Australia. The current distribution extends from the Margaret River area to the Goodga River near Albany, generally in waterways within about 30 km of the coast.

It occurs within the South West and South Coast natural resource management regions. The South Western Australia Temperate Forests conservation management zone contains 100 percent of the mapped distribution reported for the species in that source.

State: Western Australia only

Current coastal range: Upper Margaret River to the Goodga River near Albany

Typical distance from coast: Within about 30 km

Natural resource management regions: South West and South Coast

Distribution: Strongholds and subpopulations

The centre of the present distribution is the peat flats of the Doggerup, Gardner and Shannon River watersheds. Other named river systems and wetlands with records include the Margaret, Scott, Donnelly, Deep, Kent and Denmark Rivers, Lake Quitjup, Lake Muir, Broke Inlet and Two Peoples Bay.

The assessment identified 13 primary locations across these river systems and watersheds. Populations are confined to a few smaller streams within the larger river systems and are severely fragmented.

Primary locations: 13

Named central watersheds: Doggerup, Gardner and Shannon

Two Peoples Bay record: Goodga River system and associated aquatic habitats

  • Give particular attention to fresh headwater streams, small tributaries, lakes and wetlands within the listed catchments.
  • Do not assume that a development site is unsuitable because it is outside a known stronghold. Historical records indicate that the former range was broader.

Distribution: Population size and trend

The former range extended from the Moore River north of Perth to Two Peoples Bay. The species is no longer found in the northern half of that range and has disappeared from rivers between Moore River and Margaret River, representing an estimated contraction of about 50 percent.

Most surveyed sites within the remaining range recorded fewer than 10 fish. The population estimate in the listing assessment was approximately 12,000 individuals, but quantitative historical trend data were not available.

Estimated range contraction: About 50 percent

Estimated area of occupancy: About 2,000 km²

Estimated annual population: Approximately 12,000 individuals

Typical record at surveyed sites: Generally fewer than 10 fish per site

Trend evidence: No quantitative historical trend data were available in the listing assessment

Habitat: Waterbodies and water quality

The species occupies low-salinity freshwater in coastal peat flats and associated drainage systems. It is most closely associated with shallow water, dense sedges, inundated riparian vegetation and complex instream cover.

Suitable habitat includes shallow pools, slow-flowing streams, lakes, wetlands, small tributaries and headwaters. Water is commonly acidic, tannin stained and low in salinity.

Some summer records are from pools and creeks that can dry out. These seasonal waterbodies may still provide habitat when water is present and should not be dismissed solely because they are ephemeral.

Water type: Freshwater, often acidic and tannin stained

Flow preference: Slow-flowing or still water

Salinity: Low salinity; the species has only been recorded from fresh water

  • Map all pools, drainage lines, wetlands, lakes and connected low-flow channels that could receive runoff or altered groundwater from the project.
  • Protect low salinity conditions and prevent sediment, nutrients, contaminants and altered inflows from entering occupied or connected habitat.

Habitat: Vegetation and structure

The species is commonly associated with tall sedge thickets, inundated riparian vegetation and complex instream habitat. These features provide cover and are used during the breeding season.

The supplied documents do not identify a particular tree size, vegetation community or elevation limit. The known range is near coastal south-western Western Australia and includes peat-flat catchments.

Key vegetation: Tall sedge thickets and inundated riparian vegetation

Key physical structure: Complex instream habitat and shallow margins

Elevation limit: Not specified in the supplied documents

  • Retain inundated sedges, riparian vegetation, undercut margins, woody structure and other complex instream cover where practicable.
  • Inspect connected wetlands and riparian areas, not just the channel footprint, because the fish uses shallow vegetated margins.

Foraging habitat: Diet

Balston's pygmy perch feeds in shallow vegetated freshwater habitats. Young fish rely mainly on small aquatic crustaceans, while adults take a substantial amount of terrestrial prey.

