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Cave Gudgeon (Milyeringa veritas)

The Cave Gudgeon is a small, eyeless subterranean fish restricted to groundwater, caves, wells, sinkholes and anchialine systems in Western Australia. It is listed as Vulnerable under the EPBC Act and in Western Australia, so works that alter groundwater levels, salinity, water quality or access to cave and well habitats may affect it even when no fish are visible at the surface.

Conservation status

Commonwealth, EPBC Act 1999: Vulnerable.

Western Australia, Biodiversity Conservation Act 2016: Vulnerable.

Breeding season

Seasonal information is limited. The only indication of reproduction is the repeated observation of small fish from December to March, while movements within the water column occur throughout the year and can vary between years.

Months are January to December. The seasonal pattern is indicative only because reproduction has not been directly observed and abundance varies between years.

  • Breeding: Breeding behaviour and spawning sites are unknown. Small fish have been recorded from December to March, suggesting possible seasonal breeding.
  • Young: Small individuals less than 18 mm standard length have been observed from December to March in several years. The period of dependence is unknown.
  • Movement within groundwater: Fish move widely through the water column and may occur at different depths between years. No seasonal movement period has been established.
  • Highest clearing risk: Groundwater and karst habitat can be affected in any month by clearing, excavation, pumping or contamination. Apply heightened precaution from December to March because this is the only period associated with observations of very small fish.

Identification

The Cave Gudgeon is a small, pale subterranean fish. It is often seen hovering or swimming slowly in wells, sinkholes and cave pools, but its position in the water column can vary between years.

Adults and juveniles are generally white, pale pink or translucent. The fish lacks visible eyes and has a reduced, cave-adapted appearance. The brain may be visible through the braincase, scales are reduced on the body and absent from the head, and sensory papillae on the head and body help detect surroundings and prey.

The species is small. The SPRAT profile gives a maximum of 4.5 cm, while published measurements include fish from 5 to 57 mm standard length. No reliable field weight information was provided.

  • Look for a pale, eyeless fish with a relatively slow, hovering swimming style.
  • Check the full water column, not only the bottom or edges, because fish have been observed from the surface to 33 m depth.
  • Use photographs and expert confirmation where possible, particularly for records from groundwater bores or poorly accessible caves.

Identification: Separating similar species

The main native species likely to be confused with the Cave Gudgeon in these subterranean waters is the Blind Cave Eel, Ophisternon candidum. Both are eyeless and may occur in the same cave systems, but the gudgeon has a compact fish-like body and gudgeon swimming behaviour, while the eel has an elongated eel-like body and different swimming behaviour.

The threatened fish survey guidelines state that accurate identification is unlikely to be difficult because the two species are geographically isolated from related taxa and differ clearly in body form. A feral tropical aquarium fish has also been observed in one cave, so unusual records should be documented and referred to a qualified fish specialist.

  • Do not identify a pale fish from colour alone.
  • Record body shape, swimming behaviour, approximate size, water depth and the cave, well or bore location.
  • Do not collect the fish unless authorised, because the species is fully protected.

Identification: Field signs and survey observations

There are no known terrestrial field signs such as tracks, scats, nests, calls, sloughs or eyeshine. Detection depends on observing fish in water or using an approved aquatic survey method.

Fish may hover near the surface, perch on rock ledges, investigate disturbance, move behind ledges and other obstacles, or forage through the water column. They have sometimes been observed in sunlight, and may be easier to see from the surface on a sunny day.

  • Inspect wells and sinkholes from above during daylight and, where safe and authorised, use snorkelling or underwater observation.
  • Night observation with headlamps from above wells or holes can also detect the species.
  • Use specialist caving personnel where entry is needed because many caves are vertical, unstable or contain dangerous concentrations of carbon dioxide.
  • Treat a non-detection cautiously because abundance and vertical distribution vary between years.

Distribution: National range

The Cave Gudgeon is an Australian endemic known from Western Australia. Its confirmed range is concentrated in the Cape Range coastal plain and Barrow Island, with possible but unconfirmed occurrence in mainland aquifers opposite Barrow Island.

The species is known only from Western Australia. On the Cape Range Peninsula, its known range extends along the coastal plain from the Exmouth area to Javis Well, a distance of about 136 km along the coast. Records occur on both the western and eastern sides of the peninsula.

