Fauna Spotters logo

Ewens Pygmy Perch (Nannoperca variegata)

The Ewens Pygmy Perch, Nannoperca variegata, is a small freshwater fish restricted to south eastern South Australia and south western Victoria. It uses clear, shallow, flowing water with abundant submerged or emergent vegetation, so works near creeks, ponds, wetlands and drainage lines can affect habitat, water quality and flow conditions. It is listed as Vulnerable under the EPBC Act and Endangered in Victoria.

Conservation status

Commonwealth, EPBC Act 1999: Vulnerable.

Victoria, Flora and Fauna Guarantee Act 1988: Endangered.

Breeding season

The seasonal pattern below is based on the documented spring to early summer breeding period and the survey guidance for threatened pygmy perches. The timing of young fish, dispersal and peak abundance is not described specifically for Ewens Pygmy Perch, so those rows identify the evidence limit rather than assigning unsupported months.

Exact monthly spawning, recruitment, movement and young-fish periods are not available for Ewens Pygmy Perch in the supplied documents. Confirm timing with the relevant state authority and a qualified freshwater fish ecologist before works.

  • Breeding: Spawning is reported from spring to early summer. September to November is shown as the likely peak period, with December still possible, but the sources do not define monthly peak intensity.
  • Young: Young fish would be expected after spawning, but the supplied documents do not provide a hatching, recruitment or dependent-young period for this species. These months are indicative only and should not replace site-specific advice.
  • Survey conditions: For Victorian threatened fish generally, December to April is reported as a good survey period because flows are lower. The pygmy perch guidance also recommends minimising disturbance to breeding populations and habitats, with late autumn and winter preferred for some breeding pygmy perch surveys.
  • Highest clearing risk: Spring to early summer carries the highest documented risk because spawning occurs then and eggs may be associated with submerged vegetation and substrate. Disturbance to occupied habitat can also harm fish outside this period, so timing does not remove the need for aquatic habitat controls.

Identification

This is a very small, perch-like fish that is most likely to be found in clear, vegetated freshwater rather than in open, silty water. Identification should be confirmed by an appropriately experienced freshwater fish ecologist, especially where Southern Pygmy Perch or Yarra Pygmy Perch also occur.

The body is oblong and compressed. It has a single deeply notched dorsal fin, a divided lateral line, a curved dorsal head profile and a small terminal mouth. Colour varies from bright green or olive on the back, through tan or light brown on the sides, to a whitish or orange belly. The head, back and pectoral area may be golden, with a dark spot at the base of the caudal fin and a series of dark midlateral blotches.

Maximum length: 65 mm total length

Body form: Oblong and laterally compressed

Key markings: Dark caudal-fin-base spot and dark midlateral blotches

Identification: Similar species

The Ewens Pygmy Perch resembles the more common Southern Pygmy Perch, Nannoperca australis, and may occur with Southern Pygmy Perch and Yarra Pygmy Perch, Nannoperca obscura. Habitat can assist with field assessment: Ewens Pygmy Perch generally prefers faster flowing water, including channels linking ponds, whereas Southern Pygmy Perch is more associated with pool habitat. This is a field aid, not a substitute for taxonomic confirmation.

Identification: Field signs and sex

There are no documented tracks, scats, calls, nests, sloughs or eyeshine. The species is free swimming and is normally detected by direct capture in suitable aquatic habitat. The supplied documents do not provide reliable external features for distinguishing males from females, or a species-specific field sign that remains after the fish has moved away.

Distribution: National range

The species has a very restricted range in south eastern Australia. Records are concentrated in a small number of river, creek, pond and wetland systems in two states.

In Victoria, the species is restricted to the Glenelg River system in the far south west. In South Australia, it occurs in the Ewens Ponds, Piccaninnie Ponds and Eight Mile Creek systems in the far south east. FishBase also identifies Ewens Ponds near Mount Gambier and a small creek at Winnap in the Glenelg River system.

