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Yarra Pygmy Perch (Nannoperca obscura)

The Yarra pygmy perch (Nannoperca obscura) is a small, threatened freshwater fish of southern Australia. It lives in shallow, still or slow-flowing water with dense aquatic vegetation, so clearing, drainage, altered flows, sediment runoff and construction near wetlands, springs, creeks and lakes can affect occupied habitat and downstream populations.

Conservation status

Commonwealth, EPBC Act 1999: Endangered.

Victoria, Flora and Fauna Guarantee Act 1988: Endangered.

Breeding season

The following pattern is a practical guide for southern Australian populations. Timing varies with water temperature, flow and local conditions. Spring breeding habitat should be protected, while late summer and early autumn generally provide better detection after recruitment.

Avoid sampling and disturbance in spring where practicable. For surveys, late summer to early autumn is generally the most effective period, while fish handling must be minimised and undertaken under the required approvals.

  • Breeding: Spawning is reported mainly in September and October at 16 to 24°C. Survey guidance gives a broader breeding season from September to December.
  • Young and recruitment: Species-specific juvenile timing is poorly known. Populations are often easier to detect after recruitment in late summer and early autumn, and the related southern pygmy perch has rapid early development.
  • Local movement and connectivity: This is a non-migratory freshwater fish, but connectivity between permanent waterbodies is needed for local movement, aquatic food webs and recolonisation. Poor dispersal limits recovery after local extinction.
  • Highest clearing risk: Clearing, drainage and hydrology change can damage habitat in any month. Risk is highest during September and October when spawning occurs and submerged vegetation and shallow margins support breeding.

Identification

The Yarra pygmy perch is a very small, laterally compressed freshwater fish. Identification in Victoria and South Australia should be undertaken by an experienced freshwater fish ecologist because it can resemble other pygmy perches.

Adults have an oblong, laterally compressed body, an olive-green to green-brown back and sides, and a yellowish-white underside. The posterior half of the body usually has anteriorly pointing, chevron-shaped markings or a row of dark spots and blotches along the midline.

The single dorsal fin is deeply notched. The lateral line is discontinuous, with separate upper and lower sections. The mouth is small, terminal and oblique, and the eyes sit high on the head. Fins are clear to translucent fawn, often with dark margins.

Maximum length: 75 mm total length

Usual length: Less than 65 mm

Body form: Oblong and laterally compressed

Identification: Distinguishing features

Compared with southern pygmy perch, the Yarra pygmy perch has a straighter head profile, a higher-looking dorsal fin and a slightly notched eye pupil. It lacks the red fin colour shown by southern pygmy perch and variegated pygmy perch.

The lower, free edge of the preorbital bone is straight and strongly serrated. A dark band can extend from the snout through the eye. The tail is slightly rounded.

  • Do not rely on colour alone, as colour varies with condition and breeding state.
  • Use an experienced fish ecologist where Yarra pygmy perch occurs with southern pygmy perch or other small native fish.
  • Treat photographic or visual records as provisional where the diagnostic head, eye, fin and preorbital features cannot be resolved.

Identification: Sex and field signs

During spawning, pelvic fins can turn black. In breeding males, the pelvic fins are reported to turn black, while the dorsal and anal fins can become brown-orange and the leading edge of the anal fin can darken.

The species is free-swimming and does not produce terrestrial tracks, scats, nests, hollows, burrows, calls or sloughs. Presence is normally established by capture or reliable underwater observation in suitable vegetated freshwater habitat.

Fish are sensitive to handling and can lose scales easily. Keep handling to a minimum, use wet hands, and return fish to water promptly under the relevant approvals and animal ethics requirements.

Distribution: National range

The species is endemic to southern Australia and has a fragmented distribution from western Victoria to south-eastern South Australia. Records are concentrated in coastal and near-coastal freshwater catchments, with a separate Murray-Darling Basin evolutionary lineage now extinct in the wild.

The current and historical range extends from the Maribyrnong River system in Victoria, including Deep Creek near Lancefield as the eastern limit, west through Victorian catchments to the Henry Creek catchment in South Australia, about 30 km north of Kingston near Long Bay.

In Victoria, records include the Maribyrnong, Barwon, Corangamite, Hopkins, Portland and Glenelg catchments, as well as eastern subpopulations around the Thompson, Waurn Ponds and Deep Creek areas. In South Australia, the species occurs patchily through the Millicent Coast and adjacent south-eastern freshwater systems.

