Fauna Spotters logo

Blind Cave Eel (Ophisternon candidum)

The Blind Cave Eel is a white, eyeless, eel-like fish that lives in groundwater, caves, wells and some permanent river pools in Western Australia. Works that disturb aquifers, surface water, recharge areas or cave habitat may affect it. It is listed as Vulnerable under both the Commonwealth EPBC Act and Western Australian legislation.

Conservation status

Commonwealth, EPBC Act 1999: Vulnerable.

Western Australia, Biodiversity Conservation Act 2016: Vulnerable.

Breeding season

The Blind Cave Eel is very poorly known, and no breeding months have been established in Australia. It occupies groundwater, caves, fissures, wells and some permanent surface pools, so activity and disturbance risk should be treated as year-round across Western Australia.

Breeding mode: Not recorded.

Breeding place: A male reportedly builds and guards a nest or burrow. The location and structure of breeding sites are not established.

Breeding timing: Not recorded.

Clutch or litter size: Not recorded.

Incubation or development period: Not recorded.

Age at maturity: Not recorded.

Breeding frequency: Not recorded.

Records and detectability can vary between years and regions, and a lack of sightings does not demonstrate absence because the species is difficult to survey in inaccessible subterranean habitat.

  • Documented breeding season: No month or seasonal breeding pattern has been established, so the species should not be assumed to have a low-risk breeding period.
  • Subterranean and pool activity: The Blind Cave Eel may be active throughout the year in groundwater, caves, fissures, wells and permanent pools, with individuals usually near the bottom or in soft sediment.
  • Feeding in cave and groundwater habitat: Feeding is associated with bottom sediments and cave crustaceans, and no seasonal feeding period has been documented.
  • Surface pool and groundwater presence: Records from groundwater, wells and Robe River surface pools indicate that the species can occupy connected subterranean and surface-water habitats year-round.
  • Highest clearing risk: Treat clearing, excavation, dewatering, contamination and hydrological change as potential risks in every month because breeding timing and refuge use are unknown.

Identification: Appearance and size

The Blind Cave Eel is a rare, subterranean fish. It can be difficult to detect, even where suitable habitat is present, so identification and survey work should be handled carefully.

The body is long, slender, round and eel-like. Adults can grow to about 40 cm long.

The fish is usually white, pink or otherwise unpigmented. It has no visible eyes, no scales and no fins apart from a thin, rayless membrane near the tail tip.

  • Large mouth with thick lips and strong teeth.
  • Four pairs of crescent-shaped gills with long horizontal openings.
  • A lateral line extends along much of the body.
  • The species is often found close to the bottom of the water column.

Identification: Calls and similar species

No call or echolocation behaviour is known for this fish. The Blind Cave Eel is not expected to be confused with the Blind Gudgeon, which has a different body form and swimming behaviour.

Other one-gilled eels occur in Australian fresh and brackish waters, but the Blind Cave Eel is the listed subterranean species in this group.

Identification: Field signs and handling

There are no reliable surface signs such as calls, droppings, nests, whitewash or odour. A live fish, a clear image, or environmental DNA result is needed for a confident record.

Do not enter unstable or carbon dioxide rich caves without suitably qualified caving personnel. Collection may require permits, animal ethics approval and approval under relevant Commonwealth and Western Australian laws.

  • Treat any white or eyeless eel-like fish from a bore, well, cave, sinkhole, groundwater pool or permanent river pool as a potential Blind Cave Eel.
  • Keep handling time short and avoid transferring water, sediment or equipment between sites.
  • Record the exact location, waterbody type, depth where known, salinity, water level and surrounding works.

Distribution: State and regional range

The Blind Cave Eel is endemic to Western Australia. Records are scattered and the known range has expanded as bores, surface pools and other groundwater habitats have been surveyed.

The species is known from Western Australia only. The main known areas are Cape Range, Barrow Island and the Pilbara, including the Robe River catchment.

Cape Range records include caves and artificial wells on both sides of the range. At least 11 Cape Range localities have been reported, although not all remain accessible or extant.