Larvae feed predominantly on cladocerans. Adult fish mainly eat terrestrial fauna, including arachnids and adult hymenopterans, beetles and flies. Other sources describe terrestrial and aquatic insects as a major part of the diet.

The species is a surface feeder, which increases its exposure to competition and attack from introduced mosquitofish that use a similar niche.

Larval prey: Predominantly cladocerans

Adult prey: Arachnids, adult hymenopterans, beetles, flies and other terrestrial or aquatic insects

Feeding position: Surface feeding

  • Retain overhanging and inundated riparian vegetation that can support terrestrial invertebrates and provide access to the water surface.
  • Avoid activities that remove shallow vegetated margins or reduce the aquatic invertebrate community through sedimentation, eutrophication or contamination.

Foraging habitat: Foraging area

The supplied documents do not provide a measured foraging range or home-range size. For project assessment, treat the occupied pool, stream reach, vegetated margin and connected wetland as feeding habitat, together with upstream areas that influence water quality and flow.

  • Assess direct and downstream effects on the full connected waterbody, not only the area where fish are captured.
  • Prevent turbid or nutrient-rich runoff from entering shallow feeding areas.

Breeding habitat: Breeding biology

Breeding occurs in winter and early spring, when the species is associated with inundated riparian vegetation. Flooding can stimulate breeding, and spawning habitat is vulnerable to changes in flow and water level.

The species generally breeds once in its first year. Many individuals die after their first spawning season, although some survive for more than three years.

Larvae develop in freshwater habitats where small aquatic prey, particularly cladocerans, are available. The supplied documents do not provide a clutch or egg count, gestation period, incubation period or confirmed age at maturity.

Breeding season: Early winter to late winter and early spring

Spawning months: June to September

Breeding trigger: Flooding can stimulate breeding

Age at maturity: Not specified; most individuals spawn in their first year

Clutch or egg number: Not specified in the supplied documents

Incubation or gestation: Not specified in the supplied documents

Lifespan: Usually about one year; some individuals live for more than three years

Breeding habitat: Breeding habitat features

In winter and spring, adults are typically found among inundated riparian vegetation, where they are thought to feed and spawn. Tall sedge thickets and shallow freshwater margins are therefore breeding habitat features.

Maintaining natural inflows, water levels, low salinity and connected shallow habitat is important during the breeding period.

  • Avoid clearing, draining, infilling or channelling inundated sedges and riparian margins from June to September where practicable.
  • Prevent temporary works, crossings and dewatering from interrupting inflows or stranding shallow breeding habitat.
  • If works cannot avoid occupied habitat, obtain advice from the relevant Western Australian fauna and threatened species authorities before disturbing the site.

Sheltering habitat: Cover and refuge

The species shelters within shallow freshwater habitat, particularly dense sedges, inundated riparian vegetation and other complex instream structure. No separate den, burrow, hollow or roost structure is used.

Important refuge features include tall sedge thickets, inundated riparian vegetation, shallow margins and complex instream habitat. These features provide cover for fish and larvae and may reduce exposure to introduced predators.

The species can persist in pools and creeks that dry up during summer, but the supplied documents do not define the minimum pool depth or duration needed for survival.

Shelter type: Tall sedges, inundated riparian vegetation and complex instream habitat

Minimum refuge dimensions: Not specified in the supplied documents

Seasonal refuge: Pools and creeks that may dry up in summer

  • Keep fish habitat wet and connected where possible during construction and operation.
  • Retain aquatic vegetation and instream structure rather than clearing the entire channel margin.
  • Use fish rescue and relocation procedures directed by an experienced aquatic fauna practitioner if dewatering is unavoidable.

Sheltering habitat: Barriers and connectivity

Dams and weirs can restrict fish movement and reduce access to upstream habitat. A vertical slot fish ladder at the Goodga River weir enabled upstream movement of fish species and expanded available habitat, showing that passage can matter in this catchment.