The Murray-Darling Basin population was confined to Lake Alexandrina and represented a genetically distinct lineage. It is considered extinct in the wild, although individuals are maintained at ex situ sites.

  • Potential habitat in a project area should be assessed even where recent records are absent, because the species is difficult to detect and historical records are incomplete.
  • Downstream wetlands, drainage channels, springs, lakes and slow-flowing reaches should be included when assessing indirect project effects.

Distribution: Strongholds and subpopulations

The species is most common in western Victorian catchments. Reasonable numbers have been recorded around Geelong and Torquay, while Deep Creek supports low numbers at a few isolated sites.

Important Victorian examples include refuges in Thompsons Creek and records from the Curdies River and St Georges River. In Thompsons Creek, Pettavel Road and Horseshoe Bend Road supported fish during the 2006 to 2007 low-flow period, with deeper pools and abundant macrophytes providing refuge.

South Australian and south-western Victorian populations occur in and around karst springs, alkaline fens and other permanent freshwater wetlands. Some sites occur within the Karst Springs and Alkaline Fens of the Naracoorte Coastal Plain Bioregion and Ramsar wetlands including Piccaninnie Ponds Karst Wetlands, Western District Lakes, Glenelg Estuary and Discovery Bay Wetlands.

  • All subpopulations are important because the species has poor dispersal ability and local extinctions can remove genetic diversity.
  • The Bool and Hacks Lagoons population is thought to have been extirpated, with no record since 2012.

Distribution: Population size and trend

The total number of mature individuals is not provided in the available documents. The species has undergone a substantial contraction and fragmentation, with local extinctions in the Yarra River, Dandenong Creek, the Murray-Darling Basin, Mosquito Creek, and Bool and Hacks Lagoons.

The species has an estimated extent of occurrence of about 60,000 km² but an area of occupancy of about 390 km². The restricted area of occupancy reflects the fragmented distribution of suitable habitat.

Estimated extent of occurrence: About 60,000 km²

Estimated area of occupancy: About 390 km²

Evolutionary significant units: Three contemporary lineages, plus one Murray-Darling Basin lineage extinct in the wild

Conservation management units: At least 11, including the ex situ Murray-Darling Basin lineage

Habitat: Waterbody types

Yarra pygmy perch occupies shallow, highly vegetated margins of freshwater wetlands and waterways. Permanent water, aquatic cover and hydrological connection between suitable waterbodies are important habitat attributes.

Habitat includes shallow wetlands, lakes, ponds, springs, creeks and slow-flowing rivers. The species can also occur in artificial drainage channels where suitable freshwater vegetation and water conditions remain.

It is usually found in still or slow-flowing water, although it can prefer slightly stronger streamflow than southern pygmy perch. In karst areas, spring outflows can provide permanent freshwater habitat.

  • Map and inspect all wetlands, spring outlets, drainage channels, creek margins, backwaters and slow-flowing reaches within and downstream of a project area.
  • Include groundwater-dependent habitat where springs or permanent baseflow support shallow freshwater pools.

Habitat: Vegetation and structure

Preferred habitat has abundant submerged and emergent vegetation. Recorded submerged plants include water milfoils, hornwort and eel grass. River club-rush is an example of associated emergent vegetation.

Dense vegetation provides cover and supports aquatic plants and macroinvertebrates on which the species depends. Deep pools and backwaters can provide refuge during drought and low-flow periods.

  • Avoid clearing or trampling submerged, emergent and fringing vegetation.
  • Retain deep pools, backwaters, vegetated margins and connected refuge areas when designing crossings, access tracks, drainage works and temporary work areas.

Habitat: Water and connectivity

Recorded site conditions include pH 4 to 10, salinity below 3000 µS cm−1 and dissolved oxygen above 2 mg L−1. These values describe site suitability reported for the species and are not a substitute for site-specific assessment.

Connectivity between permanent waterbodies supports aquatic plants and macroinvertebrates and reduces the risk of isolated populations being lost. Loss of connectivity can prevent recolonisation because the species is a poor disperser.

pH reported for suitable sites: 4 to 10

Salinity reported for suitable sites: Less than 3000 µS cm−1

Dissolved oxygen reported for suitable sites: More than 2 mg L−1

  • Assess changes to surface flow, groundwater levels, wetland hydroperiod, water quality and connections between pools before works begin.
  • Prevent sediment, contaminated water and altered drainage from entering occupied or potentially suitable habitat.