States: Victoria and South Australia

Victorian region: Glenelg River system, far south west

South Australian region: Ewens Ponds, Piccaninnie Ponds and Eight Mile Creek systems, far south east

Broad climate and latitude: Temperate; FishBase gives approximately 36 to 37 degrees south

  • Treat suitable clear, shallow, vegetated streams, pond connections and associated wetlands within these systems as potential habitat until assessed.
  • Include downstream areas and connected waterways that could be affected by changes in flow, sediment, groundwater or water quality.

Distribution: Strongholds and subpopulations

Known locations include permanent waterways such as the Glenelg and Wannon rivers, Grange Burn Creek, Ewens Ponds, Piccaninnie Ponds and Eight Mile Creek. The recovery plan recorded 20 locations in Victoria and South Australia, but the total population size was not known. Only two of those 20 populations occurred in some form of reserve, at Ewens Ponds and Piccaninnie Ponds; the other 18 were on private land, generally used for grazing.

Recorded locations in the recovery plan: 20

Locations in reserves: 2

Locations outside reserves: 18

Recorded count at a 100 metre reach: Up to 187 individuals at Grange Burn Creek

Very small population example: Two specimens recorded from the 54 foot pond population in South Australia

Distribution: Population trend

The recovery plan reports a likely significant decline in abundance associated with river and creek habitat alteration and groundwater extraction. The decline was considered to be continuing, with at least one population becoming extinct in recent decades. Total abundance and current population sizes were not known in the supplied documents.

Habitat: Waterways and substrates

Ewens Pygmy Perch uses shallow, clear freshwater with moderate to high flow and dense aquatic vegetation. It can tolerate slightly brackish water, but the preferred habitat described in the recovery plan is freshwater.

Preferred sites are relatively shallow streams with moderate to high water flow. The species is strongly associated with submerged and emergent aquatic vegetation and has a preference for clear water. It is usually found over gravel, cobble or boulder substrates where silt is absent, although at Ewens Ponds it is associated with substantial detritus.

Water type: Freshwater, with tolerance of slightly brackish water

Flow: Moderate to high water flow preferred

Water clarity: Clear water preferred

Substrate: Usually gravel, cobble or boulder with little silt

Wild temperature range: 14 to 26 degrees Celsius

Wild pH range: 6.8 to 7.5

  • Inspect shallow flowing reaches, riffles, creek margins, pond outlets and channels linking ponds.
  • Map submerged and emergent vegetation, gravel, cobble, boulder, woody debris and accumulated detritus before works begin.
  • Assess upstream and downstream habitat where construction could alter sediment movement or flow.

Habitat: Vegetation and associated habitat

The species is normally closely associated with submerged and emergent aquatic vegetation. It may occur in small groups, sometimes with Southern Pygmy Perch and Yarra Pygmy Perch. In the Ewens Ponds system, Ewens Pygmy Perch was most abundant in faster flowing channels connecting ponds, while Southern Pygmy Perch was more abundant in pools.

Habitat: Site assessment limits

The supplied documents do not provide an elevation range, a defined vegetation community classification or a minimum vegetation patch size. Habitat assessment should therefore focus on hydrology, water clarity, substrate, aquatic vegetation and connectivity rather than on elevation or a fixed vegetation area.

Foraging habitat: Diet

The species is primarily carnivorous and feeds within shallow, vegetated freshwater habitat. The available sources describe its prey, but do not provide a measured home range, daily movement distance or feeding territory.

Aquatic insects and benthic microcrustaceans make up the bulk of the diet. The species is free swimming and uses water associated with submerged and emergent vegetation.

Main prey: Aquatic insects

Other main prey: Benthic microcrustaceans

Feeding habitat: Clear, shallow, vegetated freshwater, especially flowing reaches

  • Retain aquatic vegetation, shallow margins, gravel and cobble habitat, and clean interstitial spaces that support aquatic invertebrates.
  • Prevent sediment entry and changes in flow that could smother benthic habitat or reduce aquatic invertebrate prey.

Foraging habitat: Foraging area

No species-specific foraging range or feeding distance is given. Because the fish occurs in small groups and is associated with connected flowing reaches, pond-linking channels and adjacent vegetated margins should be assessed as part of the available foraging habitat, not only the point where a fish is captured.