  • Keep temporary barriers, culverts and diversion channels from blocking movement between pools, streams, lakes and wetlands.
  • Assess fish passage at existing and proposed crossings, weirs and water-control structures.

Threats: Clearing and hydrology change

The main threats are loss and degradation of freshwater habitat, salinisation and introduced fish. Clearing and infrastructure works can affect this species through direct habitat removal, altered hydrology and contaminated runoff.

Habitat alteration can result from changed inflows, water regulation and abstraction, groundwater extraction, road maintenance, mineral sand exploration and mining, and agricultural or forestry practices in upper catchments.

These activities can alter water-table levels and flow regimes and increase runoff, salinity, sedimentation or eutrophication. A project can therefore affect the species downstream even where the fish habitat is not directly cleared.

Hydrology-related pressures: Flow regulation, abstraction, groundwater extraction, altered runoff and drying

Water-quality pressures: Salinisation, siltation and eutrophication

Relevant project activities: Road maintenance, mining, urban and rural development, agriculture and forestry

  • Maintain natural inflows and avoid dewatering, drainage interception, excessive groundwater drawdown and rapid changes in water levels.
  • Design road crossings and construction drainage to prevent sediment, nutrients and contaminated water entering occupied or connected habitat.
  • Stage works to avoid disturbance to inundated breeding margins from June to September where practicable.
  • Protect small tributaries, headwaters, lakes and seasonal pools as well as the main channel.

Threats: Fragmentation and barriers

The species has a severely fragmented distribution and is now restricted to small streams, tributaries and lakes that remain fresh and relatively undisturbed. Dams and weirs can prevent movement between suitable reaches.

Habitat loss from urban and rural development is considered a major reason for the disappearance of the species from parts of its former range.

  • Keep connected freshwater habitat and avoid isolating pools or wetlands with roads, bunds, culverts or temporary crossings.
  • Provide fish passage where a project creates or modifies a barrier, using a design suited to the local hydrology and fish community.
  • Survey both upstream and downstream of a proposed crossing or barrier because presence may vary between connected reaches.

Threats: Introduced fish

Introduced eastern mosquitofish, Gambusia holbrooki, are widespread in Western Australia and can compete with or attack small endemic fish. Redfin perch, rainbow trout and brown trout may also prey on or compete with Balston's pygmy perch.

Other native fish moved from eastern Australia, including golden perch and Macquarie perch, have also been introduced into surrounding catchments and may threaten small endemic fish.

Key introduced species: Eastern mosquitofish, redfin perch, rainbow trout and brown trout

Potential impacts: Predation, aggression and competition

  • Do not release, move or introduce fish or water containing fish between catchments.
  • Prevent construction activities from connecting previously isolated waterbodies unless the ecological consequences have been assessed.
  • Report suspected introduced fish in occupied catchments to the relevant Western Australian authority.

Threats: Fire, roads and disease

The supplied species sources do not identify disease as a confirmed major threat, and they do not provide a species-specific fire threshold. Fire can still affect aquatic habitat indirectly through loss of riparian cover, increased runoff, erosion and sedimentation.

Road construction and maintenance are identified sources of risk because they can alter drainage, increase sediment inputs and create barriers to movement.

  • Manage post-fire and construction runoff so that ash, sediment and nutrients do not enter occupied streams, pools or wetlands.
  • Keep road drains, crossings and temporary access tracks from concentrating dirty water into fish habitat.
  • Include disease prevention in aquatic fauna hygiene procedures, including cleaning and drying equipment between catchments.

Survey methodology: 1. Define habitat and survey area

Balston’s Pygmy Perch is a small, short-lived freshwater fish of shallow, slow-flowing or still waters. Survey design must cover low-salinity, acidic and tannin-stained pools, streams, lakes, wetlands, tall sedge thickets and inundated riparian vegetation within the species’ known range in south-western Western Australia.

Map all rivers, streams, pools, lakes, wetlands, drainage lines and inundated riparian vegetation that could be affected directly or indirectly by the project.