Habitat: Climate and elevation

The available documents do not provide a defined elevation limit. The species is associated with lowland, shallow freshwater environments in southern Australia, including groundwater-fed karst springs and coastal drainage systems.

Hotter, drier conditions, reduced cool-season rainfall and longer droughts can reduce groundwater recharge, streamflow and the availability of shallow freshwater habitat.

Foraging habitat: Diet

Yarra pygmy perch feeds in freshwater vegetation and near the substrate, where small aquatic prey are concentrated. It is primarily carnivorous and commonly occurs in small groups.

The main prey are insects, insect larvae and planktonic crustaceans. Other species accounts record microcrustaceans, molluscs and aquatic insects, including mosquito larvae.

Dense submerged and emergent vegetation supports aquatic plants and the macroinvertebrate communities that form the fish's food supply.

  • Retain aquatic vegetation and avoid sedimentation that can reduce aquatic plant and macroinvertebrate abundance.
  • Maintain water quality and flow conditions that support aquatic invertebrates in occupied and connected habitat.

Foraging habitat: Foraging areas and range

The species forages in shallow, still or slow-flowing vegetated margins of wetlands, lakes, ponds, springs, creeks and drainage channels. In the Murray-Darling Basin it used slow-flowing or still water around fringing reedbeds and submerged aquatic vegetation.

A specific foraging range or home range has not been reported. Fragmented populations and poor dispersal indicate that local habitat quality and connectivity are more important assessment considerations than a fixed movement distance.

  • Survey vegetated margins, backwaters and shallow pools rather than relying only on the main channel.
  • Treat aquatic vegetation used by feeding fish as habitat, even where fish are not observed during a single visit.

Breeding habitat: Breeding biology

Breeding occurs in freshwater during spring, in warm water and among submerged vegetation. Detailed information on courtship, egg numbers and early development remains limited.

Spawning occurs in spring, mainly in September and October, when water temperatures are 16 to 24°C. Survey guidance identifies a broader breeding season from September to December.

The species is assumed to lay demersal, non-adhesive eggs over submerged aquatic vegetation and substrate, based on the breeding biology of the closely related southern pygmy perch. Larvae of that related species hatch after 2 to 4 days.

Spawning season: Mainly September and October; survey guidance gives September to December

Spawning temperature: 16 to 24°C

Egg type: Demersal and non-adhesive, inferred from southern pygmy perch

Egg or larval development: Larvae of the related southern pygmy perch hatch after 2 to 4 days

Clutch size: Not reported

Age at maturity: Within one year, inferred from southern pygmy perch

Lifespan: Approximately 1 to 5 years, inferred from southern pygmy perch

Generation time: Approximately 2 years, inferred from southern pygmy perch

  • Avoid disturbing breeding habitat during spring where practicable, particularly submerged vegetation and shallow margins.
  • Do not use the absence of visible eggs as evidence that breeding habitat is not present, because eggs are demersal and non-adhesive and species-specific breeding information is limited.

Breeding habitat: Breeding habitat features

Breeding habitat is expected to comprise shallow freshwater with submerged aquatic vegetation and suitable substrate. Dense vegetated margins, spring outflows, wetland edges, pools and slow-flowing reaches can provide the required structure.

Freshes and adequate water levels help maintain habitat and water quality. Prolonged low flows can isolate pools, reduce cover and compromise spawning and recruitment over successive seasons.

  • Retain submerged vegetation, shallow margins, stable substrate and adequate water levels during the breeding period.
  • Protect spring flows, wetland inflows and connected refuge pools from extraction, drainage, sediment deposition and construction disturbance.

Sheltering habitat: Aquatic refuges

The species shelters within dense aquatic vegetation, shallow vegetated margins, reedbeds, backwaters and deeper pools. It does not use terrestrial dens, hollows, burrows or roosts.

Submerged and emergent vegetation provides cover from predators and supports the aquatic food web. In the Murray-Darling Basin, fringing reedbed refuge habitat became isolated as lake levels fell, contributing to local extinction.

Deep pools and backwaters can provide refuge during drought and low-flow periods. In Thompsons Creek, sites with significant macrophytes and deeper pools remained important refuge areas during the 2006 to 2007 drought.

  • Retain and protect dense macrophyte beds, fringing reedbeds, deep pools and backwaters.
  • Keep refuge pools connected to other permanent waterbodies where possible.
  • Do not assume an unvegetated shallow margin is suitable refuge solely because water is present.