Breeding habitat: Breeding biology

Breeding occurs from spring to early summer, but the wild breeding biology of this species is poorly known. The available evidence indicates that submerged vegetation and substrate provide the spawning surface or immediate spawning habitat.

The species is reported to spawn from spring to early summer. The recovery plan assumes that its breeding behaviour is similar to Southern Pygmy Perch, which lays demersal, non-adhesive eggs over submerged aquatic vegetation and the substrate. Egg number, incubation period, age at maturity and lifespan are not provided in the supplied documents.

Breeding season: Spring to early summer, approximately September to December

Egg placement: Demersal and non-adhesive, probably over submerged aquatic vegetation and substrate based on the recovery plan comparison with Southern Pygmy Perch

Clutch or egg number: Not reported in the supplied documents

Incubation period: Not reported in the supplied documents

Age at maturity: Not reported in the supplied documents

Lifespan: Not reported in the supplied documents

Estimated generation time: 1.5 years, FishBase estimate

Breeding habitat: Breeding habitat features

Potential breeding habitat includes shallow, clear, flowing water with submerged aquatic vegetation and suitable gravel, cobble or boulder substrate. Disturbance to vegetation, substrate or water quality during spring and early summer may affect spawning habitat and eggs. The exact spawning sites used by wild populations are not described.

  • Avoid disturbing submerged vegetation and the bed of occupied or potentially occupied reaches during the spring to early summer breeding period where practicable.
  • Control sediment, dewatering and flow changes so that eggs and spawning surfaces are not exposed, buried or washed away.
  • Survey connected channels and vegetated margins, not only open pond water.

Sheltering habitat: Cover used by fish

No discrete den, burrow, hollow or nest is used. Shelter is provided by aquatic structure within the waterway, particularly submerged and emergent vegetation, woody debris and complex substrates.

The species is normally closely associated with submerged and emergent aquatic vegetation. FishBase also reports association with accumulated flood debris and log snags. The recovery plan describes occurrence over gravel, cobble or boulder, and at Ewens Ponds in areas with large amounts of detritus.

Known cover: Submerged and emergent aquatic vegetation

Additional structure: Accumulated flood debris and log snags

Substrate cover: Gravel, cobble, boulder and, at Ewens Ponds, substantial detritus

Shelter dimensions: No species-specific refuge size is reported

  • Retain submerged and emergent vegetation within and beside the work footprint.
  • Avoid removing log snags, accumulated flood debris or coarse substrate unless a specific ecological assessment supports the action.
  • Maintain water depth and flow around cover during construction and operation.

Sheltering habitat: Handling and refuge protection

Threatened fish in this group are sensitive and easily stressed, and their scales are easily lost. If capture is required, use wet hands, minimise contact, keep fish out of the water for the shortest possible time and hold them in a container of water before release. Sampling should avoid modifying fish communities and their habitat.

  • Use an appropriately experienced fish ecologist or fauna spotter catcher for capture and relocation decisions.
  • Do not rely on passive mesh nets where they may cause mortality or capture non-target fauna.
  • Follow approved animal ethics, fisheries and electrical fishing requirements for any electrofishing work.

Threats: Hydrology and habitat change

The main documented threats are hydrology change, habitat alteration, grazing damage, poor regeneration, climate change and introduced fish. Clearing and construction can add direct risks through removal of aquatic vegetation, disturbance of substrates, sediment input, dewatering and changes to connected flows.

Wetland drainage and groundwater extraction are identified threats. Habitat alteration in rivers and creeks has contributed to decline, and the recovery plan reports that the decline may be continuing. Flow, groundwater and water quality controls are therefore relevant to works near occupied or connected habitat.

  • Do not drain, dewater or isolate ponds, creeks or connecting channels without assessing effects on the species and downstream habitat.
  • Manage groundwater extraction, drawdown and discharge so that shallow flowing habitat is retained.
  • Prevent sediment and turbid runoff from entering clear-water habitat.
  • Maintain aquatic vegetation and gravel, cobble or boulder substrates.

