Little Pygmy Perch (Nannoperca pygmaea)

Conservation status

Commonwealth, EPBC Act 1999: Endangered.

Western Australia, Biodiversity Conservation Act 2016: Endangered.

Breeding season

The typical annual pattern is based on south-western Western Australian populations. Timing varies with rainfall and river discharge, and fish may remain in permanent refuges when channels stop flowing.

Month values are January to December: 0, not typical; 1, occurs; 2, peak or highest expected use. Timing can shift with rainfall and discharge.

• Dry-season refuge use: During summer baseflow, fish contract into permanent refuge pools. The documents describe hot, dry summers and refuge use when the main channel is dry.
• Upstream movement: The species moves upstream in winter from refuge pools into flowing tributaries or main-channel breeding habitat. The strongest documented movement is associated with winter flow.
• Breeding and spawning: Breeding commenced in July and finished by September in the Mitchell River. The species is a batch spawner and may spawn on multiple occasions.
• Larvae and juveniles: Larval and juvenile timing is not given as a separate measure in the documents. This row reflects the breeding period and the documented importance of winter and spring flow for recruitment.
• Return to refuge pools: Fish return to refuge pools when seasonal flow ceases. In the Hay and Mitchell system, the species was absent from the Mitchell River during non-flow periods and moved back into Hay River pools.
• Highest clearing risk: Clearing or disturbance is most likely to harm the species during summer when fish are concentrated in a small number of refuge pools, and during July to September when fish are moving and spawning. The documents do not provide a formal monthly risk assessment.

Identification

The Little Pygmy Perch is a very small native percichthyid. It is most likely to be encountered in permanent pools during dry periods or in flowing tributaries during winter and spring.

Adults grow to a maximum of 65 mm total length. The supplied studies do not provide a reliable adult weight, detailed colour description or a set of diagnostic field marks for use during construction surveys.

Length frequency data indicate that fish may reach about 30 to 40 mm total length by the end of their first year. Individuals may therefore be very small during aquatic fauna surveys and should be retained for examination where identification is uncertain.

Identification: Similar species

The species is morphologically similar to the sympatric Western Pygmy Perch. Misidentification is a known survey issue, and additional populations may have been overlooked for this reason.

The Little Pygmy Perch also occurs with Balston's Pygmy Perch and other small native fishes. Field identification should be confirmed by an experienced freshwater fish ecologist or taxonomist when animals are captured during works.

• Do not rely on size alone to separate Little Pygmy Perch from Western Pygmy Perch.
• Photograph uncertain specimens and record the pool, channel position, water condition and capture method.
• Use the relevant permit and animal welfare procedures for any capture, handling or release.

Identification: Field signs and survey context

The species leaves no documented terrestrial signs such as tracks, scats, nests, burrows or hollows. Detection is by direct observation, netting or other aquatic survey methods.

Presence changes markedly with flow. In the Hay and Mitchell system, fish moved from Hay River refuge pools into the Mitchell River during the flow period and were absent from the Mitchell River during non-flow periods.

• Treat permanent pools as potential habitat even when the main channel is dry.
• Do not assume that a negative result from a dry main channel indicates local absence.
• Arrange specialist fish identification where small pygmy perches are captured or observed.

Distribution: National range

The Little Pygmy Perch is endemic to south-west Western Australia. Its known distribution is fragmented across several catchments and includes an isolated lake population.

The species is known only from Western Australia. It occurs within the south-western Australian freshwater province, a region with a Mediterranean climate and predominantly winter rainfall.

Known systems include the Hay and Mitchell rivers near Denmark, the Denmark River, the Kent River and Lake Smith. The supplied documents do not assign the species to a formal IBRA bioregion.

Distribution: Known strongholds and subpopulations

The Hay and Mitchell population occupies about 3 km of river and contracts to two major refuge pools in the Hay River during baseflow. The population in this system was small and considered at higher risk than the other known populations.

The species is known from about 30 km of the Denmark River, about 50 km of the Kent River and Lake Smith, which lies more than 200 km from the nearest known population. In the Denmark catchment, four refuge pools were known in Little Pygmy Creek, including two artificial waterpoints.

• Hay and Mitchell rivers: about 3 km of occupied river and two major Hay River refuge pools during baseflow.
• Denmark River: about 30 km of known distribution, including Little Pygmy Creek.
• Kent River: about 50 km of known distribution, with at least two pools supporting high abundance.
• Lake Smith: an isolated population using the permanent lake as a major refuge.