Sheltering habitat: Shelter limitations

No species-specific dimensions for refuge pools, vegetation beds or sheltering structures are provided. The species is a free-swimming fish and has no known terrestrial shelter, nest, burrow, hollow, roost, track or scat.

Loss of vegetation, falling groundwater, wetland drainage and reduced flow can remove cover and expose fish to predators, poor water quality and isolation.

  • Include aquatic refuge habitat in pre-clearing inspections and construction exclusion zones.
  • Manage temporary water diversions and dewatering so fish are not stranded in isolated pools or removed from connected habitat.

Threats: Clearing, construction and fragmentation

The main project risks are loss and fragmentation of shallow freshwater habitat, altered surface and groundwater hydrology, vegetation removal, sediment and water-quality impacts, and introduction or spread of predatory or competing fish.

Wetland drainage, infilling, land clearing and urban development have reduced and fragmented habitat. Ongoing development near Melbourne, Geelong and Torquay is identified as a major threat to eastern subpopulations.

Most populations are isolated and the species has poor dispersal ability. Local extinctions are therefore unlikely to be repaired by natural recolonisation and can remove genetic diversity.

Potential distribution loss from eastern urban-fringe subpopulation losses: About 40% reduction in extent of occurrence and about 20% reduction in area of occupancy

  • Avoid clearing, infilling or modifying known subpopulation habitat and adjoining suitable habitat.
  • Assess direct and downstream effects on wetlands, springs, creeks, lakes, drainage channels and connected pools.
  • Use buffers and exclusion zones around aquatic and riparian habitat, with distances set by the project risk assessment and relevant approvals.

Threats: Hydrology and water quality

Impoundments, groundwater extraction, wetland drainage, river regulation, land clearing and urban development can alter flow volume, flow seasonality, groundwater levels and wetland hydroperiod.

Stock access, construction runoff and loss of riparian vegetation can increase sediment, turbidity, nutrient pollution and water temperature. Sediment can smother eggs, reduce prey habitat and slow streamflow.

Drought and reduced cool-season rainfall compound these effects by reducing recharge, streamflow, connectivity and permanent water.

  • Maintain surface flows, groundwater-dependent spring discharge, water levels and connections between pools.
  • Control sediment, turbid water, concrete washout, hydrocarbons and other pollutants during works.
  • Fence or otherwise exclude stock from occupied wetlands and vegetated stream margins where relevant.
  • Retain or restore riparian vegetation to provide shade and reduce sediment and nutrient inputs.

Threats: Predators, competitors and disease

Introduced redfin perch, brown trout and rainbow trout are suspected predators. Eastern gambusia may compete with pygmy perch, while common carp can damage aquatic vegetation.

Stocking of native fish may create additional competition or predation risk where stocked fish spread into Yarra pygmy perch habitat. Illegal aquarium collection is a possible emerging threat to small, restricted subpopulations.

Disease and biosecurity risks are relevant to translocation and captive programs, although a specific disease threat to wild Yarra pygmy perch is not identified in the available documents.

  • Prevent the movement of introduced fish, water, equipment and biological material between catchments.
  • Use washdown and aquatic hygiene procedures for nets, electrofishing equipment, pumps, vehicles and temporary water-holding containers.
  • Report suspected illegal collection or introduced fish incursions through the relevant state system.

Threats: Fire and coastal processes

More frequent or severe fire can increase water temperature, alter water chemistry and deliver ash and sediment to waterways after rainfall. Sediment slugs can travel up to 80 km downstream from burnt areas.

Sea-level rise and storm surges may cause saline intrusion into low-lying freshwater wetlands, karst springs and connected aquifers.

Reported downstream reach of post-fire sediment slugs: Up to 80 km

  • Install erosion and sediment controls after fire or earthworks, especially before forecast rainfall.
  • Protect riparian vegetation and avoid activities that increase ash, sediment or saline runoff to freshwater habitat.
  • Include tidal or saline intrusion risk in assessments for low-elevation coastal wetlands and karst spring systems.

Survey methodology: 1. Map habitat and plan the survey

Survey all suitable freshwater habitat that may be affected directly or indirectly, including downstream wetlands, pools, drainage channels and connected waterways. Yarra pygmy perch are small, cryptic fish associated with highly vegetated margins of still or slow-flowing freshwater, and absence from a single survey should not be treated as proof of absence.

Define the project area and all areas that may be affected by altered flows, drainage, sediment, groundwater changes or downstream impacts.

Map shallow wetlands, lakes, ponds, springs, creeks, slow-flowing rivers and artificial drainage channels, together with submerged and emergent aquatic vegetation.