Threats: Grazing, clearing and fragmentation

Habitat damage through grazing and lack of regeneration are documented threats. Most recorded populations were on private land, generally used for grazing. Clearing riparian vegetation or aquatic plants can remove cover, increase sediment and temperature stress, and break connections between suitable reaches, although the supplied documents do not quantify a road or clearing threshold.

  • Fence or otherwise protect sensitive creek and wetland margins from stock access where practicable.
  • Keep construction plant, spoil, access tracks and laydown areas away from aquatic vegetation and waterway beds.
  • Plan works to retain connected channels, vegetated margins and suitable flow paths.
  • Treat unconfirmed historical locations cautiously because the documented range has contracted with habitat degradation.

Threats: Introduced species and other pressures

Introduced fish competitors and predators are identified threats. Climate change is also identified as a major threat. The supplied documents do not identify a species-specific disease, road mortality pattern or fire response.

  • Prevent introduction or spread of non-native fish and aquatic organisms through clean-down and water transfer controls.
  • Do not transfer water, aquatic plants, sediment or captured fish between catchments unless authorised and managed under relevant biosecurity requirements.
  • Assess fire related risks through potential effects on riparian cover, erosion, sediment delivery and post-fire water quality rather than assuming a direct fire response.

Threats: Survey and construction precautions

Backpack electrofishing and trapping have similar detection rates and are effective for pygmy perch with low mortality rates when properly conducted. In South Australia, seine nets through littoral or submerged vegetation, fyke nets in more open water and bait traps in confined environments are reported as useful methods. Seine netting should avoid disturbing littoral or submerged vegetation.

  • Define the project area and all areas that could be affected indirectly, including downstream areas, before survey design.
  • Use a combination of suitable methods where access, depth, flow and vegetation allow.
  • Minimise handling and habitat disturbance during surveys and construction monitoring.

Survey methodology: 1. Confirm habitat and survey extent

Survey this species where works may affect clear, cool freshwater streams, ponds, wetlands or connecting channels in south-western Victoria and south-eastern South Australia. Use a qualified freshwater fish ecologist, because the species is small, sensitive to handling and difficult to detect in degraded or historically occupied habitat.

Map the full project area and any downstream or indirectly affected waterways, wetlands, ponds and connecting channels before selecting survey sites.

Prioritise shallow, clear freshwater with moderate to high flow, submerged or emergent aquatic vegetation, gravel, cobble or boulder substrate and little silt.

Include slightly brackish water, detritus-rich habitat at Ewens Ponds, and faster-flowing channels linking ponds where these occur.

Assess whether the site is used for breeding, shelter, feeding or movement, and compare current habitat with historical records because the species' range has contracted.

Known Australian range: Glenelg River system in south-western Victoria, and the Ewens Ponds, Piccaninnie Ponds and Eight-Mile Creek systems in south-eastern South Australia.

Preferred habitat: Relatively shallow, clear freshwater streams with moderate to high flow and abundant submerged or emergent aquatic vegetation.

Typical substrate: Gravel, cobble or boulder with little silt; large amounts of detritus occur at Ewens Ponds.

Survey methodology: 2. Seine-net sampling

Use a small, two-person seine with 2 to 5 mm mesh through littoral or submerged vegetation in suitable shallow habitat.

Work carefully around aquatic vegetation and avoid uprooting or otherwise damaging it.

Use seine sampling as a primary method in South Australian habitat where access and water depth allow it.

Remove captured fish with a dip net and place them directly into a container of site water while the net is being cleared.

Mesh size: 2 to 5 mm.

Best indicated habitat: Littoral or submerged vegetation, especially in South Australia.

Survey methodology: 3. Fyke nets and bait traps

Use fyke nets in more open water environments where seine sampling is unsuitable.

Use collapsible bait traps with approximately 3 mm mesh in confined environments or where the method is better suited to access and habitat.

Set bait traps for 30 to 60 minutes and check them thoroughly for fish.

Keep all captured fish in water for the minimum time possible and release them at the capture site unless an approved fish-management plan authorises another action.

Bait-trap mesh: Approximately 3 mm.

Bait-trap set time: 30 to 60 minutes.