Distribution: Population extent and trend

Three additional populations were discovered during the study, increasing the known range but also showing that populations are fragmented. The species has a small area of occupancy and extreme seasonal changes in range and abundance.

The supplied documents do not provide a current total population estimate or a reliable estimate of long-term population trend. In one Hay River refuge pool, mark and recapture work estimated about 90 Little Pygmy Perch, compared with about 8,117 Western Pygmy Perch in the same pool.

Extent of occurrence: 3,420 km2

Area of occupancy: 10 km2, calculated using 1 km2 grid cells

Hay River refuge estimate: About 90 fish in one surveyed pool

Known locations used for assessment: Four locations were identified in the assessment

Habitat: Overall habitat

The species depends on freshwater river and lake habitats that retain water through the dry period. Habitat use changes between summer refuge conditions and winter flow conditions.

Little Pygmy Perch inhabits permanent refuge pools in the main stem of an ephemeral catchment. In the study area, some main-channel pools were slightly salinised but still used during flow and baseflow periods.

The species also occurs in permanent lake habitat and in seasonally flowing tributaries. In the Denmark catchment, it used the main river and a tributary known as Little Pygmy Creek.

• Permanent river pools that retain water during summer baseflow.
• Main-channel pools in ephemeral or seasonally flowing rivers.
• Seasonally flowing tributaries used during winter movement and spawning.
• Permanent lake habitat, including Lake Smith.

Habitat: Structural and water requirements

The documented habitat feature of greatest importance is persistent water through the dry period. Groundwater supports permanent pools in many south-western rivers, and falling groundwater levels can remove this refuge habitat.

Freshwater conditions are important. In the main study catchment, the species occupied pools where summer salinity remained below 6 parts per thousand. Its full salinity tolerance has not been determined.

• Protect permanent pools, their inflows and groundwater connections from drainage, filling, sedimentation and contamination.
• Retain riparian vegetation along refuge pools, tributaries and spawning reaches.
• Maintain flow paths between summer refuges and winter breeding habitat.
• Prevent works that increase salinity or reduce freshwater inflow to occupied pools.

Habitat: Climate and elevation

The species occurs in a south-western Australian Mediterranean climate, with hot, dry summers and most rainfall in winter. The supplied documents do not provide an elevation range.

Known habitat is strongly affected by seasonal flow. Reduced rainfall, reduced surface discharge and lower groundwater levels are expected to reduce refuge availability and breeding movement.

Foraging habitat: Survey and project guidance

The supplied documents do not report the diet, prey types, feeding method or foraging range of the Little Pygmy Perch.

As a small freshwater fish, individuals may forage within occupied pools, river margins and tributary habitats, but the source documents do not provide species-specific evidence for preferred feeding locations.

For project planning, treat the full wetted area of an occupied refuge pool, connected shallow margins and the flow path to known tributaries as potential habitat until a freshwater fish ecologist has assessed the site.

• Prevent increased turbidity, sediment deposition, chemical spills and rapid dewatering in occupied pools and connecting channels.
• Retain aquatic and riparian structure where it occurs, because the studies identify habitat quality and water quality as conservation concerns even though they do not specify prey or feeding structures.
• Do not infer absence from a dry channel, because fish can remain in isolated refuge pools and move when flow returns.

Breeding habitat: Breeding biology

Breeding is linked to winter flow and upstream movement from dry-season refuge pools into tributary or main-channel habitat. Documented spawning habitat includes the lower Mitchell River and Little Pygmy Creek in the Denmark catchment.

Breeding season: Mainly July to September. Breeding commenced in July and finished by September in the Mitchell River.

Spawning strategy: Batch spawning, with individuals likely spawning on multiple occasions during the breeding period.

Clutch or litter size: Not reported in the supplied documents.

Gestation or incubation: Not reported in the supplied documents.

Age at maturity: Not reported in the supplied documents.

Lifespan: Maximum life expectancy appears to be about four years.

Recruitment: Recruitment was higher in years with greater discharge, based on comparisons between 2013 and 2014.

Breeding habitat: Spawning and nursery habitat

In the Hay and Mitchell system, fish moved upstream in winter from two Hay River refuge pools into the Mitchell River. The lower 3 km of the Mitchell River was identified as a key spawning area.