  • Cape Range Peninsula, including the Exmouth area and the Cape Range coastal plain.
  • Barrow Island karst aquifers and artificial wells.
  • Bungaroo Creek, Jimmawurrada Creek and the Robe River system in the Pilbara.
  • Permanent and semi permanent pools and shallow alluvial groundwater in the Robe River catchment.

Distribution: Known range in the Pilbara

The Robe River catchment population has been recorded from more than 15 sites, including bores and surface pools. Records extend along more than 100 km of the Robe River system, with potential for further records inland and towards the coast.

The mapped habitat extent in the Robe River catchment was conservatively estimated at 19,175 hectares. This should not be treated as the full species range.

Notable record: A specimen was first recorded from Bungaroo Creek in 2009.

Survey expansion: Later surveys detected the species at additional bores and surface pools in the Robe River catchment.

Distribution: Implications for site assessment

An absence of records does not demonstrate absence. Groundwater habitat may extend beneath areas with no caves, wells or previous survey access.

Before clearing or excavation, check regional records and identify connections between proposed works, aquifers, river pools, caves, sinkholes and groundwater recharge areas.

  • Consider both known habitat and connected potential habitat.
  • Use qualified subterranean fauna specialists where groundwater or karst systems may be affected.
  • Treat new records from bores, pools or cave systems as significant and report them through the relevant approval pathway.

Habitat: Subterranean landforms and aquifers

The Blind Cave Eel uses aquatic subterranean habitat, including caves, fissures, sinkholes, wells and groundwater. In the Pilbara it also occurs in shallow alluvial aquifers and permanent surface pools connected with the Robe River system.

Look for suitable habitat in limestone caves, karst voids, fissures, sinkholes, transmissive geological formations and saturated gravel. Cape Range habitat includes Bundera Calcarenite, Exmouth Sandstone and other connected subterranean waterways.

In the Pilbara, habitat includes alluvial aquifers over channel iron deposits, shallow groundwater in river sediments and the phreatic zone beneath the Robe River and its tributaries.

  • Caves and flooded cave passages.
  • Natural sinkholes and rock holes.
  • Artificial wells, exploration bores and pastoral wells.
  • Saturated coarse gravel and sand, especially where connected to river alluvium.
  • Permanent and semi permanent river pools.

Habitat: Water conditions

Cape Range waters can range from fresh to brackish and may be affected by tides. Water is often stratified, with conditions changing through the water column.

The species can move through different salinity levels within anchialine systems. Avoid assuming that only fresh surface water is suitable.

  • Protect groundwater levels and recharge pathways.
  • Prevent sediment, hydrocarbons, wastewater and other contaminants from entering surface or subsurface water.
  • Maintain natural connections between pools, alluvium and groundwater where works occur near rivers.

Habitat: Site features to inspect

During pre clearance inspections, map wells, bores, caves, sinkholes, rock holes, permanent pools, seepage areas and low points that may receive runoff.

Also identify vegetation and soil areas that influence recharge. Hardstand, roads, excavation and drainage changes can alter infiltration and subsurface water movement.

  • Open or filled wells and bores.
  • Karst openings and limestone outcrops.
  • River pools with groundwater influence.
  • Coarse alluvial deposits and saturated gravel.
  • Existing monitoring bores and groundwater dependent vegetation.

Foraging habitat: Food and feeding areas

The Blind Cave Eel feeds near the bottom of subterranean waters. It is associated with soft sediments and organic ooze in crustacean rich cave habitats, but it also forages in groundwater and permanent river pools.

Known prey includes minute Stygiocaris shrimps, Halosbaena tulki, other small crustaceans and cave dwelling arthropods. Terrestrial insects and other material that falls or is washed into the water are also eaten.

Look for suitable foraging habitat where fine sediment, faecal ooze and crustacean communities occur on the bottom of flooded caves, wells or pools.

  • Soft bottom sediments and flocculent organic deposits.
  • Crustacean rich cave pools and anchialine waters.
  • Shallow groundwater connected with alluvial river pools.
  • Permanent pools receiving natural organic inputs.

Foraging habitat: Development risks to feeding habitat

Sediment mobilisation, dewatering, contamination and reduced organic inputs can change the bottom habitat and prey community. These effects may occur outside the visible waterbody if groundwater pathways are connected.

