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Flatback Mangrovegoby (Mugilogobius platynotus)

A small Australian goby found mainly in shallow mangrove, saltmarsh and tidal creek habitat. In Victoria it is restricted to Westernport, where loss or isolation of mangrove habitat, altered water quality and changes to freshwater and tidal flows are relevant risks during coastal development and infrastructure works.

Conservation status

Victoria, Flora and Fauna Guarantee Act 1988: Endangered.

Breeding season

The supplied sources do not establish a breeding calendar. The only seasonal pattern reported is higher abundance in mangrove and saltmarsh habitat in autumn and spring at Botany Bay, so clearing risk should be managed year-round in occupied or connected habitat.

Seasonal information is limited. The autumn and spring pattern comes from Botany Bay, New South Wales, and should not be applied as a confirmed breeding calendar across Queensland, New South Wales and Victoria.

  • Highest local abundance: Higher abundance was recorded in autumn and spring at Botany Bay, New South Wales. The source does not provide month-by-month counts, so April, October and November are shown as indicative seasonal peaks only at the season level, not as species-wide breeding peaks.
  • Movement and habitat use: The species is associated with permanent mangrove habitat at one studied site, and records include tidal estuaries, marine inlets and lower coastal streams. No migration or dispersal months are specified.
  • Highest clearing risk: Risk is treated as year-round because breeding and young stages are not seasonally defined, and habitat loss, pollution and hydrological change can affect occupied Victorian habitat at any time. Autumn and spring warrant particular attention because higher local abundance has been recorded then.

Identification

This is a small, slender goby with a relatively flat, broad head and a large, slightly oblique mouth. It is usually associated with shallow estuarine water, mangroves and soft sediment rather than open channels.

Adults are usually up to 50 mm total length, with a maximum recorded size of 65 mm and weight of 4.0 g. The body is generally mottled brown to pale yellowish brown, with a series of indistinct darker midlateral spots or blotches, fine vermiculation on the head and a small dark spot at the middle of the caudal-fin base.

Body size: Usually to 50 mm total length; maximum 65 mm.

Weight: Up to 4.0 g.

Colour: Brownish mottling, darker midlateral spots or blotches, and a dark spot at the caudal-fin base.

  • The head is wider than deep and relatively flat when viewed from above.
  • The mouth is large, subterminal and slightly oblique. In adult males the jaws extend past the rear margin of the eye, while in females they generally reach to below the front half of the eye.
  • The first dorsal fin is low and rounded, with the first to fifth spine tips usually free. A dark or blackish spot is commonly present near the rear of the first dorsal fin, particularly in adult males.

Identification: Diagnostic features

The species has no head pores, as is typical of Mugilogobius. It has mostly cycloid body scales, with ctenoid scales restricted mainly to a patch behind the pectoral fin and the caudal peduncle.

Predorsal scales: 0 to 21, mean about 4.

Longitudinal scales: 45 to 59.

Pectoral rays: 13 to 17.

Head pores: Absent.

  • Predorsal scales are absent or sparse, with 0 to 21 small scales and a mean of about 4. This is a useful distinction from Mugilogobius stigmaticus, which generally has 17 to 30 predorsal scales, with a mean of about 22.
  • The species has 45 to 59 longitudinal scales and generally 16 to 22 circumpeduncular scales.
  • The pectoral fin has 13 to 17 rays, and the second dorsal and anal fins generally have 1,8 to 10 rays.
  • Mugilogobius platynotus has a relatively low metapterygoid and mostly cycloid body scaling. These characters may require a specimen or clear close-range photographs for confirmation.

Identification: Field signs and sex differences

There are no useful tracks, scats, calls, nests, sloughs or eyeshine to search for. A live fish may be detected in shallow water, among mangrove roots, organic debris or soft sediment, and may perform aerial surface respiration when dissolved oxygen is low.

Low-oxygen response: Aerial surface respiration has been recorded below about 0.9 g/L dissolved oxygen.

Sexual difference: Adult males generally have a broader head and longer jaws than females.

  • At oxygen levels below about 0.9 g/L, fish may beach themselves just below the water surface with the mouth at the surface, hang vertically with the mouth at the surface, gulp air or increase gill ventilation.
  • Handle observations carefully because surface respiration can also indicate stressful water quality or capture conditions.
  • Adult males generally have a broader head and longer jaws than females. Male jaws may extend past the rear of the eye, while female jaws generally reach below the front half of the eye.
  • Colour and fin markings vary with sex, size and preservation, so they should not be used alone for identification.