In the Denmark catchment, Little Pygmy Perch moved upstream into Little Pygmy Creek. This tributary was identified as a key breeding area, while the main Denmark River near the confluence was dry during part of the baseflow period.

The precise breeding area in the Kent River remains unknown, although the likely spawning region was narrowed to a remote part of the mid-catchment.

• Protect the lower 3 km of the Mitchell River from clearing, disturbance, sediment input and flow alteration during winter and spring.
• Protect Little Pygmy Creek and its connection with the Denmark River.
• Maintain upstream and downstream passage between refuge pools and spawning habitat.
• Treat remote mid-catchment tributaries and flowing reaches in the Kent River as potential breeding habitat until surveyed.

Sheltering habitat: River refuges

During baseflow, the Little Pygmy Perch contracts into permanent refuge pools and other habitats that retain water through summer. These pools are the main dry-season sheltering habitat documented for the species.

In the Hay and Mitchell system, the species was restricted to two major refuge pools in the Hay River during baseflow. In the Denmark catchment, it used four refuge pools in Little Pygmy Creek, including two artificial waterpoints.

In the Kent River, the species used middle-reach main-channel pools. At least two pools supported high abundance, and other similar pools are likely to be used. Lake Smith is a permanent refuge for its isolated population.

• Protect all permanent pools within and near known occupied river reaches.
• Retain pool volume, bed structure, shade and riparian cover during construction and access works.
• Avoid pumping from, draining or diverting water from refuge pools.
• Assess artificial waterpoints before modification, infilling or decommissioning because two such sites supported fish in the Denmark catchment.

Sheltering habitat: Refuge dimensions and use

The supplied documents do not provide standard refuge-pool dimensions, depth thresholds or a defined home range. Refuge use is described by pool location and persistence rather than by a measured shelter size.

The species returned to Hay River refuge pools when flow ceased in the Mitchell River. This movement pattern means that habitat connected by seasonal flow should be assessed as one functional system.

• Survey both flowing channels and isolated pools when assessing an impact footprint.
• Include upstream and downstream access routes in the habitat assessment, not only the pool containing fish.
• Maintain groundwater and surface-water inputs that keep refuge pools wet through the dry season.

Threats: Clearing and construction

The main risks are loss of permanent refuge water, reduced seasonal flow, increasing salinity and introduced species. A small, fragmented distribution increases the consequence of disturbance at individual pools or breeding reaches.

Clearing riparian vegetation, disturbing stream beds or altering drainage can affect refuge pools, tributary connections and spawning habitat. The species depends on movement between dry-season refuges and winter breeding areas.

Construction should be planned around occupied pools, the lower 3 km of the Mitchell River, Little Pygmy Creek and other connected tributaries. The source documents do not provide a species-specific clearing buffer.

• Avoid clearing riparian vegetation beside known refuge pools and breeding reaches.
• Keep plant, spoil, sediment and concrete washout away from occupied water.
• Prevent temporary access tracks, crossings and drains from severing seasonal fish passage.
• Use a qualified freshwater fish ecologist to assess dewatering, channel disturbance and relocation requirements before works start.

Threats: Hydrology and salinity

Reduced rainfall, water abstraction and falling groundwater levels can dry critical baseflow refuges, reduce spawning migration and lower recruitment. Higher discharge in 2013 was associated with greater movement and relative abundance than in the drier 2014 sampling period.

Secondary salinisation is a major risk in the Hay and Kent rivers. The study identified summer salinities below 6 parts per thousand in occupied permanent refuge pools, but the species' physiological salinity tolerance has not been determined.

• Avoid groundwater drawdown and surface-water extraction that could reduce pool persistence.
• Maintain natural seasonal flow and the connection between refuge and spawning habitat.
• Prevent saline drainage, concentration of salts and changes to freshwater inflow.
• Monitor conductivity, water level, discharge and pool persistence before, during and after works where habitat is occupied or connected.

Threats: Fragmentation, predators and disease

The species has a severely fragmented range, a small area of occupancy and only four assessment locations. A local loss at one refuge pool or breeding reach may therefore have a disproportionate effect.

Eastern Gambusia occurs with Little Pygmy Perch during baseflow in the Hay River, although the two species were not sympatric in the known Mitchell River breeding habitat. The supplied documents identify introduced species as a potentially catastrophic risk. They do not report a specific disease affecting this species.