Prioritise dense stands of water milfoils, hornwort, eel grass and river club-rush, and areas with permanent water, deeper pools, backwaters or connected refuge habitat.

Record water depth, flow, aquatic vegetation, riparian condition, barriers, stock access, turbidity, salinity, dissolved oxygen and nearby introduced fish habitat where practicable.

Typical adult size: Maximum total length 75 mm

Suitable water chemistry reported in the conservation advice: pH 4 to 10, salinity below 3000 µS cm⁻¹ and dissolved oxygen above 2 mg L⁻¹

Known distribution: Patchy coastal and inland drainage systems from the Maribyrnong River system in Victoria to the Henry Creek catchment in South Australia

  • Use current state and Australian Government databases, local records, published literature, threatened species teams and local fish experts to identify known and historical records.
  • Treat historical range records cautiously because habitat loss has contracted the species range and local populations may be extinct or isolated.

Survey methodology: 2. Backpack electrofishing

Use backpack electrofishing in wadeable wetlands, shallow flowing streams, riffles and lake margins, following the Australian Code of Electrofishing Practice and the project approval conditions.

Where practicable, sample a measured 100 m reach and complete two electrofishing runs, as used in Victorian fish surveys, while adapting reach length to site access, habitat and safety requirements.

Use a fine mesh seine with an attached bag or cod end downstream of the electrofishing area where suitable, and use a dip net to collect fish that are missed.

Keep electrofishing intensity and handling time as low as practicable because pygmy perches are small, sensitive and easily stressed.

Do not use boat-based electrofishing as the default method for this small south-eastern Australian freshwater fish group.

Victorian example effort: A 100 m reach, sampled twice, with each run lasting 30 to 45 minutes

Best habitat for this method: Wadeable still water, shallow flowing streams and riffles

  • Avoid electrofishing through dense vegetation where the gear would damage macrophytes or destabilise the bank.
  • Measure and record the reach length, electrofishing duration, number of runs, water conditions, habitat sampled, effort and all fish captured.

Survey methodology: 3. Traps, fyke nets, seines and dip nets

Use a combination of methods where access, water depth, vegetation or conductivity limits electrofishing, because detection varies with habitat and gear.

Set collapsible bait traps, approximately 250 by 250 by 450 mm with 3 mm mesh, for 30 to 60 minutes and check them thoroughly.

Use fyke nets perpendicular to vegetated banks where appropriate, and secure overnight sets so that captured animals remain able to breathe and are protected from avoidable mortality.

Use small two-person seines with 2 to 5 mm mesh only where necessary, taking care not to disturb littoral or submerged vegetation.

Use fine mesh dip nets in very shallow water or where other gear cannot be deployed, including triangular dip nets with mesh as fine as 1.5 mm where approved and suitable.

Keep captured fish in a container part full of site water for the shortest practicable time, identify and measure them promptly, then return them to the capture location unless an approved translocation or rescue action applies.

Reported fyke net use: Fyke nets set perpendicular to banks where macrophyte vegetation was present

Reported overnight survey use: Fyke nets were set overnight at seven Victorian sites under relevant approvals

  • Avoid seine netting where electrofishing or trapping is practicable because it can disturb habitat and is associated with higher mortality.
  • Check all traps and nets at the frequency required by the approval, and remove non-target fauna immediately.
  • Do not place gear where it blocks fish passage or damages submerged vegetation.

Survey methodology: 4. Timing, identification and detection limits

Schedule the main survey in mid to late summer or early autumn, when capture is reported to be easiest after recruitment and water levels are more concentrated.

Avoid spring, particularly September and October, where possible because this is the reported breeding and spawning period.

Late autumn and winter can reduce disturbance to breeding fish, but detection may be poorer, especially in mid-winter when water levels are high.

Use an experienced freshwater fish ecologist or ichthyologist where pygmy perch identification is uncertain because Yarra pygmy perch can be difficult to distinguish from southern pygmy perch and other pygmy perches in Victoria and South Australia.

Photograph representative fish and retain sufficient diagnostic information for verification, using approved non-lethal procedures.

Breeding period reported in the survey guideline: Spring, with September to October specifically identified as a period to avoid

Preferred capture period reported in the survey guideline: Mid to late summer, especially after recruitment, extending into early autumn

  • Do not conclude that the species is absent solely because it was not captured in one visit, particularly during high flows, deep water, dense vegetation or outside the preferred capture period.
  • Record sympatric southern pygmy perch, redfin perch, trout, carp and eastern gambusia because these species inform habitat condition and threat assessment.
  • Handle fish with wet hands, minimise contact, keep them in water while out of the habitat and release them promptly at the capture site.