Distribution: National range

The Flatback Mangrovegoby is endemic to Australia and occupies tidal estuaries, marine inlets and some lower coastal freshwater reaches. Victorian records are concentrated in Westernport, making that embayment the principal known Victorian stronghold.

The documented range extends from southern Queensland, including Moreton Bay, through coastal New South Wales to eastern Victoria. Records include near-shore islands, estuarine inlets, mangrove sites, coastal lagoons and lower reaches of coastal rivers and creeks.

State and territory range: Queensland, New South Wales and Victoria.

Biogeographic description: Temperate to subtropical south-eastern Australian coastal estuaries and marine inlets.

Victorian stronghold: Westernport.

  • Queensland: southern Queensland and Moreton Bay, including Coomera Island and Moreton Island records.
  • New South Wales: coastal estuaries and inlets including Port Hacking, Botany Bay, Sydney Harbour, Jervis Bay, Batemans Bay and other coastal rivers and lagoons.
  • Victoria: Westernport, including records from Blind Bight and habitat near Tooradin. The supplied sources do not confirm current populations in other Victorian bays or inlets.

Distribution: Known concentration and population status

Populations can be patchy but locally abundant. The species has been recorded as dominant in some mangrove habitats, although abundance varies between seasons and among microhabitats.

Victorian extent of occurrence: Estimated at 570 km² from accepted post-1970 Victorian records.

Victorian area of occupancy: Estimated at 52 km² using 2 km by 2 km grid cells.

Number of Victorian locations: Estimated at one location, Westernport.

Mature population size: Not known; the assessment states there is insufficient evidence to determine the number of mature individuals.

  • In Westernport, all known Victorian populations occur within one coastal embayment and may be exposed to the same major threats.
  • Within mangroves, abundance has been higher in the mangrove forest than along the seaward edge or on adjacent mudflats.
  • A three-year study described the species as a permanent resident of a mangrove site in Botany Bay, New South Wales.

Habitat: Water and sediment

The species uses shallow, usually clear to slightly turbid water in tidal estuaries, bays, inlets, coastal lagoons and lower coastal streams. In Victoria it is associated with upper estuarine reaches close to freshwater inflow and with stands of Grey Mangrove, Avicennia marina.

Typical habitat includes shallow tidal water over soft mud or sand and mud. Fish may occur in flowing freshwater reaches immediately upstream of tidal influence, but the species is also recorded in fully marine environments.

Recorded conductivity range: About 56,000 microSiemens per centimetre in fully marine environments to about 1,300 microSiemens per centimetre in a lower coastal stream just upstream of tidal influence.

Recorded water temperature: Up to 27.5 degrees Celsius.

Oxygen tolerance: The species can tolerate low dissolved oxygen and has performed aerial surface respiration below about 0.9 g/L.

  • Retain shallow channels, pools, creek margins and inundated depressions connected to estuarine water.
  • Avoid isolating shallow mangrove habitat from tidal exchange or freshwater inflow.
  • Treat soft mud, sand and mud, organic debris and small intertidal structures as potential habitat rather than as vacant substrate.

Habitat: Vegetation and structure

The species is closely associated with saltmarsh and mangroves, especially Grey Mangrove, Avicennia marina. In Victoria it is restricted to upper estuarine mangrove habitat near freshwater inflow.

Key vegetation: Grey Mangrove, Avicennia marina, with associated saltmarsh.

Substrate: Soft mud or sand and mud.

Water depth: Shallow water; a precise depth range is not given in the supplied sources.

Elevation: No elevation limit is given. Habitat is tidal or close to tidal influence.

  • Prioritise mangrove forest, not only the seaward mangrove edge or adjacent bare mudflat, when assessing potential habitat.
  • Retain mangrove roots, shallow channels, organic debris and tunnels made by other species.
  • Check adjacent saltmarsh, creek edges and lower coastal river reaches where they remain hydrologically connected to mangrove habitat.

Foraging habitat: Diet

The Flatback Mangrovegoby is mainly carnivorous, but its diet changes with season and includes both animal prey and plant or organic material. It feeds within mangrove and saltmarsh habitat and associated shallow estuarine water.

Recorded food includes culicid larvae, other insects such as dipterans, arachnids, crab larvae and adult crabs, copepods, amphipods, prawns, juvenile fish, algae and detritus.

Feeding type: Mainly carnivorous, with seasonal dietary changes.

Animal prey: Insect larvae and adults, arachnids, crabs, copepods, amphipods, prawns and juvenile fish.

Other food: Algae and detritus.