• Prevent the movement of Eastern Gambusia and other non-native aquatic species between waterbodies through nets, pumps, boats, vehicles and water tanks.
• Use clean equipment between catchments and follow approved aquatic hygiene procedures.
• Do not release fish, water or aquatic material between sites.
• Treat isolated pools and small tributaries as high-consequence habitat when assessing fragmentation or access works.

Threats: Fire and roads

The supplied documents do not identify fire as a direct species-specific threat, but they record artificial firefighting waterpoints as potential refuge habitat. Fire management, water extraction and road access can therefore affect occupied pools and seasonal flows.

Road crossings and construction access can increase sediment delivery, interrupt fish passage or provide access for water extraction. The supplied documents do not provide a species-specific road mortality rate.

• Check firefighting waterpoints, roadside pools and road crossings for Little Pygmy Perch before modification or water extraction.
• Keep sediment and runoff out of pools and tributaries during road and infrastructure works.
• Maintain fish passage at temporary and permanent crossings.
• Do not use occupied pools as construction or firefighting water sources without ecological assessment and approval.

Survey methodology: 1. Desktop assessment and habitat mapping

Little Pygmy Perch is a small freshwater fish of permanent refuge pools, ephemeral rivers and seasonally flowing tributaries in south-western Western Australia. Surveys must cover both dry-period refuge habitat and winter breeding movements, because fish may be absent from normally occupied river reaches when they stop flowing.

Map permanent and semi-permanent pools, river channels, groundwater-fed reaches, seasonally flowing tributaries and wetlands before fieldwork begins.

Give particular attention to refuge pools that retain water during summer, lower-flow tributaries used for breeding, and connections between refuge pools and spawning reaches.

Include a search area that extends beyond the disturbance footprint because known populations are fragmented and may occur in isolated pools or tributaries.

Known extent of occurrence: 3,420 km2

Known area of occupancy: 10 km2

Known summer refuge in the Hay and Mitchell system: Two major refuge pools

• Review aerial imagery, drainage mapping, hydrology, salinity data, previous records and proposed construction impacts before selecting survey sites.
• Inspect the Hay, Mitchell, Denmark and Kent river types as relevant habitat analogues, noting that the species has been recorded over approximately 3 kilometres in the Hay and Mitchell system, 30 kilometres in the Denmark River, 50 kilometres in the Kent River and at Lake Smith.
• Record water permanence, flow, conductivity or salinity, temperature, depth, aquatic cover, riparian cover and barriers at each site.

Survey methodology: 2. Baseflow refuge surveys

Survey during the dry period when fish are concentrated in permanent refuge pools and the surrounding river channel is dry or has ceased flowing.

Use aerial reconnaissance followed by ground truthing to locate all pools that retain water within and downstream of the project area.

Treat artificial water points as potential habitat where they provide permanent water, because four Denmark catchment refuge pools included two artificial water points.

Maximum recorded length: 65 mm total length

Estimated maximum life expectancy: Four years

Hay and Mitchell refuge estimate: Approximately 90 fish in one surveyed pool

• Inspect every accessible permanent pool within the disturbance area and connected upstream and downstream reaches.
• Use non-destructive fish sampling methods suitable for the site and approved under the relevant state authority permit.
• Identify Little Pygmy Perch carefully because it is morphologically similar to Western Pygmy Perch and may be misidentified during routine fish surveys.
• Record abundance, size classes, water quality, habitat condition and the presence of introduced fish at each pool.

Survey methodology: 3. Fyke-net surveys during flow

Use directional fyke nets to sample movement between refuge pools and tributaries during winter and spring flow. The project study used two directional fyke nets at each of six sites on 14 occasions.

Position nets to intercept both upstream and downstream movement, with locations selected to sample the main channel, tributary entrances and likely breeding reaches.

Check nets at intervals that meet the relevant animal ethics and permit conditions, minimise holding time, and release fish at the capture location unless an approved study requires otherwise.

Breeding period in the Mitchell River: July to September

Breeding peak recorded: August in 2013 and July in 2014

Study fyke effort: Two directional fyke nets at six sites on 14 occasions

• Target the winter to spring breeding period, when Little Pygmy Perch moves upstream from refuge pools to spawn.
• In the Mitchell River, focus on the lower 3 kilometres identified as spawning habitat and on connections from Hay River refuge pools.
• In the Denmark catchment, include Little Pygmy Creek and connected main-channel pools where access and approvals allow.
• Record effort as net type, number of nets, net hours, site location, date, flow, water quality and all fish captured.