Avoid disturbing bottom sediments in occupied or potentially occupied habitat unless the work has been assessed and approved.

  • Use sediment and erosion controls around pools, bores and drainage lines.
  • Keep fuels, chemicals, concrete washout and wastewater away from recharge areas and surface water.
  • Limit unnecessary pumping and maintain water levels during works.

Breeding habitat: Known breeding information

Very little is known about breeding in the Blind Cave Eel. The subterranean environment makes nests, eggs and young difficult to observe, so all suitable aquatic habitat should be managed as potentially important habitat.

A male guarding a nest or burrow has been reported, but the location, structure and frequency of these sites are not established. Breeding timing, clutch size, age at maturity and recruitment are also unknown.

Do not assume that a lack of visible nests means that breeding is absent.

  • Potential breeding features may include protected spaces in cave sediments, fissures or burrows.
  • Breeding sites may occur below the visible water surface or within connected groundwater.

Breeding habitat: Management around potential breeding habitat

Avoid excavation, pumping, sediment disturbance and changes to water quality in or near occupied groundwater systems. If a proposed action could affect a cave, bore, pool or aquifer, seek advice from a threatened fish or subterranean fauna specialist before work starts.

There are no established seasonal timing windows for breeding. Plan works to avoid habitat disturbance wherever practicable rather than relying on a seasonal restriction.

  • Retain natural water levels and groundwater connections.
  • Prevent infilling or contamination of wells, sinkholes and cave openings.
  • Stop work and obtain advice if fish are observed in a work area or dewatered habitat.

Sheltering habitat: Shelter features to look for

The Blind Cave Eel shelters in dark aquatic environments and can burrow into soft bottom deposits. It may use caves, fissures, wells, sinkholes, groundwater and connected surface pools.

Potential shelter occurs in flooded caves, fissures, soft sediments, cave floor ooze and the spaces beneath river alluvium. Artificial wells and bores may provide access to the same groundwater systems.

Individuals are rarely seen and may remain below the surface or close to the bottom.

  • Flooded cave chambers and passages.
  • Fissures and karst voids.
  • Soft sediment and organic ooze.
  • Pastoral wells, monitoring bores and exploration bores.
  • Deep or shaded sections of permanent pools.

Sheltering habitat: Working near shelters

Do not enter caves or descend into wells as part of routine fauna work. Many Cape Range caves are vertical, unstable and may contain dangerous carbon dioxide concentrations. Use experienced caving personnel and a site specific safety plan where access is necessary.

Keep bore and pool works controlled. Prevent collapse, infilling, rapid drawdown and contamination of connected habitat.

  • Fence or otherwise control access to hazardous openings.
  • Use non destructive observation and environmental DNA methods where suitable.
  • Maintain records of water level, water quality and any fish observations before, during and after works.

Threats: Clearing and hydrological change

The main development risks are changes to groundwater, surface water and water quality. Because the species can occupy connected habitat that is not visible from the surface, impacts must be considered across the wider hydrological system.

Clearing riparian vegetation, altering drainage or covering recharge areas can change surface flows, groundwater recharge and water levels. These changes may affect river pools, alluvial aquifers and subterranean habitat.

Avoid clearing riparian vegetation and groundwater dependent vegetation where practicable. Keep natural flow paths and infiltration areas functional.

  • Stage clearing so habitat is not left exposed or disconnected for extended periods.
  • Do not divert, block or concentrate flows into occupied pools or recharge areas.
  • Use watercourse management measures that prevent impacts to surface water flow.

Threats: Excavation, dewatering and vibration

Footings, trenches, pits, quarrying and bore construction can damage voids, fissures and saturated sediments. Dewatering can reduce water levels or alter connections between groundwater and surface pools.

Construction vibration may disturb subterranean habitat and can contribute to structural damage where caves or voids are present.

  • Assess subsurface habitat before excavation or bore installation.
  • Minimise the footprint and duration of dewatering.
  • Retain habitat and avoid unnecessary vibration near caves, sinkholes, bores and permanent pools.