Include downstream and upstream areas where changes to flow, water quality, salinity, sediment or groundwater could affect habitat.

Give particular attention to shallow freshwater habitats within 30 kilometres of the south-western Western Australian coast between Margaret River and Albany, including the Goodga River area.

Maximum recorded length: 90 mm

Known distribution: Near-coastal streams, lakes and wetlands between the upper Margaret River and the Goodga River near Albany

Typical habitat: Shallow, low-salinity, acidic and tannin-stained water with complex instream habitat

  • Record water depth, flow condition, salinity or conductivity where practicable, water colour, acidity or pH where practicable, aquatic vegetation, tall sedge thickets, riparian vegetation and instream cover.
  • Treat historically occupied sites as potential habitat even where fish are not detected, because the species’ range has contracted and populations are fragmented.

Survey methodology: 2. Select suitable capture methods

Use a combination of methods suited to water depth, flow, access, vegetation and substrate, because the survey guideline identifies backpack electrofishing and trapping as effective methods for pygmy perches.

Use backpack electrofishing in wadeable still water, shallow flowing streams and riffles, operated under the Australian Code of Practice and in a way that minimises fish injury.

Use fine-mesh seine nets with electrofishing where suitable, securing the seine downstream as a cod-end, or use a person with a dip net to collect missed fish.

Use small one-person nets, including Japanese scoop nets and dip nets, where appropriate, while avoiding unnecessary disturbance to dense vegetation and the stream bed.

  • Keep captured fish in a container of water for the shortest practical time and return them promptly to suitable habitat after identification and processing.
  • Use wet hands and minimal contact because small south-eastern Australian freshwater fishes are sensitive, easily stressed and prone to scale loss.
  • Do not use boat-based electrofishing as the default method, because it is generally unsuitable for most members of this fish group.

Survey methodology: 3. Time surveys to avoid breeding disturbance

Do not plan routine survey capture during the breeding period where this can be avoided.

Balston’s Pygmy Perch breeds in winter, with spawning from June through September, and flooding stimulates breeding in the middle of winter.

Schedule surveys outside June to September where the project program allows, while recognising that a suitable survey season does not remove the need to protect occupied habitat.

Breeding period to avoid: June to September

Breeding cue noted in the guideline: Winter flooding

  • Record recent rainfall, flow conditions and water levels because flooding can stimulate breeding and water conditions affect detectability.
  • If work or survey during the breeding period cannot be avoided, document the reason, obtain required approvals and use the least disturbing method available.

Survey methodology: 4. Identify fish correctly and document detection

Have an experienced freshwater fish ecologist or trained ichthyologist confirm identifications where Balston’s Pygmy Perch could be confused with Western Pygmy Perch.

Look for the species’ diamond or cross-hatched side pattern, brownish back, silvery belly, relatively elongate body, large mouth and relatively large eye.

Record survey locations, dates, times, methods, effort, habitat conditions, water quality observations, fish numbers, life stages, photographs and any handling or mortality.

  • Do not treat a non-detection as proof of absence where habitat is suitable, survey conditions are poor, historical records exist or survey effort was limited.
  • Record co-occurring introduced fish, including Eastern Mosquitofish, Redfin Perch, Rainbow Trout and Brown Trout, because these species may prey on, attack or compete with Balston’s Pygmy Perch.

Survey methodology: Minimum effort and reporting

  • Use a documented combination of backpack electrofishing, trapping, fine-mesh seining and dip or scoop netting that samples each suitable habitat type and explains why any method was not used.
  • Do not claim a site is free of Balston’s Pygmy Perch unless the report describes the area searched, habitat sampled, methods, dates, seasonal conditions, effort and detection limitations.
  • Avoid June to September for routine survey work where practicable and clearly justify any survey undertaken during that period.
  • Submit confirmed records, including reliable non-detections where required by the data custodian, to the relevant Western Australian wildlife or biodiversity database and provide records to the project approval authority.
  • Retain field sheets, photographs, electrofishing or trapping records, specimen or tissue records where authorised, GPS locations and chain-of-custody information.
  • Report any confirmed occurrence promptly to the project ecologist and environmental officer so the work method, exclusion area and approvals can be reviewed.