It is also known from Barrow Island, about 160 km northeast of North West Cape. The species may occur in the lower Robe River and Fortescue River aquifers on the mainland opposite Barrow Island, but this remains a possibility rather than a confirmed part of the known range.

  • Relevant regional setting: Cape Range Peninsula, North West Cape and Barrow Island.
  • Relevant broad bioregional context: the Cape Range coastal plain and associated Pilbara coastal groundwater systems.
  • No records were provided from any Australian state or territory other than Western Australia.

Distribution: Known sites and subpopulations

Recorded Cape Range sites include Kudumurra Well, Milyering Well, Five Mile Well, Homestead Well, New Yardie Well, Pilgramuna Well, Tantabiddi Well, small sinkholes south of Tantabiddi Creek, Javis Well, Kubura Well and Mowbowra Well. Records also include other wells, caves and sinkholes across the coastal plain.

Genetic work identified substantial population structuring across the peninsula, including a broad western and eastern grouping. This indicates restricted gene flow between some groundwater populations, which should be considered when assessing disturbance to an individual cave, well or aquifer unit.

  • Known populations may be isolated from one another by groundwater and geological conditions.
  • Barrow Island records include a deep groundwater bore and are not necessarily connected to surface waters.
  • The SPRAT distribution map may include Barrow Island records affected by a changed taxonomic concept, so site-specific advice should be checked before relying on a mapped range.

Distribution: Population size and trend

A formal range-wide population estimate is not available. Counts at individual caves vary from a few fish to around 100, and a minimum population estimate at Kubura Well was 48 fish in June 1993 and 43 fish in July 1993.

The species survey guidelines report that distribution and abundance differ between years. Historical observers also considered numbers at some wells to be lower than formerly, but the available information is insufficient to establish a range-wide trend.

Recorded number at caves: A few to around 100 fish at individual sites.

Kubura Well estimate: 48 fish in June 1993 and 43 fish in July 1993, minimum estimates.

Known sites: At least 25 sites were reported in the SPRAT biological profile.

Range-wide trend: Unknown; abundance and distribution vary between years.

Habitat: Underground karst habitat

The Cave Gudgeon occupies underground karst waters rather than ordinary surface streams or ponds. Its habitat includes freshwater caves, sinkholes, wells, bores and anchialine groundwater systems with a wide range of salinity and oxygen conditions.

The species is restricted to groundwater beneath the Cape Range coastal plain and associated karst systems, including Tertiary limestone caves and flooded conduits. It has been recorded within 150 m of the coast and up to 4.3 km inland.

It occurs in freshwater caves and in anchialine systems where fresh or brackish groundwater overlies seawater and is affected by marine tides. Recorded water conditions range from fresh water to salinities of about 34 g per litre total dissolved solids.

  • Assess flooded caves, sinkholes, wells, bores and groundwater conduits as potential habitat.
  • Include groundwater and connected subterranean habitat in the impact area, not only the visible surface opening.
  • Do not assume that saline or tidally influenced groundwater is unsuitable.

Habitat: Water and physical conditions

The fish has been sampled at water depths up to 33 m and from bores where the water table was up to about 47 to 50 m below ground. It has been recorded in water temperatures from 27 to 30 degrees Celsius in May and August.

The species tolerates marked chemical variation, including hyperoxic surface water, suboxic water below density interfaces, saline water and areas near hydrogen sulphide and sulphur bacteria. The same cave may contain strongly stratified water masses.

  • Record groundwater level, temperature, salinity or conductivity, dissolved oxygen and visible stratification where safe and authorised.
  • Treat changes to the freshwater lens, saltwater interface, tidal influence or groundwater flow as potential habitat impacts.
  • Avoid disturbing sediments, ledges and water interfaces unnecessarily during inspection or construction.

Habitat: Surface setting

The source material does not identify a specific vegetation community required by the species. Some fish populations use surface-connected wells and sinkholes where terrestrial invertebrates enter the water, while other populations occur in groundwater remote from surface openings.

The surrounding climate is arid tropical, with episodic heavy rainfall and high evaporation. Surface clearing can therefore matter indirectly where it changes recharge, runoff, food inputs or access to a cave, well or sinkhole.

  • Map surface openings, drainage lines, recharge areas and groundwater infrastructure before clearing or excavation.
  • Retain and protect known cave, well and sinkhole openings from fill, sediment, rubbish and uncontrolled access.
  • Assess changes to rainfall recharge and surface water entry where works occur over or near karst limestone.