Survey methodology: Minimum effort and reporting

  • Survey every suitable waterbody, wetland margin, vegetated pool, drainage channel and connected reach that may be disturbed or affected downstream.
  • Use at least two complementary detection methods where practicable, selected from backpack electrofishing, traps, fyke nets, dip nets and carefully controlled seine netting.
  • Record survey dates, start and finish times, weather, water level and flow, water quality, gear type, mesh size, soak or fishing time, reach length, number of runs, habitat condition and effort for each method.
  • Record all captures, non-detections, bycatch, mortalities, injuries, photographs, coordinates and release locations.
  • Submit confirmed records and survey results to the relevant state or territory wildlife or biodiversity database, and provide records required by the Australian Government approval or referral process.
  • Report a suspected new population, an unexpected concentration of fish, a dead or injured listed fish, or a material change to retained habitat to the project environmental officer and the relevant regulator.

Before habitat disturbance: Avoid and minimise habitat loss

Treat any suitable, connected freshwater habitat as potentially important because all Yarra pygmy perch populations are considered important for recovery and the species has poor dispersal capacity. Avoid direct loss first, then reduce changes to water levels, flow, water quality and vegetation.

Habitat type: Highly vegetated margins of still or slow-flowing wetlands, lakes, ponds, springs, creeks and rivers

Connectivity requirement: Connectivity between permanent waterbodies supports aquatic plant and macroinvertebrate lifecycles and reduces fragmentation

  • Retain known and potential subpopulations, shallow vegetated margins, permanent pools, backwaters, springs, wetlands, slow-flowing reaches and adjoining similar habitat.
  • Avoid clearing or filling aquatic and riparian vegetation used for cover, including water milfoils, hornwort, eel grass and river club-rush.
  • Maintain surface water and groundwater contributions, natural flow patterns, water levels and connectivity between permanent waterbodies.
  • Keep machinery, spoil, concrete washout, fuels, chemicals and sediment out of the waterway and its flood-prone margins.
  • Avoid works that could lower groundwater, drain wetlands, isolate pools, increase salinity, reduce dissolved oxygen or increase turbidity.
  • Retain habitat adjoining known sites so that natural range extension or an approved translocation remains possible.

Before habitat disturbance: Approvals and work planning

National listing: Endangered under the EPBC Act, effective from 15 November 2023

Victorian listing supplied for this profile: Endangered

  • Check whether the proposed action is likely to significantly impact this EPBC Act listed species or its habitat, and obtain project-specific Australian Government approval or referral advice before works commence.
  • Check Victorian and South Australian threatened species, fish, wildlife, waterway and translocation requirements where relevant to the site.
  • Obtain any scientific, collection, electrofishing, handling, salvage, relocation or release permits needed for the proposed survey and fauna management work.
  • Prepare a fauna management plan that identifies habitat, survey methods, authorised personnel, exclusion zones, stop-work triggers, fish handling, rescue, release, incident reporting and emergency contacts.
  • Stage works to retain connected water and refuge pools throughout construction, and schedule in-water disturbance outside the spring breeding period where practicable.
  • Consult the relevant species recovery team, state agency, Traditional Owners and local freshwater fish experts when works affect a known population or genetically distinct management unit.

Before habitat disturbance: Prepare the site

  • Complete a targeted pre-clearance fish survey before removing aquatic vegetation, draining water, diverting flow, isolating a pool or starting works near suitable habitat.
  • Mark no-go areas, retained pools, vegetated banks, springs, groundwater-dependent features, access routes and sediment control structures before machinery enters the site.
  • Install exclusion fencing or other physical controls where they can keep machinery, vehicles, stock and people out of retained aquatic habitat without blocking fish passage or flood flows.
  • Inspect the work area for connected downstream habitat and plan controls for dewatering, pumping, cofferdams, temporary crossings, spoil placement and stormwater discharge.
  • Prepare clean, fish-safe equipment and dedicated containers, nets and holding water for any approved capture and rescue operation.
  • Brief all operators and spotter catchers on the species' small size, identification from southern pygmy perch, habitat indicators and the requirement to stop for unexpected fish or habitat impacts.