Before habitat disturbance: Avoid and minimise habitat loss

Plan the project around the species’ dependence on fresh, low-salinity water and intact wetland and riparian structure. The main risks are altered inflows, drying, salinisation, siltation, eutrophication, pollution, physical barriers and introduced fish.

Avoid clearing or excavating shallow pools, streams, lakes, wetlands, tall sedge thickets and inundated riparian vegetation that provide habitat.

Retain natural flow paths, groundwater connections, riparian cover, instream vegetation and complex instream habitat.

Keep construction compounds, stockpiles, access tracks, refuelling areas and spoil away from waterways and wetlands.

Design the work to prevent changes in inflow, water-table levels, runoff, sediment delivery, pollution and salinity.

  • Use the smallest practicable disturbance footprint and retain connected habitat between occupied or potentially occupied water bodies.
  • Do not drain, divert, dam, culvert or isolate habitat unless the action has been assessed, approved and designed to maintain fish passage and suitable flow.
  • Avoid new barriers at dams, weirs, crossings and temporary water-control structures; investigate fish passage where a barrier cannot be avoided.

Before habitat disturbance: Check approvals and plan the works

Confirm whether the action requires referral or approval under the Environment Protection and Biodiversity Conservation Act 1999 because Balston’s Pygmy Perch is nationally listed as vulnerable.

Confirm Western Australian Biodiversity Conservation Act approvals, permits, licences and fauna handling requirements before disturbing habitat or capturing fish.

Prepare a species-specific fauna management plan covering survey results, exclusion areas, water-quality controls, fish handling, relocation, stop-work triggers, incident response and reporting.

Stage works so that habitat is retained until the relevant construction area has been surveyed, cleared under supervision and protected from machinery and runoff.

Commonwealth status: Vulnerable under the EPBC Act

Western Australian status: Vulnerable under the Biodiversity Conservation Act 2016, as reported by the state department

  • Consult the relevant state wildlife authority before works in occupied or potential habitat, particularly where fish capture, relocation, dewatering, barriers or changes to flow are proposed.
  • Include downstream effects and indirect effects from altered flow, sediment, salinity, nutrients, groundwater extraction and drying in the approvals assessment.
  • Nominate an ecologist, fauna spotter catcher or other authorised person responsible for daily environmental decisions.

Before habitat disturbance: Prepare and mark the site

Complete a pre-clearance habitat and fish survey before access, dewatering, vegetation removal, earthworks or installation of temporary crossings.

Mark all retained waterways, wetlands, riparian vegetation, sedge thickets, pools, fish passage routes and no-go areas on plans and on the ground.

Install exclusion fencing or other visible barriers where they can protect retained wetland and riparian habitat from machinery, vehicles, sediment and accidental entry.

Brief all workers on the species’ appearance, habitat, legal status, exclusion areas, reporting requirements and the stop-work procedure.

  • Inspect exclusion fencing, sediment controls, drains, bunds and water-control structures before work starts and after rainfall.
  • Do not place fencing, silt controls or access tracks across fish habitat in a way that blocks fish movement or concentrates dirty water into retained habitat.
  • Mark any introduced fish control area separately and prevent translocation of fish, water, mud or equipment between catchments without suitable decontamination.

During habitat disturbance: Daily controls and machine coordination

Keep work away from occupied or potential aquatic habitat and maintain clean, connected water. A fauna spotter catcher must work as part of the machine-control team, not as a substitute for project planning or approvals.

Hold a daily pre-start briefing with the supervisor, machinery operators, environmental officer and fauna spotter catcher before work near waterways or wetlands.