Foraging habitat: Diet

The Cave Gudgeon feeds opportunistically in the water column and near submerged surfaces. Food sources differ between sites and include both groundwater fauna and terrestrial animals that enter through surface openings.

Recorded food includes aquatic shrimps, other stygofauna, caddis and other aquatic larvae, flies, terrestrial isopods, cockroaches and ants. Gut contents from sampled fish included detrital matter and fly remains, while broader dietary work found a predominance of terrestrial prey at some surface-connected sites.

At sites without surface wells or rockholes, aquatic shrimps and other groundwater invertebrates are likely to provide a greater share of available food. Stable isotope evidence indicates that the species is a predator rather than relying substantially on detritus or algae.

  • Protect aquatic invertebrate communities in occupied caves, bores and sinkholes.
  • Prevent sediment, hydrocarbons, chemicals and other pollutants from entering surface openings or recharge areas.
  • Retain natural surface openings where they provide access for terrestrial prey, while preventing unauthorised access and contamination.

Foraging habitat: Foraging behaviour

The fish moves widely through the water column and may hover in mid-water or near the surface. It has also been observed foraging immediately above sediments and sulphur bacterial layers, and following an advancing tidal front through shallow anchialine conduits.

It can take prey while nearly stationary, using a sudden gulp. It may forage near the surface at wells and sinkholes, particularly at night, but the vertical position of fish can change markedly between years.

  • Inspect the full water column during surveys, including surface, mid-water, ledges and near-bottom areas.
  • Record water depth and position of fish, because a single observation may not represent the usual distribution at that site.
  • Avoid lighting, noise, sediment disturbance and water-quality changes that could alter feeding behaviour during surveys.

Foraging habitat: Foraging range

A home range or regular travel distance has not been established. Individuals may move widely through the water column within a cave, but movement between separate water masses or groundwater systems is not known.

Genetic differences between populations indicate that movement and gene flow between some sites are restricted, even though fish may move extensively within an occupied cave or groundwater body.

Breeding habitat: Known reproductive information

Very little is known about reproduction in the Cave Gudgeon. Small fish have been recorded in December to March, suggesting a possible breeding period, but the spawning site, eggs, parental care and development are not described in the available sources.

The breeding method is unknown. The species is difficult to observe in life because it occupies subterranean water, and no reliable description of spawning behaviour or egg deposition was provided.

Small individuals less than 18 mm standard length have been observed from December to March in several years. This may indicate a distinct breeding season, but annual or seasonal breeding has not been confirmed across the range.

Breeding season: Unknown; small fish have been recorded from December to March, suggesting possible seasonal breeding.

Eggs or clutch size: Not known.

Gestation or incubation: Not known.

Age at maturity: Not known.

Lifespan: Not known.

Smallest recorded fish: About 4.5 mm standard length in the SPRAT profile; published measurements include fish from 5 mm standard length.

  • Treat occupied caves, wells, sinkholes, bores and connected groundwater as potential breeding habitat because breeding locations have not been identified separately.
  • Do not drain, dewater, fill or chemically alter occupied groundwater habitat during any suspected recruitment period.
  • Refer unusual observations of eggs, larvae or very small fish to a fish specialist and record the exact site and water conditions.

Breeding habitat: Breeding habitat features

Specific breeding structures have not been identified. The best-supported approach is to protect the complete occupied groundwater system, including flooded chambers, rock ledges, conduits, sediments, water interfaces and surface-connected openings.

Because fish may occur in both fresh and anchialine waters and through depths to 33 m, breeding habitat should not be assumed to be limited to shallow freshwater pools.

  • Maintain groundwater levels, flow paths, salinity gradients and oxygen conditions at occupied sites.
  • Prevent sediment or construction material from entering cave pools, sinkholes, wells and bores.
  • Use the December to March period as a heightened precautionary period for disturbance near known habitat, while recognising that reproduction is not fully understood.

Sheltering habitat: Subterranean refuges

The Cave Gudgeon shelters within subterranean water bodies rather than using terrestrial dens, hollows or nests. It may remain suspended in the water, perch on rock ledges or move beneath ledges and behind obstacles when disturbed.