  • Inspect shallow mangrove pools, creek margins, saltmarsh inlets and organic debris where small crustaceans and insect larvae may occur.
  • Do not assume that only open water is foraging habitat. The species is more abundant within mangrove forest than along the seaward edge or on adjacent mudflat in some studies.
  • Avoid releasing turbid, contaminated or oxygen-depleted water into feeding areas.

Foraging habitat: Foraging area

The supplied sources do not give a home-range size, daily movement distance or territory size. The species has been recorded as a permanent resident at a mangrove site, so local feeding habitat may be used repeatedly rather than only during passage.

Foraging range: Not quantified in the supplied sources.

Seasonal abundance: High abundance has been recorded in mangrove and saltmarsh habitat in autumn and spring at Botany Bay, New South Wales.

  • Maintain connected mangrove forest, shallow channels and nearby saltmarsh so fish can move between feeding microhabitats with the tide.
  • During works, inspect any trapped or dewatered pools for fish before filling, draining or covering them.
  • Use fish rescue and relocation procedures developed by an aquatic ecologist where works affect occupied shallow habitat.

Breeding habitat: Breeding facts

The supplied documents do not provide a confirmed breeding season, nest description, spawning substrate, egg count, larval period or parental care information for this species. Breeding assessments should therefore treat occupied shallow mangrove and tidal creek habitat as potentially important throughout the year.

Breeding season: Not stated in the supplied sources.

Mating behaviour: Not stated in the supplied sources.

Egg or clutch size: Not stated in the supplied sources.

Gestation or incubation: Not applicable or not stated. A larval development period is not provided.

Age at maturity: Not stated. The projected generation length is 3 years, based on maturity information from similar-sized gobies.

Lifespan: Not stated in the supplied sources.

Breeding habitat: Breeding habitat precautions

No breeding structure is described in the supplied documents. Until site-specific information is available, shallow mangrove forest, tidal creek margins, soft sediment, organic debris and tunnels of other species should be retained and protected from direct disturbance.

Generation length: Projected at 3 years.

Known breeding site: No specific breeding site is identified in the supplied sources.

  • Plan works to avoid draining, filling, isolating or heavily disturbing connected shallow mangrove and upper estuarine habitat at any time of year.
  • Use aquatic surveys before dewatering or excavation because a lack of visible fish at one tide does not demonstrate that the habitat is unused.
  • Keep water quality, dissolved oxygen, salinity and tidal or freshwater connections within the existing site range where practicable.

Sheltering habitat: Known refuges

Shelter is provided by mangrove forest, soft sediment, organic debris and tunnels made by other species. The fish also uses surface-associated positions during low oxygen conditions, but this behaviour indicates physiological stress rather than a preferred refuge.

The species is found among organic debris and in tunnels of other species on soft mud or sand and mud substrates. Abundance is often higher within mangrove forest than along the seaward edge or adjacent mudflat.

Shelter type: Mangrove forest, organic debris and tunnels of other species.

Substrate: Soft mud or sand and mud.

Shelter dimensions: Not quantified in the supplied sources.

  • Retain mangrove root structure, natural debris, soft sediment and occupied animal tunnels where works are proposed.
  • Avoid removing or burying shallow pools and creek margins that provide cover at different tidal stages.
  • Inspect isolated pools, culverts, trenches and excavations before dewatering or backfilling.

Sheltering habitat: Low-oxygen behaviour

During low dissolved oxygen, fish may hold the mouth at the water surface, hang vertically in the water column, gulp an air bubble for less than one minute before exchanging it, and increase gill ventilation.

Surface respiration threshold: Observed below about 0.9 g/L dissolved oxygen.

Air bubble duration: Usually held for less than one minute before exchange.

  • Treat fish at the surface or near the waterline as potentially stressed and check dissolved oxygen, temperature, salinity and contamination before handling.
  • Do not interpret aerial surface respiration as evidence that the habitat is unimportant or that fish can safely remain during dewatering.
  • Provide shaded, oxygenated holding water and seek aquatic fauna advice if capture is required.

Threats: Habitat loss and fragmentation

Loss and degradation of mangrove habitat are the main documented threats. The Victorian population is especially exposed because known Victorian records are restricted to Westernport, where a major pollution event or broad hydrological change could affect many fish at the same time.

Mangrove loss associated with urbanisation, industrial development, pollution and sea level rise is identified as the main threat. Clearing, reclamation, hard shore protection and loss of tidal connectivity can remove shallow habitat and separate mangrove patches.

Primary threat: Loss of mangrove habitat.