Survey methodology: 4. Larval, movement and recruitment surveys

Use larval light traps in likely spawning and nursery habitat where the method is approved and safe. The source study used larval light trapping to identify breeding habitat and associated flow, shade, depth and substrate.

Use mark and recapture only under an approved research design and animal ethics approval. Visual Implant Elastomer tagging was used in the source study to confirm movement from Hay refuge pools into the Mitchell River.

Repeat sampling across contrasting flow years where practicable, because higher discharge was associated with greater movement and recruitment indicators.

Higher-flow comparison in the Mitchell River: August to October discharge was approximately 2.5 times greater in 2013 than in 2014

Breeding strategy: Batch spawning, likely on multiple occasions during the breeding period

Movement type: Potamodromous, within freshwater for breeding

• Sample seasonally inundated tributary margins, flooded vegetation and shallow nursery areas connected to the main breeding reach.
• Measure discharge or flow condition at each visit and relate detections to pool permanence and connectivity.
• Use a fish specialist experienced with small percichthyids to confirm identifications and retain voucher photographs or other approved evidence.
• Do not infer absence from a single failed survey, particularly during non-flow periods when the species may have contracted to refuge pools.

Survey methodology: Minimum effort and reporting

• Use the documented effort of two directional fyke nets at six sites on 14 occasions as a reference point for a targeted assessment, then justify any reduction or increase against habitat extent, access, flow and project risk.
• Survey both summer refuge conditions and winter to spring movement conditions where the project could affect permanent pools, tributaries or flow connectivity.
• Record coordinates, dates, weather, flow, water quality, salinity or conductivity, equipment effort, catch, identification evidence, injuries, releases and habitat condition.
• Submit confirmed records and negative survey results to the relevant Western Australian wildlife or biodiversity database and provide records required by the project approval.
• Report any likely impact to a known population, refuge pool or spawning reach to the project ecologist and approval authority before works proceed.

Before habitat disturbance: Avoid and minimise

Avoid direct loss of permanent refuge pools, spawning reaches and the connections between them. The main project risk is not only fish capture, but loss of water, flow, habitat connectivity or water quality.

Redesign works to retain permanent refuge pools, seasonally flowing tributaries, the lower 3 kilometres of the Mitchell River spawning reach and Little Pygmy Creek where these occur in or near the project area.

Maintain surface-water and groundwater inputs that keep refuge pools connected or wet through the dry period.

Retain native streamside vegetation and natural channel form around pools, tributaries and inundated margins.

Avoid activities that increase salinity, sediment, temperature, nutrient loads or turbidity in retained fish habitat.

• Do not drain, fill, isolate or use a refuge pool for construction water without approval and a documented alternatives assessment.
• Keep construction access, laydown areas, stockpiles and spoil out of pools, channels and wetland margins.
• Design crossings to maintain fish passage and the natural timing and volume of flow.
• Treat artificial firefighting or water-supply points used by the species as potential refuge habitat until surveyed.

Before habitat disturbance: Approvals and timing

Confirm the species status under the EPBC Act and Western Australian legislation before finalising the impact assessment. Obtain all required fish collection, animal ethics, clearing, waterway and relocation approvals.

Schedule in-channel disturbance outside the winter to spring breeding and movement period where practicable. If timing cannot be avoided, obtain species-specific advice and approval before works begin.

Stage works so that retained refuge pools and flow paths remain available throughout construction.

• Refer the action under the EPBC Act if the impact may affect this nationally listed species or its habitat.
• Obtain written authorisation before fyke netting, handling, tagging, relocation or other fish collection.
• Include a Little Pygmy Perch risk assessment, survey results, exclusion measures, response actions and reporting requirements in the fauna management plan.
• Use a qualified aquatic ecologist to approve the final work area and construction sequence.

Before habitat disturbance: Pre-clearance preparation

Complete the approved pre-clearance aquatic survey immediately before disturbance, including all permanent pools and connected tributaries within the likely impact area.

Mark no-go areas around retained pools, channels, riparian vegetation and spawning habitat before machinery arrives.

Install exclusion fencing only where it will not block fish movement, flood flows or access to refuge water.