Known refuge habitat includes flooded caves, sinkholes, wells, bores and groundwater conduits in limestone. Fish have been recorded through the full water column of Bundera Sinkhole to 33 m and from groundwater where the water table is about 47 to 50 m below ground.

The species may hang almost motionless in the water or perch on rock ledges for long periods. When disturbed, it may swim to the bottom or move beneath ledges and behind obstacles.

Recorded cave depth: Fish observed to 33 m depth at Bundera Sinkhole.

Recorded groundwater depth: Water table up to about 47 to 50 m below ground at sampled bores.

  • Protect rock ledges, flooded chambers, sediment margins and vertical water zones within occupied sites.
  • Keep cave and sinkhole openings free of fill, concrete, waste and excessive surface runoff.
  • Do not assume that a section of cave is unused because no fish are visible during one inspection.

Sheltering habitat: Surface openings and access

Some populations are associated with wells, rockholes and sinkholes that allow terrestrial insects and other prey to enter the water. Other fish occur in groundwater remote from known surface openings.

Cave and sinkhole openings can be vertical, unstable and affected by dangerous carbon dioxide concentrations. Site access for surveys or works should therefore be managed by people with appropriate caving, confined-space and aquatic safety skills.

  • Fence or otherwise control access to hazardous openings without sealing or altering the groundwater connection.
  • Use qualified caving specialists where entry, roping or underwater work is proposed.
  • Include indirect effects from nearby excavation, blasting, pumping and altered drainage in the habitat assessment.

Threats: Groundwater abstraction and hydrology change

The main project risks are changes to the groundwater system and physical damage or contamination of caves, wells, sinkholes and recharge areas. The species can occupy very small, isolated populations, so impacts at one groundwater site may affect a distinct genetic group.

The Cape Range freshwater lens is vulnerable to saltwater upconing when groundwater is pumped, and seawater may migrate inland. Historic use of groundwater by pastoralists, Exmouth, military facilities and other users has affected subterranean water resources.

Construction dewatering, borefield expansion, pumping, drainage changes, excavation into limestone and altered recharge may change water levels, flow paths, salinity, tidal influence, oxygen conditions or chemical stratification.

  • Assess drawdown and recovery beyond the project footprint, including effects on connected caves, wells, sinkholes and bores.
  • Monitor groundwater level, salinity or conductivity, temperature and water quality before, during and after works where occupied habitat may be connected.
  • Avoid unplanned pumping or discharge into the freshwater lens and obtain the required approvals before altering groundwater.

Threats: Clearing, excavation and infrastructure

Surface clearing can damage or block cave and sinkhole openings, change recharge and runoff, and reduce the entry of terrestrial prey. Excavation and infrastructure may also intersect previously unknown karst voids or groundwater conduits.

Fragmentation is primarily a groundwater and karst connectivity issue for this species. Genetic evidence shows restricted gene flow between some populations, so damage to one site may not be readily offset by nearby habitat.

  • Survey for caves, sinkholes, wells, bores, karst depressions and recharge features before clearing or excavation.
  • Stop work and obtain specialist advice if a flooded void, fish or previously unknown groundwater connection is found.
  • Keep sediment, spoil, concrete washout, fuels and other pollutants away from karst openings and recharge areas.
  • Retain hydrological connections unless a specialist assessment demonstrates that they are not occupied or connected to occupied habitat.

Threats: Fire, roads and predators

The supplied sources do not identify fire, roads or predation as demonstrated major threats to the Cave Gudgeon. These pressures may still matter indirectly if they alter recharge, sediment delivery, access to openings, water quality or the supply of terrestrial prey.

The fish is itself a predator in the subterranean food web. The available sources do not identify a particular introduced predator as a confirmed threat, although a feral tropical aquarium fish was observed in one cave.

  • Prevent road drainage, fire suppression water, sediment and contaminated runoff from entering sinkholes, wells or recharge zones.
  • Do not introduce bait, aquarium fish or other aquatic animals into caves, bores or wells.
  • Assess any proposed firebreak, road, culvert or drainage work near karst openings for groundwater and sediment effects.

Threats: Disease and handling

The source material reports susceptibility to Saprolegnia fungus in freshwater in captivity. It does not establish the prevalence or field impact of disease in wild populations.

Handling, collection, equipment transfer and movement of water between sites could introduce pathogens or degrade water quality. The species is fully protected and normally should not be collected.

