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Drysdale Grunter (Syncomistes rastellus)

The Drysdale grunter is a freshwater fish recorded from the Gibb and Drysdale Rivers and described more broadly from coastal rivers in northern Western Australia. Its habitat and ecology are poorly documented, so potential works in its river habitat warrant careful assessment.

Conservation status

Western Australia, WA Threatened and Priority Fauna List: Priority 2.

Seasonal planning

Species-specific information on seasonal activity or breeding has not been documented. Plan survey and works timing around site conditions, approvals and project risk rather than an assumed seasonal pattern.

Seasonal timing for this species has not been established.

  • Survey and works planning: Planning window only. Species-specific activity and breeding months are not recorded; obtain site-specific ecological advice before works.

Identification: Appearance and size

Field identification details are limited. Confirm suspected records with an experienced freshwater fish ecologist.

The Drysdale grunter belongs to the grunter family, Terapontidae. Its colour, body shape, diagnostic features and size have not been documented.

Identification: Similar species

Other Syncomistes species occur in north-western Australia. Head features, particularly the jaw and dentition, are important for distinguishing taxa, and some characters change as fish grow. A field key for separating this species from similar fish is not available.

Identification: Field signs

No distinctive signs, such as nests or other traces, are reported. A fish observation or a specimen assessed by a qualified specialist is needed to support identification.

Distribution: Known range

The species is reported from northern Western Australia, and the DBCA priority listing identifies the Kimberley region.

The Drysdale grunter is reported from the Gibb and Drysdale Rivers and from coastal rivers in northern WA.

Atlas of Living Australia records show 128 WA records across 16 distinct 0.1-degree locations, spanning latitude -17.3 to -14.5 and longitude 126 to 128.5. These aggregated coordinates do not identify named sites.

Distribution: WA listing region

The DBCA Threatened and Priority Fauna List dated 1 July 2025 flags the Kimberley region. The species is listed as Priority 2, a DBCA priority category, and is not a listing under the Biodiversity Conservation Act 2016. It has no national listing.

Distribution: Records and uncertainty

The species is poorly known and recorded from few locations. Atlas record totals are not a substitute for site-level verification. Records outside WA were excluded from the regional summary as likely errors.

Habitat: Reported river habitat

The Drysdale grunter is a riverine freshwater fish, but its habitat is only broadly described.

The species is reported to prefer main river channels over tributaries. It is associated with flowing water, with variable turbidity and substrate.

Habitat: Site assessment

Water depth, channel dimensions, vegetation, water quality limits and other fine-scale habitat features are not documented. Do not use any one of these features alone to rule out the species.

Foraging habitat: Reported diet

The species is herbivorous and grazes on filamentous algae. Feeding locations and seasonal changes have not been documented.

The Drysdale grunter is herbivorous and grazes on filamentous algae.

Foraging habitat: Foraging locations

Particular feeding substrates, depths or microhabitats are not documented. Algae at a site is not evidence that the fish is present.

Breeding habitat: Known information

Breeding biology is poorly known.

Breeding seasons, spawning locations, egg or young-fish characteristics, and parental behaviour have not been documented.

Breeding habitat: Precaution

Do not assume that any particular season is free of breeding activity. Where works could affect river habitat, assess and manage potential effects without relying on an unverified breeding calendar.

Sheltering habitat: Known information

Sheltering behaviour and specific refuge features have not been documented.

The species is reported to prefer main river channels over tributaries, but shelter sites, resting areas and refuge habitat have not been identified.

Sheltering habitat: Precaution

Avoid assuming that any particular bank, substrate or channel feature is unimportant. Where a waterway may be affected, assess the connected channel habitat and avoid unnecessary disturbance.

Threats: Documented status

Specific threats to the species have not been identified.

The species is poorly known and recorded from few locations.

Threats: Works-related precautions

Development activities are not established as documented threats. As a precaution, assess potential effects of works that could alter flowing river channels, turbidity, substrates or algal resources, which relate to the broad habitat and diet information reported for the fish.

Survey methodology: 1. Desktop assessment

Survey methods and the species' detectability have not been documented. Use qualified aquatic surveyors and methods appropriate to the site and approvals.

Review current records, waterway mapping and available site information for the Gibb and Drysdale River region and other northern WA coastal rivers. Treat regional atlas records as context, not confirmation of a site record.

Survey methodology: 2. Site inspection

Inspect the proposed work area and connected river channel, noting flow, turbidity, substrate and potential algal resources. These are broad features mentioned in the species account, not a complete habitat model.

Survey methodology: 3. Aquatic survey

Have a suitably qualified fish ecologist select and conduct permitted aquatic survey methods appropriate to the waterway and project. Record survey conditions, effort, locations, identifications and any limitations. No species-specific method, survey season or detection probability has been established.