Threats: Contamination and sediment

Sediment, hydrocarbons, chemicals, wastewater and concrete residues can enter surface pools or groundwater. Subterranean systems may have limited flushing and contamination can persist beyond the work area.

Use strong spill prevention, erosion control and wastewater management from site establishment through to rehabilitation.

  • Store fuels and chemicals away from waterbodies, bores and recharge areas.
  • Install and maintain sediment controls before ground disturbance.
  • Do not discharge untreated water into pools, drainage lines or the ground.
  • Inspect and rehabilitate disturbed areas promptly to reduce ongoing sediment input.

Threats: Invasive species and habitat loss

Introduced aquatic animals can compete with or prey on subterranean fauna. Filling wells, sealing openings, removing pools or fragmenting groundwater habitat can also remove access to occupied systems.

Protect known and potential habitat even where the species has not yet been recorded.

  • Prevent movement of aquatic organisms between sites by cleaning and drying equipment.
  • Retain connected caves, wells, pools, alluvial sediments and recharge areas.
  • Record and report any suspected Blind Cave Eel or unusual subterranean fauna observation.
  • Obtain threatened species advice before relocating fauna, filling a well or altering a groundwater system.

Survey methodology: 1. Desktop assessment

The Blind Cave Eel is rarely detected and occurs in groundwater, caves, fissures, wells and some permanent surface pools. Surveys must be designed by a subterranean fauna ecologist and undertaken by suitably trained cave personnel.

Map all known and potential subterranean habitat before planning access or disturbance.

Treat groundwater, caves, sinkholes, wells, alluvial aquifers, the phreatic zone and permanent river pools as potential habitat where they occur in or near the work area.

Review records from the Cape Range, Barrow Island and Robe River catchment, including Bungaroo Creek and Jimmawurrada Creek.

Check whether the work could alter groundwater recharge, surface flows, water quality, salinity, sediment movement or access to subterranean voids.

Commonwealth status: Vulnerable under the EPBC Act

Western Australian status: Vulnerable

Known Australian range: Western Australia, including Cape Range, Barrow Island and parts of the Pilbara

Survey methodology: 2. Field detection

Use daytime visual searches from wells, sinkholes and other safe openings. Inspect the bottom of the water column and soft faecal or flocculent sediments.

Use daytime snorkelling only where the site is safe, access is authorised and the survey team has suitable cave and diving skills.

Use headlamps for night observation from above wells or openings where this can be done safely. Detection has also been recorded through eDNA sampling and specimen collection.

Do not enter vertical, unstable or carbon dioxide affected caves without a documented confined-space and cave safety plan.

Survey methodology: 3. Timing and effort

Plan repeat visits where access, safety or water conditions limit detection. A single negative visit should not be treated as evidence of absence.

Use daylight conditions for visual survey and capture work. Previous survey guidance indicates that methods without direct sunlight before capture have not been successful for this species.

There is no established seasonal migration period or breeding season to use for survey timing. Schedule surveys when the habitat can be examined safely and without changing water levels or water quality.

Use eDNA where direct observation is unlikely, and collect confirmatory specimens only when authorised and necessary.

Survey methodology: 4. Survey records

Record the date, time, weather, water level, water temperature, salinity, pH where measured, visibility and survey duration.

Map each opening, pool, bore, cave, fissure and sampling point. Record whether the location is groundwater, surface water or an anchialine system.

Record the number of animals seen, their approximate size, position in the water column, association with sediment, and any feeding or nesting behaviour.

Retain photographs, eDNA sample identifiers, capture records, permits, observer names and access or safety constraints.

Before habitat disturbance: 1. Approvals and permits

Avoid disturbance to subterranean waterways wherever practicable. Because breeding biology and population structure are poorly known, protect the whole connected water and sediment system rather than relying on a small site buffer.

Screen the action under the EPBC Act before clearing, excavation, dewatering, drilling, road construction or changes to surface drainage.

Refer the action if the assessment indicates a likely significant impact on the species or its habitat.

Obtain Western Australian approvals and fauna permits before handling, trapping, collecting, sampling or relocating animals.

Confirm animal ethics and animal care approvals for vertebrate sampling. Use an approved subterranean fauna specialist for any collection or eDNA program.