Inspect exclusion zones, sediment and erosion controls, flow controls, dewatering systems and access points each day and after rainfall.

Keep machinery, fuels, concrete washout, chemicals, spoil and waste outside retained habitat and prevent dirty water from entering pools, streams, lakes or wetlands.

Use the spotter catcher to direct machinery around marked habitat and to stop work when an animal, occupied habitat or an unplanned water-quality risk is identified.

  • Keep water movement, turbidity, sediment, nutrients, contaminants and salinity changes to the minimum practicable level.
  • Do not allow pumping, trenching, crossings or temporary bunds to strand fish, isolate habitat or change flow without an approved method and authorised fauna supervision.
  • Clean and inspect equipment before moving between waterways or catchments to reduce the risk of moving introduced fish, eggs, pathogens, sediment or contaminated water.

During habitat disturbance: Fish capture, handling and relocation

If fish must be removed from a work area, use only an authorised person and the approved capture and relocation method.

Use methods suitable for the site, such as backpack electrofishing, fine-mesh seines, traps or dip nets, and keep fish in water for the shortest practical time.

Handle fish with wet hands and minimal contact, and return them promptly to nearby retained habitat with suitable fresh, low-salinity conditions unless the approval specifies another location.

Do not move fish between catchments or introduce native fish from elsewhere in Australia.

  • Confirm the identification of any small pygmy perch before relocation because Balston’s Pygmy Perch can be confused with Western Pygmy Perch.
  • Record the capture location, date, method, number, condition, identification, relocation location, person responsible and any mortality.
  • Send injured fish to an appropriately qualified aquatic veterinarian, wildlife carer or other approved facility where such treatment is available and authorised.

During habitat disturbance: Habitat features and stop-work triggers

Treat shallow pools, slow-flowing channels, sedge thickets, inundated riparian vegetation, submerged vegetation, logs and other instream cover as potential fish habitat unless a suitably qualified ecologist confirms otherwise.

Protect retained waterways from silt, concrete, hydrocarbons, herbicides, fertilisers, sewage, excess nutrients and altered drainage.

Stop work immediately if Balston’s Pygmy Perch is found, if fish are stranded, if a protected exclusion area is breached, if water becomes visibly polluted or turbid, or if flow is changed beyond the approved method.

Stop and notify the environmental officer if a dam, weir, culvert, crossing or temporary structure blocks fish passage or causes fish to congregate, strand or become exposed.

  • Make the area safe, keep machinery stationary where practicable and prevent further habitat damage before the spotter catcher or ecologist assesses the situation.
  • Do not chase, net or handle the fish unless the person is authorised and the approved fauna management method requires it.
  • Escalate any injury, mortality, unauthorised clearing, pollution event, fish translocation or barrier failure under the project incident procedure and approval conditions.

After habitat disturbance: Inspect and verify the work area

Post-work checks must confirm that retained habitat remains connected, fresh and structurally suitable. They must also test whether controls prevented indirect impacts such as sedimentation, altered flow and introduced fish movement.

Complete a post-clearance inspection of all disturbed and retained waterways, wetlands, pools, riparian vegetation and access points.

Check for stranded or injured fish, dead fish, blocked channels, altered flow, erosion, sediment deposition, turbidity, pollution, dewatering impacts and damage to sedge or riparian habitat.

Remove temporary barriers, spoil, sediment, waste and structures that are no longer required, unless an approved structure is needed to maintain habitat or fish passage.

Repair exclusion fencing, erosion controls, drainage controls and waterway crossings until the site is stable and no longer presents a risk.

  • Repeat fish surveys where the approval, fauna management plan or impact assessment requires verification of occupancy, survival or recolonisation.
  • Use the same or comparable survey methods and habitat observations where possible so post-work results can be compared with baseline data.
  • Retain photographs, GPS points, water-quality observations, capture records, incident reports and rehabilitation inspections.