• Brief the fauna spotter catcher, operators, supervisors and subcontractors on the location of fish habitat and the stop-work procedure.
• Prepare clean nets, aerated holding containers, measuring equipment, water-quality equipment and approved release or veterinary contacts before any aquatic work.
• Use clean equipment between waterbodies to reduce transfer of pathogens, weeds and aquatic pests.
• Confirm that dewatering, diversion and temporary crossings have an approved fish rescue and relocation procedure.

During habitat disturbance: Daily controls and machinery coordination

Works near water must be controlled as an aquatic fauna operation. The fauna spotter catcher coordinates with the operator, but fish handling is limited to people with the required authority and skills.

Inspect refuge pools, tributaries, diversion points, sediment controls and exclusion fencing at the start of each shift and after rainfall or flow changes.

Keep machinery out of pools, channels and marked habitat unless the approved method specifically permits entry.

Use a spotter to maintain direct communication with the operator and stop movement before the bucket, blade, vehicle or pump reaches water or habitat.

• Start disturbance only after the fauna spotter catcher confirms that the work area has been checked and the required controls are in place.
• Keep fuels, chemicals, concrete washout, spoil and contaminated water away from all retained aquatic habitat.
• Prevent sudden releases of turbid, saline, hot or contaminated water into pools or tributaries.
• Suspend works if rising water, unexpected flow, fish stranding, a damaged exclusion control or a pollution event could affect retained habitat.

During habitat disturbance: Dewatering and habitat handling

Avoid dewatering permanent refuge pools. If dewatering or isolation is approved, use a staged fish rescue method designed by the aquatic ecologist and authorised by the relevant agency.

Retain natural pool depth, shade, aquatic cover, bank structure and flow paths wherever works affect a channel or pool margin.

Do not remove logs, rocks, root masses or undercut banks from retained pools unless the approved design requires it and replacement habitat is provided.

• Stop pumping if fish are observed in the intake area, stranded in shallow water or exposed to unsuitable water quality.
• Use screened pump intakes and low-flow pumping arrangements where approved to reduce fish entrainment.
• Keep captured fish in clean, aerated water from the capture site and minimise handling and holding time.
• Release fish only to nearby approved retained habitat with suitable water quality and connectivity, not to an isolated or unsuitable pool.

During habitat disturbance: Fish encounter and stop-work response

Stop the local work area if a Little Pygmy Perch is found in the disturbance footprint, a pool is unexpectedly occupied, or fish are stranded or exposed by the works.

Have the aquatic ecologist confirm the identification because the species is similar in appearance to Western Pygmy Perch.

Only authorised and competent personnel may capture, handle, measure, relocate or tag the fish.

• Notify the site supervisor and project ecologist immediately when the species is detected.
• Do not chase, net or relocate fish without the approved method, permit and release location.
• Move injured fish to an approved aquatic wildlife rehabilitator or veterinarian, following the state authority procedure.
• Record the date, time, coordinates, habitat, number and condition of fish, action taken, release location, personnel and photographs.
• Do not recommence work until the project ecologist and approval authority have cleared the area or amended the method.

After habitat disturbance: Immediate checks

Post-work checks must confirm that retained water, flow paths and habitat remain suitable. A completed clearance record is not evidence that a population has been protected if refuge pools have dried or connectivity has been lost.

Inspect the work area, retained pools, tributary connections, banks and sediment controls after each work stage and after significant rainfall.

Check for stranded fish, barriers, new turbidity, changed salinity or conductivity, altered pool depth and blocked movement paths.

Remove temporary crossings, pumps, hoses, fencing and spoil that could prevent movement or alter flow, unless they form part of the approved final design.

• Complete a final aquatic fauna inspection before demobilisation from each work area.
• Photograph and map retained refuge pools, repaired banks, crossings and flow paths.
• Report any fish mortality, habitat damage, pollution, pool loss or unexpected drying under the approval and incident procedures.

After habitat disturbance: Monitoring and reporting

Monitor retained refuge pools and connected breeding habitat through at least the next relevant dry and winter to spring periods where the project altered water regime, channel form, groundwater access or connectivity.

Use the same approved methods and site locations before and after works so that changes in detection, abundance and habitat condition can be assessed.

Give priority to pools supporting known populations, including the two Hay River refuge pools, Kent River refuge pools, Denmark refuge pools and Lake Smith where relevant.