For work in Queensland, check whether a species management program is required if a listed near threatened animal or its breeding place could be affected. The Blind Cave Eel is currently known from Western Australia, so confirm the species and jurisdiction before applying this pathway.

Before habitat disturbance: 2. Avoidance and site controls

Redesign work to avoid caves, sinkholes, wells, groundwater dependent vegetation, permanent pools, riparian areas and known or potential subterranean waterways.

Keep excavation, piling, drilling, blasting, dewatering, spoil storage, fuel storage and waste facilities away from connected groundwater and surface pools where practicable.

Maintain surface water flows and groundwater recharge. Prevent sediment, hydrocarbons, chemicals, wastewater and concrete washout from entering the drainage or aquifer.

Do not fill, seal, drain or modify a cave, well, bore or sinkhole without specialist assessment and approval.

Before habitat disturbance: 3. Survey and exclusion planning

Complete the pre-disturbance survey before clearing, excavation or dewatering begins. Include all accessible wells, bores, pools, caves, sinkholes and likely subsurface habitat.

Set site-specific exclusion zones around occupied or potentially connected habitat with the relevant regulator and subterranean fauna specialist. No standard species-specific buffer is established for this fish.

Mark exclusion zones on plans and on the ground. Fence or barricade openings and pools where people, vehicles or plant could enter.

Do not rely on a surface-only inspection to clear an area where groundwater or subsurface voids may be affected.

Before habitat disturbance: 4. Timing and induction

There is no confirmed breeding or migration calendar for the Blind Cave Eel. Do not schedule works on the assumption that a particular month is low risk.

Plan works outside periods of high flow, flooding or other conditions that could spread sediment or contaminants through connected habitat.

Induct all workers on the species, protected habitat, exclusion zones, spill response, stop-work authority and reporting requirements.

Provide a site map showing no-go areas, emergency contacts, access controls and the location of clean water, spill kits and decontamination equipment.

During habitat disturbance: 1. Sequential clearing and work control

Use a staged, low-impact work sequence and keep a qualified fauna spotter catcher or aquatic fauna specialist involved where habitat may be affected. Stop work immediately if an animal, breeding site or connected subterranean habitat is found.

Clear in stages from the least sensitive area towards retained habitat. Keep exclusion zones intact until the work area is stable and inspected.

Install erosion and sediment controls before ground disturbance. Maintain drainage paths and prevent turbid water from entering pools, bores, caves or alluvial sediments.

Use the smallest practicable excavation, access track and working area. Avoid unnecessary vibration, drilling, blasting and changes to groundwater levels.

Require the fauna spotter catcher or nominated specialist to inspect each stage before plant moves into the next work area.

During habitat disturbance: 2. Stop-work and handling

Give the fauna spotter catcher authority to stop work without delay.

Do not touch, chase, net, relocate or collect a Blind Cave Eel unless the person is authorised under the relevant permit and approved method.

If an animal is found, isolate the area, keep people and equipment clear, prevent changes to water quality and contact the project ecologist and regulator.

Use clean, wet equipment and approved aquatic hygiene procedures if handling has been authorised. Do not transfer water, sediment or animals between catchments.

During habitat disturbance: 3. Breeding places and occupied habitat

Treat any nest, burrow, guarded area, aggregation or repeated animal observation as potentially important habitat.

Stop work around the location and do not disturb the substrate, water level, sediment or nearby groundwater pathway.

Have the ecologist assess whether the location is an active breeding place or connected habitat. Obtain any additional approval before resuming work.

Do not install temporary structures over an opening or pool, or pump water from it, until the site has been assessed.

During habitat disturbance: 4. Injured animals and records

Do not release an injured animal into an unconnected waterbody. Keep it in suitable clean water only under the direction of an authorised aquatic fauna specialist.

Contact the project ecologist, wildlife authority and permit holder immediately. Arrange veterinary or specialist care where available.

Record the location, time, condition, photographs, handling steps, water source, personnel, permits and final outcome.

Report deaths, unauthorised handling, habitat damage, spills, dewatering events and breaches of exclusion zones through the project incident system and to the relevant regulator.