  • Use site-specific, clean equipment and prevent transfer of water or biological material between caves, wells and bores.
  • Avoid capture unless it is authorised under the relevant permits and undertaken by qualified specialists.
  • Report sick, dead or unusually behaving fish with photographs, location and water-quality observations.

Survey methodology: 1. Define the potential impact area

Survey Cave Gudgeon only where a project may affect the Cape Range coastal groundwater system, limestone caves, sinkholes, wells, bores or connected anchialine habitat. The species is subterranean, protected and difficult to detect from surface works alone, so surveys must be designed by an aquatic ecologist with cave and groundwater experience.

Map the project area and all places that may be affected indirectly, including groundwater drawdown, pumping, dewatering, changes to recharge, altered drainage, vibration, contamination and access to caves or sinkholes.

Include connected caves, wells, bores, rock holes and groundwater features in the assessment. The species has been recorded from sites within 150 metres of the coast and up to 4.3 kilometres inland, and from groundwater reached by bores up to 47 to 50 metres below the surface.

Treat the Cape Range Peninsula and Barrow Island as the known Australian range. Mainland aquifers near the lower Robe and Fortescue rivers are possible habitat, but occurrence there is unconfirmed.

Adult size: Usually up to about 4.5 to 5 centimetres, with recorded standard lengths from 5 to 57 millimetres.

Known range: Cape Range Peninsula, Western Australia, and Barrow Island.

Habitat depth: Surface openings to at least 33 metres in caves, and groundwater with the water table up to about 47 to 50 metres below ground.

  • Obtain current records from SPRAT, state databases, the Protected Matters Search Tool, local researchers and relevant land managers before finalising the survey design.
  • Record the limestone formation, depth to groundwater, salinity, tidal influence, water temperature, access points and any proposed change to groundwater levels or quality.

Survey methodology: 2. Daytime visual observation

Inspect wells, sinkholes, rock holes and accessible cave pools during daylight, preferably on a sunny day. The species has sometimes been observed swimming in sunlight, and daylight can improve observation from the surface.

Use a standardised visual search of the full visible water column, including the surface, ledges, walls and deeper water. Divers have observed fish through the full 33 metre depth of Bundera Sinkhole, but vertical distribution changes between years.

Where safe and authorised, snorkelling or diver observation can be used in suitable water bodies. Do not enter unstable caves or high carbon dioxide areas without a site-specific cave safety assessment and suitably qualified caving personnel.

Recommended conditions: A sunny day may assist surface observation.

Detection time: The blind gudgeon can generally be located in less than one hour at accessible occupied sites, although absence after one search is not evidence of absence.

Water column: Fish may occur from near the surface to at least 33 metres, with depth distribution varying between years.

  • Record the start and finish time, weather, water level, visibility, water temperature, salinity or conductivity, observer position and the depth searched.
  • Use photographs or video where possible because the fish is small, white to translucent, eyeless and may be confused with other subterranean fauna without a clear record.
  • Do not collect fish merely to confirm identification. The species is fully protected and normally does not need to be collected.

Survey methodology: 3. Night observation with headlamps

Search from above wells, sinkholes and other openings at night using headlamps. The species is often near the surface at wells and sinkholes at night and can be detected without entering the water.

Repeat the same search route and observation points used during the day so that results can be compared between visits. Record fish numbers, estimated size classes, depth and behaviour.

Do not use night access to unstable caves, vertical shafts or areas with dangerous carbon dioxide concentrations unless a specialist cave team has approved and controls the entry.

Night method: Headlamp observation from above wells or holes is an accepted detection method.

Search duration: The guideline indicates that the species is generally located in less than one hour at accessible sites.

  • Use a low disturbance approach and avoid repeated handling, chasing or bright light exposure that could alter fish behaviour.
  • If a fish is seen, record its position and take an image from a safe distance rather than attempting capture.
  • Treat a non-detection cautiously because abundance and distribution differ between years and the fish may occupy different depths or water masses.

Survey methodology: 4. Limited capture and groundwater investigation

Use capture only where it is necessary for a lawful survey, identification or scientific purpose, and only under the required permits. Historical observations indicate that a small dip net can attract fish when insects fall into the water, but the species is protected and routine collection is not required.

Where project impacts involve bores or groundwater, engage a subterranean fauna specialist to assess whether haul nets, traps, environmental DNA or other methods are appropriate. The supplied guidelines support visual observation for this species but do not provide a standard trap-night, transect or eDNA effort.