After habitat disturbance: Monitor and report outcomes

Monitor water quality, water levels, flow, salinity, sediment, aquatic vegetation, riparian cover and fish passage at a frequency set by the approval and risk assessment.

Monitor known or potential Balston’s Pygmy Perch habitat through relevant wet and dry conditions where project impacts could persist beyond construction.

Report confirmed detections, mortalities, injuries, pollution incidents, failed controls, unauthorised impacts and corrective actions to the approval authority and relevant state wildlife database.

Review monitoring results with the project ecologist and change controls if habitat condition, water quality, flow or fish records show an adverse effect.

  • Include any required offset assessment or offset action where residual impacts remain after avoidance and mitigation.
  • Do not treat an offset as permission to damage retained habitat or as a substitute for preventing salinity, drying, sedimentation, pollution or habitat fragmentation.
  • Keep monitoring and reporting records in the project environmental file and provide them to regulators when required.

Rehabilitation actions: Restore aquatic and riparian habitat

Rehabilitation should recreate the freshwater conditions and habitat structure used by Balston’s Pygmy Perch. Focus on flow, water quality, sedge and riparian cover, complex instream habitat and connection between suitable water bodies.

Reinstate natural drainage, shallow pools, slow-flowing channels and wetland inundation patterns where construction has altered them.

Replant or allow recovery of locally appropriate native sedges and riparian vegetation, with priority given to tall sedge thickets and inundated vegetation associated with the species.

Use local native wetland and riparian species selected for the site rather than introducing non-local fish or aquatic organisms.

Stabilise banks and exposed soil with methods that reduce erosion and sediment entry without straightening or simplifying the channel.

  • Retain or reinstate complex instream habitat, including suitable submerged and emergent vegetation and naturally occurring woody cover where it does not create a flood or infrastructure hazard.
  • Do not add fertiliser, nutrient-rich soil or contaminated fill that could increase eutrophication or reduce water quality.
  • Design wetland rehabilitation to retain fresh, low-salinity, acidic or tannin-stained conditions where these occur naturally at the site.

Rehabilitation actions: Restore connectivity and control threats

Remove temporary barriers and design permanent crossings, weirs or water-control structures to maintain fish passage where required by the site assessment and approvals.

Prevent new introductions or translocations of exotic fish and native fish from other parts of Australia.

Develop or support control of Eastern Mosquitofish, Redfin Perch, Rainbow Trout and Brown Trout where they threaten the rehabilitated habitat and control is authorised.

Control weeds and manage sediment, runoff, nutrients, salinity and water extraction so rehabilitated habitat remains suitable over time.

  • Coordinate rehabilitation across connected upstream and downstream habitat rather than treating an isolated work footprint as a complete recovery unit.
  • Consider fire and changing climate in the rehabilitation plan, particularly where they may affect headwater streams, wetlands, riparian vegetation, water levels or water quality.
  • Use formal conservation agreements, covenants or reserve tenure where appropriate to protect restored habitat.

Rehabilitation actions: Set measurable success criteria

Set project-specific success criteria for survival and cover of native sedges and riparian plants, stable banks, functioning flow paths, maintained fish passage, acceptable sediment levels and water quality consistent with reference habitat.

Inspect rehabilitation after rainfall and through contrasting flow conditions to confirm that pools and channels do not dry or scour in an unintended way.

Undertake follow-up fish surveys using authorised, low-impact methods and avoid routine capture during June to September where practicable.

Continue monitoring until the site meets the approved criteria and any residual risks to Balston’s Pygmy Perch have been addressed.

  • Compare post-rehabilitation habitat observations and fish records with baseline and reference sites, and explain any difference in detectability or seasonal conditions.
  • Trigger corrective action if salinity, turbidity, sediment, nutrient enrichment, drying, barriers, introduced fish or vegetation failure develop.
  • Report rehabilitation progress, monitoring results, corrective actions and any confirmed fish records to the relevant approval authority and state biodiversity database.

Sources