After habitat disturbance: 1. Post-clearance checks

Post-work checks should confirm that habitat remains connected, water quality is suitable and no animals have been stranded or injured. Monitoring should match the scale and risk of the disturbance and continue where the project changes groundwater or surface-water conditions.

Inspect the work area, access routes, drainage controls, pools, bores and nearby openings after each clearing or excavation stage.

Check for stranded animals, blocked flow paths, sediment entry, spills, exposed voids, changed water levels and damage to riparian or groundwater dependent vegetation.

Remove temporary materials, spoil and waste that could enter water or block recharge.

Keep exclusion fencing in place until the ecologist confirms that the area is safe and stable.

After habitat disturbance: 2. Monitoring and verification

Monitor water levels, flow, turbidity, salinity and other project-specific water quality variables where works could affect groundwater or surface pools.

Repeat visual or eDNA surveys where the approval, risk assessment or specialist advice requires confirmation of occupancy after works.

Compare results with baseline records and investigate any sustained change in water quality, water level, surface flow or subterranean access.

Use the same sampling locations and methods where possible so results can be compared over time.

After habitat disturbance: 3. Relocated animals and follow-up

Track every authorised relocation from capture through release. Record the source location, release location, water conditions, handling time and animal condition.

Release animals only into approved, suitable and connected habitat. Do not move them between catchments or into isolated pools without written approval.

Inspect release sites for mortality, stranding, unusual behaviour and changes in water quality.

Stop further relocation if animals show repeated injury, mortality or poor condition, and obtain specialist and regulatory advice.

After habitat disturbance: 4. Reporting and review

Submit survey, incident, handling, eDNA and monitoring records in the format required by the approval or permit.

Update the site risk assessment when new records extend the known distribution or reveal a connected habitat pathway.

Hold an incident review after any animal death, spill, dewatering event, unauthorised entry or breach of the exclusion zone.

Use the review to revise induction material, work methods, monitoring locations and emergency contacts before the next work stage.

Rehabilitation actions: 1. Restore water and substrate

Rehabilitation should restore groundwater recharge, surface-water flow, water quality and the physical connection between aquatic habitats. The Blind Cave Eel has specialised subterranean habitat, so broad terrestrial revegetation alone will not replace damaged habitat.

Remove temporary hardstand, spoil and barriers that restrict infiltration or surface-water flow, where removal is approved and safe.

Stabilise disturbed ground with local materials and prevent sediment from entering pools, bores, caves, fissures and alluvial aquifers.

Restore riparian and groundwater dependent vegetation where it protects recharge areas or water quality.

Do not seal, fill or modify subterranean openings as part of rehabilitation without specialist assessment.

Rehabilitation actions: 2. Contamination and weeds

Remove contaminated soil, absorbents, fuel, waste and construction materials in accordance with the site contamination plan.

Control weeds around recharge areas and drainage lines using methods that do not introduce herbicide or sediment into groundwater or pools.

Use clean fill and local, uncontaminated materials. Do not introduce foreign water, sediment, fauna or organic waste into aquatic habitat.

Inspect rehabilitation areas after rainfall and repair erosion or sediment controls promptly.

Rehabilitation actions: 3. Structures and habitat replacement

Do not install nest boxes, bat boxes, artificial nest sites, roost structures or terrestrial replacement shelters for this fish.

There is no established artificial breeding structure for the Blind Cave Eel. Replace habitat through protection and restoration of suitable water, sediment, fissures, caves, wells and groundwater pathways.

If a subsurface structure must be replaced, have its design approved by a subterranean fauna specialist and the relevant regulator before construction.

Ensure replacement or retained habitat remains connected to the local groundwater and surface-water system.

Rehabilitation actions: 4. Water, lighting and long-term monitoring

Maintain natural or approved water levels, recharge and flow paths. Do not discharge untreated water into habitat.

Limit lighting near wells, sinkholes, caves and surface pools. Use shielded, low-spill lighting and switch it off when not required.

Monitor rehabilitated sites for water quality, sedimentation, vegetation recovery, erosion, groundwater levels and species presence where required.

Continue monitoring for the period set by the approval, with additional surveys after major rainfall, dewatering, spills or other events that could affect connected habitat.

Sources