During habitat disturbance: Daily controls and machinery interface

Use a fish-focused fauna spotter catcher for works that can affect water, aquatic vegetation, banks or flow. The spotter catcher must have the authority and equipment to stop work before fish are stranded, injured or exposed to poor water quality.

Relevant water-quality thresholds from the conservation advice: Reported site suitability includes dissolved oxygen above 2 mg L⁻¹ and salinity below 3000 µS cm⁻¹

  • Inspect exclusion fencing, sediment controls, pumps, screens, diversion structures and retained pools before work starts each day and after rainfall or flow changes.
  • Keep machinery outside marked aquatic exclusion zones unless the approved method statement specifically permits entry.
  • Use a spotter catcher to maintain a clear view of the work face, water edge, dewatering area and downstream discharge point while machinery is operating.
  • Stop machinery immediately when the spotter catcher signals, and do not resume until the animal, habitat issue or water-quality risk has been assessed and controlled.
  • Prevent dirty water, concrete, hydrocarbons, fine sediment, ash, fertiliser and other pollutants from entering retained or downstream habitat.
  • Maintain fish passage and avoid rapid drawdown, stranding, sudden temperature changes and low dissolved oxygen in isolated water.

During habitat disturbance: Fish rescue and handling

Genetic structure: At least 11 conservation management units have been defined, including the Murray-Darling Basin, Central, Merri and Eastern evolutionary significant units

Murray-Darling Basin status: The Murray-Darling Basin lineage is considered extinct in the wild and is maintained at ex situ sites

  • If fish must be removed from an approved work area, use only authorised personnel trained in freshwater fish identification, electrofishing, netting and animal welfare.
  • Use wet hands, soft or appropriate fine mesh gear and site water, and minimise air exposure, contact and holding time.
  • Place rescued fish in aerated containers of suitable site water, keep species and capture locations recorded, and prevent mixing between management units unless the approved translocation plan permits it.
  • Release healthy fish into nearby retained habitat only where the release location is approved, suitable, connected or otherwise addressed by an approved translocation plan.
  • Do not move fish between catchments, wetlands or genetic management units as an improvised response to construction impacts.
  • Place injured or moribund fish in suitable clean water and obtain advice from the project veterinarian, wildlife carer, fisheries authority or other authorised wildlife professional.

During habitat disturbance: Habitat features, triggers and records

Maximum reported total length: 75 mm

Size range recorded in a Victorian Otways survey: 33 to 62 mm at Thompsons Creek

  • Treat vegetated shallow margins, springs, outlet streams, permanent pools, backwaters, drainage channels, submerged macrophyte beds and riparian buffers as fish habitat features requiring protection.
  • Do not remove aquatic vegetation, drain a pool, alter a spring outlet, block a connected channel or disturb the bed and bank unless the action is authorised and the fauna management plan covers it.
  • Stop work for any Yarra pygmy perch capture, fish stranding, fish mortality, unexpected population concentration, damaged retained habitat, uncontrolled sediment release, fish passage blockage or water-quality deterioration.
  • Record the date, time, coordinates, activity, machinery, observer, species, number, life stage or size, condition, capture and release locations, photographs, water conditions, action taken and approvals relied upon.
  • Notify the project environmental officer and relevant regulator of a listed fish capture, injury, mortality, unauthorised habitat impact or failure of a control, in accordance with approval conditions.
  • Keep all rescue, handling, relocation, mortality, incident and corrective-action records with the project environmental records.

After habitat disturbance: Complete and verify the site

The work is not complete when machinery leaves the site. Confirm that fish were not stranded, that retained habitat remains connected and vegetated, and that construction has not changed water quality or flow beyond the approved limits.

  • Inspect all dewatered areas, isolated pools, diversion channels, pump intakes, sediment basins, spoil edges and downstream margins for stranded, injured or dead fish before demobilisation.
  • Remove temporary barriers only when safe fish passage and suitable water levels have been restored.
  • Remove construction debris, silt deposits, spoil and temporary structures from retained aquatic habitat without damaging macrophytes or the bed and bank.
  • Check that retained pools hold water, aquatic vegetation remains in place, riparian buffers are intact and flow paths are not blocked or newly diverted.
  • Complete a post-clearance fish survey where required by the fauna management plan, approval or incident response, using methods appropriate to the remaining habitat and season.