Measure groundwater conditions at representative sites because the fish occupies fresh, brackish and saline groundwater, with reported salinities up to 34 grams per litre total dissolved solids and temperatures of about 27 to 30 degrees Celsius in earlier records.

Reported habitat water temperature: About 27 to 30 degrees Celsius in May and August at sites described in the SPRAT profile.

Reported salinity range: Freshwater to about 34 grams per litre total dissolved solids.

Capture effort: No species-specific trap-night, transect or area standard is provided in the supplied documents.

  • Do not lower equipment, pumps or sampling gear into a cave, well or bore until the site has been checked for fish, water quality hazards, structural instability and approval requirements.
  • Decontaminate equipment between sites to avoid transferring pathogens, sediment, pollutants or non-native aquatic organisms.
  • Have a qualified aquatic ecologist identify any captured specimen, minimise handling time and return it to the capture location unless a permit directs otherwise.

Survey methodology: Minimum effort and reporting

  • Survey every accessible cave, sinkhole, well, rock hole and bore that could be affected directly or indirectly by the project, using both daytime visual observation and night headlamp observation where safe and authorised.
  • Search the full visible water column and repeat surveys where water level, visibility, groundwater chemistry or access conditions change materially.
  • Use a qualified aquatic ecologist and suitably qualified cave personnel for any entry, diving, night descent, groundwater sampling or capture work.
  • Report the site coordinates, habitat type, search method, search duration, date, time, weather, water conditions, depth searched, observers, photographs, fish observations and non-detections.
  • Submit confirmed records and suitable negative survey information to the relevant Western Australian wildlife or biodiversity database and to the Australian Government SPRAT record system where requested.
  • Keep records of all permits, approvals, risk assessments, decontamination, handling, injuries, mortalities and changes to groundwater levels or quality.

Before habitat disturbance: Avoid and minimise habitat impacts

Avoid disturbance to the groundwater and cave system first. A surface clearing footprint can affect this species through groundwater pumping, recharge changes, contamination or damage to access points and connected karst habitat.

Redesign the project to retain limestone caves, sinkholes, wells, rock holes, bores and connected groundwater features wherever practicable.

Avoid groundwater extraction, dewatering, drainage interception and discharge changes that could lower the freshwater lens, increase salinity or alter tidal groundwater exchange.

Retain natural recharge areas and prevent sediment, hydrocarbons, concrete wash water, chemicals and other contaminants from entering sinkholes, caves, bores or porous limestone.

Maintain connections between occupied or potentially occupied groundwater bodies. The species has genetically structured populations and restricted gene flow on the Cape Range Peninsula.

  • Set project exclusion areas around every known or potential karst opening and identify the required separation distances in the project environmental management plan after specialist hydrogeological advice.
  • Do not fill, cap, seal, drain or modify a cave, sinkhole, well or bore until its ecological value and connection to groundwater have been assessed.
  • Use bunding, spill kits, sediment controls and clean water diversions before earthworks begin.

Before habitat disturbance: Check approvals and plan the works

The Cave Gudgeon is listed as Vulnerable under the EPBC Act and in Western Australia under the Biodiversity Conservation Act 2016. Obtain project-specific legal advice before works begin.

Refer the action to the Australian Government if it may have a significant impact on the species or its habitat. Obtain any Western Australian permits required for taking, handling, disturbing or relocating protected fauna and for cave, groundwater or diving work.

Prepare a fauna and groundwater management plan that identifies no-go areas, survey results, dewatering controls, water quality limits, stop-work triggers, authorised personnel, incident contacts and reporting requirements.

Stage works so that high-risk activities, including drilling, blasting, pumping, trenching and dewatering, occur only after baseline groundwater and fauna information has been collected.

EPBC status: Vulnerable, effective from 16 July 2000.

Western Australian status: Vulnerable under the Biodiversity Conservation Act 2016 list cited in SPRAT.

Recovery plan: No adopted or made recovery plan is identified in SPRAT.

  • Confirm whether the project affects the listed concept of Milyeringa veritas, noting that the SPRAT distribution map may not match the current taxonomic concept around Barrow Island.
  • Nominate an aquatic ecologist, hydrogeologist, cave safety lead and authorised fauna handler before mobilisation.
  • Brief all workers that the species is a small, protected subterranean fish and that a surface opening may connect to occupied groundwater habitat.