Survey methodology: 4. Backpack electrofishing and dip-netting

Use backpack electrofishing in wadeable shallow streams, riffles, wetlands and lake margins, following the Australian Code of Practice and the equipment operator's safety requirements.

Combine backpack electrofishing with a fine-mesh seine and attached bag downstream of a riffle or rapid, or use a dip-net operator downstream to collect missed fish.

Combine electrofishing with trapping and dip-netting where this improves detection and remains safe for the fish and operator.

Do not use boat-based electrofishing as the default method for this species group, because the guideline states that it is generally unsuitable for most members of the group.

Suitable electrofishing habitat: Wadeable still water, shallow flowing streams and riffles.

Handling condition: Use wet hands, keep contact to a minimum and hold fish in a container of water when they are out of their habitat.

Survey methodology: 5. Timing, conditions and detection limits

Plan Victorian sampling between December and April where practicable, when water flows are lower and fish are more likely to be collected under the general threatened-fish guidance.

Record water temperature, pH, flow, water clarity, vegetation, substrate, depth and weather at each site so that non-detection can be interpreted against habitat conditions.

The species tolerates approximately 14 to 26 degrees Celsius and pH 6.8 to 7.5 in the wild, but these values are habitat information rather than a substitute for site assessment.

Avoid unnecessary disturbance during spring to early summer spawning and do not treat a single negative survey as proof of absence in historically occupied habitat.

The best time of day for sampling is not known for this species.

Wild temperature range reported: 14 to 26 degrees Celsius.

Wild pH range reported: 6.8 to 7.5.

Reported spawning period: Spring to early summer.

Best time of day: Unknown.

Survey methodology: Minimum effort and reporting

  • Use a combination of methods suited to water depth, flow, vegetation, access and salinity rather than relying on one method.
  • Document the length or area sampled, number and type of nets or traps, trap set times, electrofishing duration, personnel, equipment settings, weather and habitat conditions.
  • Record every capture, release, injury, mortality and non-target capture, including photographs and precise coordinates where safe and permitted.
  • Have fish handling and electrofishing undertaken by appropriately trained and authorised personnel, with a freshwater fish ecologist supervising the program.
  • Submit confirmed records and relevant negative-survey information to the relevant Victorian or South Australian wildlife or biodiversity database, as applicable to the project location.
  • Report any proposed impact to this EPBC Act listed species through the project's environmental approvals process and retain the survey report with the project records.

Before habitat disturbance: Avoid and minimise

Treat occupied or suitable aquatic habitat as a project constraint before clearing, excavation, dewatering, crossings or changes to flow. Ewens pygmy perch has a very restricted range, and most recorded populations are outside reserves.

Redesign the works to retain shallow, clear, well-vegetated streams, pond margins, connecting channels, riffles, gravel, cobble and boulder beds.

Avoid wetland drainage, groundwater extraction, silt entry, loss of aquatic vegetation, grazing damage and changes to natural flow.

Retain connectivity between ponds, streams and other occupied or suitable habitat, including downstream areas that could be affected by changed flow or water quality.

Keep machinery, stockpiles, access tracks, fuels and concrete washout away from waterways and wetland margins.

Do not remove aquatic vegetation, logs or accumulated cover from potential habitat unless the approved method statement requires it and a fish ecologist has assessed the action.

Population security: The recovery plan recorded 20 locations, with only Ewen's Ponds and Piccaninnie Ponds populations occurring in some form of reserve; the other 18 were on private land.

Before habitat disturbance: Approvals and work planning

Check whether the action requires assessment or referral under the EPBC Act because Ewens pygmy perch is nationally listed as Vulnerable.

Check Victorian or South Australian threatened-species, fisheries, waterway, dewatering, fish relocation and capture requirements before work starts.

Prepare a fauna and aquatic-habitat management plan that identifies known and potential habitat, survey results, exclusion areas, dewatering controls, fish rescue arrangements and stop-work triggers.

Stage works so that disturbance to breeding habitat is avoided during spring to early summer where practicable.

Obtain advice from the relevant state authority and a qualified fish ecologist before planning any relocation, salvage or release.