After habitat disturbance: Monitor and report

  • Monitor water level, flow, turbidity, salinity, dissolved oxygen, aquatic vegetation, fish passage and sediment controls at the frequency specified in the approval or management plan.
  • Undertake follow-up surveys after the next suitable survey period and after major flow, drought, fire or construction events where the risk assessment identifies a need.
  • Compare post-work fish records and habitat condition with pre-work records, including effort, gear, reach length, capture numbers and non-detections.
  • Report all captures, mortalities, injuries, control failures, habitat changes, corrective actions and monitoring results to the project environmental officer, approval holders and relevant state or Australian Government agencies.
  • Submit verified species records to the relevant state or territory wildlife database and retain the data, photographs and chain of custody for specimens or genetic material.

After habitat disturbance: Offsets and corrective action

  • Apply any offset, compensatory habitat action, conservation payment or recovery action required by the EPBC Act approval or state approval.
  • Do not use an offset as a substitute for retaining known habitat, maintaining connectivity or preventing avoidable mortality.
  • If monitoring shows declining fish numbers, loss of aquatic vegetation, reduced flow, poor water quality or failed recruitment, implement the approved corrective action and notify the relevant regulator.
  • Consider targeted habitat restoration, stock exclusion, riparian fencing, flow management, invasive fish control or an approved rescue and translocation response where the conservation advice identifies these actions as appropriate.

Rehabilitation actions: Restore water and habitat structure

Rehabilitation should restore permanent or seasonally reliable freshwater habitat, dense aquatic and riparian cover, water quality and connectivity. Design the works for a small, non-migratory fish that recolonises poorly and is vulnerable to drought, altered hydrology and introduced fish.

Reported habitat plants: Myriophyllum species, Ceratophyllum demersum, Vallisneria australis and Schoenoplectus validus

Habitat water-quality guide: pH 4 to 10, salinity below 3000 µS cm⁻¹ and dissolved oxygen above 2 mg L⁻¹

  • Reinstate or protect shallow vegetated margins, deeper pools, backwaters and low-velocity refuge areas adjoining retained habitat.
  • Restore natural surface flow and groundwater interactions where works have altered water levels, recharge, discharge or seasonal connectivity.
  • Design wetlands and drainage features to retain water all year where practicable, while maintaining suitable shallow margins and connected refuge habitat.
  • Replant locally appropriate native aquatic and emergent vegetation, including water milfoils, hornwort, eel grass and river club-rush where these species suit the site and regional provenance requirements.
  • Restore shaded riparian vegetation to reduce water temperature, stabilise banks, reduce sediment and nutrient entry and protect aquatic vegetation.
  • Do not introduce non-local fish or use stocking as part of rehabilitation unless specifically approved.

Rehabilitation actions: Control stock, weeds, predators and fire impacts

  • Install and maintain riparian fencing to prevent stock trampling, removal of vegetation, sediment input, faecal pollution and increased water temperature from loss of shade.
  • Control pest plants and animals without disturbing retained aquatic habitat or contaminating water.
  • Assess and control redfin perch, brown trout, rainbow trout, carp and eastern gambusia where they threaten the restored population, using methods approved by the relevant authority.
  • Inspect restored reaches after bushfire and rainfall, and install erosion and sediment controls before ash and debris can enter pools and downstream wetlands.
  • Restore burnt riparian vegetation and ensure fire prevention or fuel-reduction activities do not damage known or potential fish habitat.
  • Maintain weed, stock, predator and sediment controls until monitoring shows that the site is stable.

Rehabilitation actions: Monitor success

Indicative generation time: Approximately 2 years, inferred from the related southern pygmy perch

Reported reintroduction outcome in the Murray-Darling Basin: Reintroductions in 2012 and 2015 were unsuccessful, and the lineage is now extinct in the wild there

  • Set measurable success criteria for water retention, flow connectivity, aquatic vegetation cover, riparian establishment, water quality, fish passage and Yarra pygmy perch detection.
  • Repeat standardised fish surveys using comparable gear, effort, reach length, season and habitat coverage so that changes in detection and abundance can be interpreted.
  • Use late summer to early autumn surveys to assess recruitment and detection where this timing is practicable, while avoiding unnecessary disturbance during September and October spawning.
  • Investigate repeated non-detection, recruitment failure, declining aquatic vegetation, reduced dissolved oxygen, increasing salinity, drought stress or introduced fish presence.
  • Maintain monitoring and adaptive management for the period required by the approval, and report results to the relevant state wildlife database and approval agencies.
  • Consider an approved captive breeding, temporary salvage or translocation response only where a subpopulation faces high extirpation risk and in accordance with the relevant genetic and translocation strategy.

Sources