Before habitat disturbance: Prepare and mark the site

Complete the pre-clearance aquatic and karst survey before clearing, drilling, pumping or altering a water body.

Mark all known and potential caves, sinkholes, wells, bores, groundwater access points and exclusion areas on plans and on the ground where this can be done without entering unsafe areas.

Install exclusion fencing or equivalent barriers around openings and retained habitat where they can prevent vehicle access, spoil placement, sediment entry or accidental filling.

Confirm that machinery access, laydown areas, spoil stockpiles and refuelling areas are outside recharge areas and karst openings.

  • Use a pre-start inspection each day to confirm that barriers, spill controls, covers and signage remain in place.
  • Do not rely on exclusion fencing alone where groundwater or contaminant pathways can bypass the surface boundary.
  • Record baseline water level, temperature, conductivity or salinity, turbidity and dissolved oxygen at representative sites where the project could change groundwater conditions.

During habitat disturbance: Daily controls and machinery coordination

The fauna spotter catcher must work with the aquatic ecologist and machinery supervisors. The main risks are not ordinary terrestrial encounters but changes to groundwater, physical damage to karst openings and pollution of subterranean water.

Inspect exclusion areas, cave and sinkhole barriers, sediment controls, bunds, spill kits, bore controls and water monitoring points before work starts each day.

Keep machinery, spoil, concrete, fuels and chemicals away from caves, sinkholes, wells, bores, rock holes and drainage lines leading to them.

Require the operator to stop before excavating, drilling, trenching, blasting, pumping or placing material within the approved exclusion area or near an unassessed opening.

Use a spotter and operator communication method that allows an immediate stop, including radio contact and a clearly understood stop signal.

  • Keep a fauna spotter catcher or nominated environmental representative available for all works that may expose, block, drain, contaminate or vibrate a subterranean water feature.
  • Do not allow workers to enter caves, shafts, wells or sinkholes to retrieve fauna unless the entry is approved, risk assessed and led by qualified cave personnel.
  • Prevent washdown water and dirty water from entering karst openings or groundwater recharge areas.

During habitat disturbance: If a Cave Gudgeon is found

Stop the activity that may affect the animal or its water body and keep machinery, people and lights away from the observation point.

Notify the aquatic ecologist, project environmental officer and relevant approval contact. Confirm the species from photographs or video where possible.

Only a person authorised under the relevant permit may capture, handle or relocate the fish. Do not net or move it as a routine fauna spotter catcher action.

If relocation is approved, move the fish only to nearby retained habitat with matching water chemistry and a confirmed hydrological connection, under the direction of the aquatic ecologist.

  • Do not place the fish in a bucket, surface drain or unrelated water body.
  • Do not transport the fish between caves, wells, groundwater systems or project areas without written approval and specialist direction.
  • If the fish is injured, contact the authorised aquatic fauna specialist and an appropriate aquatic wildlife rehabilitator or veterinarian, recognising that ordinary wildlife carers may not be equipped for subterranean fish.

During habitat disturbance: Stop-work triggers and records

Stop work immediately if a Cave Gudgeon is observed, if an unrecorded cave, sinkhole or groundwater opening is exposed, or if pumping, excavation or contamination could affect a connected water body.

Stop and contain the incident if there is a spill, sediment discharge, concrete discharge, unexpected salinity change, rapid water-level change, fish mortality or loss of an exclusion barrier.

Resume only after the aquatic ecologist and project environmental officer have assessed the risk, implemented controls and confirmed that the approval conditions allow work to continue.

  • Record the date, time, coordinates, activity, machinery, personnel, water conditions, fish observations, photographs, actions taken, person authorising the response and any mortality or injury.
  • Record groundwater levels and water quality before, during and after dewatering or other high-risk work at the frequency specified in the approved management plan.
  • Report any listed fauna incident, unauthorised handling, mortality, pollution event or approval breach to the relevant regulator within the required timeframe.

After habitat disturbance: Inspect and monitor retained habitat

Post-work checks must confirm that the project has not changed access to habitat or the groundwater conditions on which the species depends. Monitoring should continue for as long as project approvals and hydrogeological risk assessment require.

Inspect all retained caves, sinkholes, wells, bores and other affected groundwater access points after clearing, construction, drilling, dewatering or reinstatement.