Australian Government status: EPBC Act Vulnerable.

Victoria status: Endangered under the state assessment cited in the recovery plan.

South Australia status: Protected under the Fisheries Act 1982 and listed as Endangered in the cited draft threatened-species schedules.

Before habitat disturbance: Site preparation

Complete a pre-clearance aquatic survey in all waterways, wetlands, ponds and channels that may be disturbed or dewatered.

Mark no-go habitat, aquatic vegetation, wetland margins, retained channels and vehicle exclusion areas before machinery enters the site.

Install exclusion fencing or equivalent controls where they can prevent entry by machinery, vehicles, stock or people without blocking fish movement or causing bank damage.

Brief the fauna spotter catcher, machine operators, supervisors and aquatic fish team on the species' appearance, habitat, handling limits and stop-work procedure.

Confirm clean equipment and biosecurity controls before moving machinery or sampling equipment between catchments.

During habitat disturbance: Daily controls and supervision

Use a stop, assess and control approach whenever works enter or affect aquatic habitat. A terrestrial fauna spotter catcher must not be treated as a substitute for an authorised freshwater fish ecologist during capture, dewatering or release activities.

Inspect exclusion fencing, sediment controls, bypasses, pumps, screens and retained habitat before work starts each day and after heavy rain or flow changes.

Keep machinery out of retained waterways and wetland margins unless the approved method specifically requires access and the fish ecologist is present.

Prevent sediment, fuel, concrete, contaminated water and spoil from entering occupied or suitable habitat.

Use low-flow or staged dewatering methods where dewatering is approved, and inspect isolated pools and wet areas before they are disturbed.

The fauna spotter catcher should maintain visual contact with the work area, communicate directly with the operator and stop the machine when an animal, fish rescue issue or unplanned habitat impact is identified.

During habitat disturbance: Fish handling and rescue

Stop work and notify the site supervisor and fish ecologist if an Ewens pygmy perch is seen, captured, stranded or found in an isolated pool.

Only trained and authorised personnel should capture, identify, handle or relocate the fish.

Use wet hands, minimise contact, keep the fish in site water and return it to suitable nearby retained habitat only where the approved plan and relevant authority allow that action.

Do not hold the fish out of water longer than necessary, and do not mix fish from different catchments or release fish into habitat that has not been approved.

Take photographs and record the location, habitat, method, number, condition, action taken and final release or treatment location.

Handling sensitivity: The species group is sensitive and easily stressed, and scales are easily lost during handling.

Diet: Aquatic insects and benthic microcrustaceans.

During habitat disturbance: Habitat feature controls

Protect submerged and emergent aquatic vegetation, shallow flowing channels, riffles, gravel, cobble, boulder and woody cover from unnecessary disturbance.

Do not treat logs, rocks or aquatic debris as disposable spoil where they provide cover or influence flow in retained habitat.

Maintain water quality, oxygenation, flow and connectivity during crossings, pumping and temporary diversions.

Do not assume that a dry or isolated channel is unoccupied, because the species' historical distribution has contracted and detection can be difficult.

Manage terrestrial hollow-bearing trees, logs, rocks and burrows under the project's general fauna plan, but prioritise aquatic habitat controls for this fish.

During habitat disturbance: Stop-work triggers and incident response

Stop the relevant activity if the species is found, fish are stranded, a pump or screen is injuring fish, sediment enters retained habitat, or approved flow and water-quality controls fail.

Stop work if the disturbance footprint extends into mapped habitat or if machinery damages aquatic vegetation, banks, riffles or connecting channels outside the approved area.

Move injured fish into clean site water and arrange prompt assessment by an aquatic wildlife veterinarian, wildlife carer or other authorised wildlife professional.

Report mortality, injury, unapproved capture, unplanned habitat damage, pollution or failed controls to the project environmental officer and the relevant authority under the approval conditions.

Resume work only after the fish ecologist and project environmental officer confirm that the cause has been controlled and the approval requirements are met.

After habitat disturbance: Post-clearance and construction checks

Do not close out the aquatic work area when machinery leaves. Confirm that retained habitat, water quality and fish movement have been restored, then monitor the site for impacts that may appear after construction.