Survey methodology: 4. Identification and reporting

Seek expert confirmation for suspected records, particularly where similar Syncomistes may occur. Retain appropriate evidence and report observations through the project and relevant regulatory channels, following permits and animal-handling requirements.

Vegetation associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific vegetation association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Ecosystem associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific ecosystem association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Soil and substrate associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific soil association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Water and wetland associations: Water-associated habitat mentioned in profile

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

The species is reported to prefer main river channels over tributaries.

Automatically indexed from existing profile text. Not a verified preference, mapped occurrence or habitat requirement. Check the original source and regional qualifiers before use.

Evidence: Unreviewed profile-derived candidate

Confidence: Not independently verified

Region: Scope as described in the quoted profile text; not independently verified. Profile states: WA.

Habitat use: general

Attribution gap: No sentence-level reference is attached to the original profile block. Review the profile bibliography; this candidate is not source-verified.

Fauna records and mapped habitat: Not yet analysed

Record locations can be overlaid with mapping, but record frequency alone does not measure habitat preference. No species is excluded from desktop assessments by this analysis.

No quality-controlled record-to-map analysis has been completed for this species. The existing generalised distribution dots and indicative range polygons have not been treated as precise occurrence coordinates.

A defensible run needs dated, independently attributable records, coordinate uncertainty, duplicate and captive-record checks, layer versions and regional scope. Preference and absence require additional survey-effort and detection evidence.

Habitat limitations and contrary evidence: No supported exclusion recorded

Not recorded is not the same as cannot occur. Low suitability, resident habitat, breeding habitat and occasional movement are different conclusions.

This library has not established a vegetation, ecosystem or soil-type exclusion for this species. This does not mean all habitat is suitable; the evidence needed to justify an exclusion has not been assembled.

Habitat limitations and contrary evidence: Before using a negative association

  • Confirm the taxon, geographic region, life stage and habitat function covered by the evidence.
  • Check survey methods, season, repeated effort and detectability before interpreting non-detection.
  • Investigate credible contradictory records and microhabitats absent from broad mapping.
  • Do not convert a missing map class, low record count or failed data request into species absence.

Before habitat disturbance: 1. Map the work area

Plan works on the assumption that site occupancy may be uncertain where suitable river habitat is present.

Map the proposed disturbance footprint, access routes and any connected river channels that could be affected. Check the location against available records and the reported regional range.

Before habitat disturbance: 2. Set survey and approval needs

Obtain advice from a qualified aquatic ecologist and confirm required permits, approvals and biosecurity measures before any fish survey or in-water work. Species-specific survey timing has not been established.

Before habitat disturbance: 3. Plan avoidance

Avoid or minimise disturbance to flowing main-channel habitat where practicable. Plan controls to limit unintended changes to turbidity, channel substrate and algal resources.

During habitat disturbance: 1. Work to the approved footprint

Keep disturbance controlled and respond promptly to fish observations or changes in waterway conditions.

Keep vehicles, machinery, equipment and clearing within marked work limits. Do not enter or disturb the channel unless the work is authorised and the relevant controls are in place.

During habitat disturbance: 2. Manage waterway effects

Use project-specific controls to avoid unnecessary sediment or other material entering the water, and to minimise changes to channel flow and substrate. Species-specific thresholds have not been established.

During habitat disturbance: 3. Respond to fish

If a suspected Drysdale grunter is seen or captured, pause nearby activity where safe, avoid unnecessary handling and contact the project ecologist. Any capture, handling or relocation must be directed by appropriately qualified personnel and comply with approvals.

During habitat disturbance: 4. Record changes

Document the location, date, work activity, waterway conditions and any fish observations or unexpected disturbance. Escalate incidents through the project environmental procedures.

After habitat disturbance: 1. Inspect the site

Check that controls have been removed or stabilised as planned and that affected waterway areas are being managed as required.

Inspect the work area and adjacent channel for residual disturbance, displaced items or continuing effects on flow, turbidity and substrate. Record findings and arrange corrective action where needed.

After habitat disturbance: 2. Report and retain records

Retain survey data, fish observations, photographs and incident records with the project environmental documentation. Share relevant confirmed records with the appropriate project and regulatory contacts.

Rehabilitation actions: 1. Stabilise affected areas

There is no species-specific rehabilitation prescription. Restore affected areas in line with project approvals and ecological advice.

Stabilise disturbed banks and work areas using site-appropriate methods, while avoiding unapproved changes to the river channel or its substrate.

Rehabilitation actions: 2. Review recovery

Check rehabilitation against the approved objectives and monitor for continuing effects on channel flow, turbidity, substrate and algal resources where relevant. Visible algae or general site recovery does not prove that the fish is present or that habitat function has recovered for this species.

Sources