Repeat daytime and night visual searches at occupied or high-risk sites using the same observation points and recording method used for baseline surveys.

Monitor groundwater level, temperature, conductivity or salinity, turbidity and other project-specific water quality indicators at representative sites.

Compare post-work results with baseline records and investigate changes in fish presence, abundance, depth distribution, water chemistry or access conditions.

  • Keep barriers, covers, sediment controls and contamination controls in place until the environmental officer confirms that the risk has ended.
  • Inspect after heavy rainfall, flooding, pumping changes, spills, equipment failure or other events that could alter recharge or groundwater chemistry.
  • Use a qualified aquatic ecologist to interpret non-detections because the species distribution and abundance can change between years.

After habitat disturbance: Report outcomes and manage residual impacts

Provide the regulator and approval holders with survey results, monitoring data, incidents, photographs, water quality records, corrective actions and confirmation that controls were maintained.

Submit confirmed species records and relevant monitoring records to the relevant Western Australian biodiversity database and update the Australian Government project record where required.

If the project has caused an unavoidable residual impact, apply the approved EPBC and Western Australian requirements for offsets or other conservation measures. Do not treat an offset as a substitute for avoiding groundwater or cave damage.

  • Close out every stop-work event with a written finding, control measure, responsible person and verification date.
  • Retain the fauna and groundwater records with the project environmental file for the period required by the approval or management system.
  • Review the management plan if monitoring detects a change in groundwater level, salinity, contamination, fish presence or access to habitat.

Rehabilitation actions: Restore karst and groundwater function

Rehabilitation must restore karst and groundwater function rather than focus on terrestrial planting. The supplied documents do not identify particular plant species, nest boxes, logs or rocks as Cave Gudgeon habitat features.

Remove temporary fill, spoil, barriers and infrastructure from areas that must remain open for approved groundwater or cave function, unless a qualified hydrogeologist confirms that removal would cause greater harm.

Reinstate natural drainage and recharge pathways without directing dirty water into caves, sinkholes, wells or bores.

Keep cave openings, sinkholes and groundwater access points stable, safe and free of rubbish, sediment, weeds, fuels and construction material.

Do not seal or cap a groundwater opening as rehabilitation without first assessing whether it provides habitat access or hydrological connection.

  • Use clean, compatible materials and methods approved by a karst and groundwater specialist where an opening or aquifer has been damaged.
  • Prevent erosion and sediment movement from the rehabilitated area into karst openings.
  • Do not introduce fish, invertebrates, water, soil or plant material from other catchments into the subterranean system.

Rehabilitation actions: Manage water quality and surrounding land

Maintain stable groundwater levels and water chemistry within the project-specific limits set by the hydrogeological assessment and approval.

Control weeds, sediment, pollutants and feral or introduced aquatic organisms around recharge areas and access points.

Use locally appropriate native vegetation only where surface rehabilitation is required to control erosion or restore recharge conditions. The supplied species sources do not identify a particular planting list for Cave Gudgeon habitat.

Manage fire, vehicle access and future maintenance so that they do not damage limestone openings, expose contamination pathways or alter recharge.

  • Do not create artificial ponds or wetlands as a substitute for the species' groundwater habitat.
  • Do not install nest boxes or add logs and rocks as a Cave Gudgeon measure because the species is restricted to subterranean waters and the supplied documents do not identify those features as habitat requirements.
  • Inspect rehabilitated areas after rainfall and construction maintenance, then repair erosion or failed sediment controls promptly.

Rehabilitation actions: Measure rehabilitation success

Set success measures for retained and rehabilitated groundwater features, including stable access, no project-related contamination, no unacceptable change in groundwater level or salinity, functioning recharge pathways and compliance with approved monitoring limits.

Repeat visual surveys at relevant caves, wells, sinkholes and bores using consistent daytime and night methods. Record fish detections, numbers, depth, water conditions and search effort.

Continue monitoring until the aquatic ecologist and regulator agree that groundwater conditions and habitat controls are stable.

  • Compare results with baseline data and investigate any sustained decline in detections, change in depth distribution or change in water chemistry.
  • Record maintenance inspections, corrective actions, monitoring results and final sign-off in the project environmental report.
  • Share confirmed records with the relevant Western Australian wildlife database and other approved biodiversity repositories.

Sources