Complete a final inspection of all disturbed waterways, isolated pools, pond margins, connecting channels and downstream areas before removing the fish rescue team and aquatic controls.

Check for stranded or trapped fish, damaged aquatic vegetation, blocked movement paths, bank collapse, new silt deposits, changed flow and poor water clarity.

Remove temporary structures, spoil and waste without disturbing retained habitat or leaving barriers to fish movement.

Keep sediment, pollution, dewatering and access controls in place until banks and water quality are stable and the project environmental officer signs them off.

After habitat disturbance: Monitoring and reporting

Monitor occupied or suitable retained habitat after works using the same sites and methods where practicable so that results can be compared with pre-work conditions.

Record water temperature, pH, flow, clarity, aquatic vegetation, substrate, fish detections, injuries, mortalities and any introduced fish or predator observations.

Report confirmed records and incidents to the relevant state wildlife database or authority, and meet all EPBC Act, state approval and project reporting conditions.

Update the site management plan if monitoring identifies loss of flow, vegetation, connectivity or water quality.

Comparison basis: Use pre-work survey sites and methods where practicable.

After habitat disturbance: Offsets and residual impacts

Apply the project's EPBC Act and state approval requirements if impacts remain after avoidance and mitigation.

Use the recovery plan's identified threats, including wetland drainage, groundwater extraction, grazing damage, lack of regeneration, climate change and introduced fish, when assessing residual risk.

Do not describe an offset or habitat action as replacing retained occupied habitat unless it has been approved by the relevant authority.

Rehabilitation actions: Restore aquatic habitat

Rehabilitation should restore the clear, cool, connected freshwater habitat used by Ewens pygmy perch. Focus on flow, aquatic vegetation, stable substrates, water quality and protection from introduced fish and catchment disturbance.

Re-establish shallow channels with moderate to high flow where those features were present before the works.

Replant or allow recovery of submerged and emergent native aquatic vegetation along retained stream and pond margins.

Reinstate stable gravel, cobble and boulder habitat where it was removed, while preventing fine sediment from covering the substrate.

Retain or replace suitable woody debris and accumulated cover only where the fish ecologist confirms that it will not block fish passage or cause erosion.

Maintain clear, well-oxygenated water and prevent polluted runoff, excessive turbidity and groundwater changes from reaching the rehabilitated habitat.

Habitat association: The species is strongly associated with submerged and emergent aquatic vegetation and prefers clear water.

Substrate association: Gravel, cobble or boulder is preferred in most reported habitat, with detritus important at Ewens Ponds.

Rehabilitation actions: Catchment and threat management

Control weeds and grazing pressure around rehabilitated stream and wetland margins so native riparian and aquatic vegetation can regenerate.

Prevent introduced fish from entering retained or restored habitat through construction ponds, water transfers and connected drainage.

Manage erosion, sediment and stormwater at the source rather than relying only on treatment at the waterway edge.

Protect groundwater-dependent ponds and channels from project-related extraction or drawdown.

Consider fire management for adjacent vegetation and wetland margins, but obtain advice before planned burning near aquatic habitat.

Rehabilitation actions: Rehabilitation monitoring and success measures

Monitor rehabilitated sites through the establishment period and compare them with pre-work records and nearby retained habitat.

Measure whether flow, water clarity, aquatic vegetation, substrate, connectivity and bank stability are returning to the agreed reference condition.

Use repeat fish surveys with suitable combinations of seine nets, fyke nets, bait traps, backpack electrofishing and dip-netting where safe and authorised.

Treat detection of Ewens pygmy perch as one outcome measure, not the only measure, because the species can be difficult to detect and historical ranges have contracted.

Continue weed, grazing, sediment, water-quality and introduced-fish controls until the agreed habitat and fish-survey outcomes are met.

Detection limitation: A non-detection does not by itself demonstrate absence, particularly in historically occupied habitat.

Survey option for South Australia: Seine nets through littoral or submerged vegetation, fyke nets in more open water and bait traps in confined environments are indicated methods.

Sources