• Repeat water-quality and habitat measurements at the same locations and record flow, pool permanence, salinity or conductivity, temperature and fish detections.
• Use fyke nets or other approved fish methods only under the relevant permits and animal ethics controls.
• Submit monitoring results, incidental records, mortality records and rehabilitation outcomes to the approval authority and relevant state wildlife database.
• Review controls if fish detections, recruitment, refuge permanence or connectivity decline after the works.

After habitat disturbance: Ongoing controls and offsets

Maintain erosion, sediment, pollution and access controls until the site is stable and monitoring shows that retained habitat is functioning.

Keep exclusion fencing and no-go markers in place while they protect retained pools, tributaries or rehabilitation areas, then remove them when they could obstruct fish movement.

If residual impacts remain after avoidance and mitigation, address offset or compensation requirements through the EPBC Act and Western Australian approval processes.

• Do not treat an offset as a substitute for retaining occupied refuge pools, spawning reaches or flow connectivity.
• Document the area, condition and security of any offset or compensatory habitat and link it to the affected population where required.
• Use the project environmental officer's close-out report to confirm approvals, incidents, monitoring, rehabilitation and outstanding actions.

Rehabilitation actions: Restore aquatic habitat and connectivity

Rehabilitation should restore the functions Little Pygmy Perch needs: permanent dry-period water, winter movement, spawning habitat, clean water and connected native stream margins. A planted bank alone will not replace a lost refuge pool or blocked breeding connection.

Reinstate natural channel shape, pool depth, bed material and low-flow connections where construction has altered them.

Restore or protect permanent refuge pools that retain water through summer, with groundwater and surface-water inputs maintained where they occur naturally.

Re-establish uninterrupted connections between refuge pools and seasonally flowing tributaries used for winter breeding.

Design crossings and culverts to maintain fish passage, natural flow timing and suitable low-flow depth.

• Use local native riparian and wetland plants suited to the site, including native sedge and inundation-zone communities where these were present before disturbance.
• Stabilise banks with living vegetation and natural materials rather than hard surfaces where the approved design allows.
• Do not introduce non-local fish, aquatic plants or artificial structures that could favour introduced species or change refuge conditions.
• Reinstate flooded riparian margins and shallow nursery habitat in reaches identified as breeding or larval habitat.

Rehabilitation actions: Retain cover and control threats

Retain natural logs, root masses, rocks, undercut banks and aquatic vegetation that provide cover in refuge pools and channels.

Replace habitat elements removed for access only where the aquatic ecologist confirms that placement will not reduce flow, strand fish or increase erosion.

Control weeds and prevent sediment, nutrients, chemicals and saline drainage from entering rehabilitated pools or tributaries.

Manage introduced fish risks, including Eastern Gambusia, through an approved state-authorised program rather than ad hoc removal.

• Keep stock, vehicles and people out of rehabilitated pools and wetland margins until they are stable and the aquatic ecologist approves access.
• Use fire planning that protects riparian vegetation, refuge pools and wetland margins from damaging fire intensity or loss of shade.
• Do not install nest boxes or terrestrial fauna structures as a substitute for aquatic habitat restoration for this species.
• Inspect rehabilitated sites for drying, salinity increase, barriers, weed invasion and introduced species.

Rehabilitation actions: Success measures and adaptive management

Set site-specific success measures before works begin, based on the pre-work condition and the requirements of the affected population.

Use persistence of permanent refuge water, restored flow connection, suitable water quality, native riparian cover and confirmed fish use as the main measures of functional recovery.

Interpret fish absence with caution because the species moves seasonally and may be absent from flowing reaches outside the breeding period.

Key breeding period to monitor: July to September

Known maximum size for identification: 65 mm total length

Known response to higher discharge: Greater movement and recruitment indicators in the higher-flow year

• Monitor through the dry period and the July to September breeding period where the project affects habitat used by the species.
• Repeat approved fish surveys at the same sites and with recorded effort so results can be compared with baseline data.
• Investigate and correct declining pool permanence, increased salinity, blocked movement, poor recruitment or introduced fish detections.
• Report rehabilitation results and any required corrective works to the relevant approval authority and state wildlife database.

Sources

• Too little but not too late? Biology of a recently discovered and imperilled freshwater fish in a drying temperate region and comparison with sympatric fishes, onlinelibrary.wiley.com: https://onlinelibrary.wiley.com/doi/abs/10.1002/aqc.3346
• Conserving freshwater fish in south-west, WA Department of Biodiversity, Conservation and Attractions: https://library.dbca.wa.gov.au/FullTextFiles/026644.pdf