Documented drivers: Urbanisation, industrial development, pollution and climate-change-associated sea level rise.

Victorian vulnerability: All known Victorian populations occur in Westernport, estimated as one location.

  • Avoid clearing Grey Mangrove stands, upper estuarine creek margins and connected saltmarsh where practicable.
  • Keep construction access, laydown areas and spoil outside mangrove and shallow intertidal habitat.
  • Do not treat a narrow mangrove strip, isolated pool or soft-sediment margin as having low value without an aquatic habitat assessment.
  • Maintain connections between mangrove forest, tidal creeks, saltmarsh and nearby freshwater inflows.

Threats: Water quality and hydrology

Chemical spills and other water pollution may rapidly affect the species because the Victorian distribution is restricted to one embayment. The fish can tolerate broad salinity conditions and low oxygen, but specific tolerances of eggs and larvae are unknown.

Water pollution risk: Chemical spills may rapidly affect the taxon.

Known tolerance limits: General salinity tolerance is broad, but detailed short-term and long-term tolerances are poorly known.

  • Prevent fuel, sediment, concrete washout, chemicals and other contaminants from entering mangrove creeks, drains, pools or Westernport.
  • Avoid sudden changes to salinity, freshwater inflow, tidal exchange, temperature and dissolved oxygen.
  • Use staged dewatering and water-quality monitoring where works affect occupied shallow habitat.
  • Treat newly shed eggs and hatched larvae as having unknown salinity tolerance.

Threats: Construction and other pressures

The supplied sources do not identify species-specific evidence for roads, fire, introduced predators or disease. These pressures may still matter indirectly where they remove mangrove cover, alter drainage, increase sediment or pollutant inputs, or affect fish during capture and relocation.

Road impacts: No species-specific road-impact evidence is provided in the supplied sources.

Fire impacts: No species-specific fire-impact evidence is provided in the supplied sources.

Predators and disease: No species-specific evidence is provided in the supplied sources.

  • Keep vehicles and machinery out of shallow water, mangrove roots and soft intertidal sediment.
  • Use exclusion zones and clearly marked access routes to prevent repeated crushing of mangrove margins and creek banks.
  • Prevent sediment plumes and rapid drainage from entering connected habitat.
  • Have a qualified aquatic fauna ecologist inspect fish trapped by cofferdams, trenches, culverts or dewatering.
  • Record fish observations, water conditions, capture locations and release locations so impacts can be assessed and managed.

Survey methodology: 1. Define and inspect aquatic habitat

Flatback Mangrovegoby is a small estuarine fish associated with mangroves, saltmarsh, shallow tidal channels and nearby freshwater reaches. The supplied documents do not provide a species-specific survey guideline or prescribed survey effort, so survey design must be set by a qualified aquatic ecologist for the site, tidal regime and proposed impact.

Map mangrove stands, saltmarsh, shallow tidal creeks, pools, soft mud and sand-mud substrate, organic debris, and channels close to freshwater inflow before selecting survey sites.

Prioritise sampling within the mangrove forest, where fish abundance can be higher than along the seaward edge or adjacent mudflat.

Include clear to slightly turbid shallow water in tidal estuaries, coastal river reaches, bays, inlets and coastal lagoons where these habitats occur.

Adult size: Up to 65 mm total length, usually to 50 mm.

Victorian distribution: Currently known from Westernport, including mangrove habitat close to freshwater inflow.

Survey methodology: 2. Targeted fish sampling

Use methods suitable for shallow tidal fish habitat, such as fine-mesh seine or pop-net sampling, baited or unbaited traps where lawful, and appropriately authorised electrofishing where site conditions and permits allow.

Sample representative mangrove-forest microhabitats as well as the seaward edge, adjacent mudflat, tidal channels and freshwater-influenced reaches, because abundance varies strongly among mangrove microhabitats.

Use replicate sampling stations and record the sampled area, water depth, tide, salinity, temperature, dissolved oxygen, turbidity, weather, method, mesh size, soak or sweep duration and catch per unit effort.

Survey methodology: 3. Timing and detection conditions

Schedule repeat sampling across the tidal cycle and across seasons where the construction program allows, rather than relying on one visit.

Give additional sampling priority to autumn and spring, when high abundance has been recorded in mangrove and saltmarsh habitat, while recognising that this evidence comes from Botany Bay in New South Wales and may not directly predict Westernport results.

Sample during suitable daylight or low-light conditions for the selected method, and avoid conditions that make safe or effective sampling impossible, including unsafe tides, excessive flow or poor access.

Measure dissolved oxygen because the species can tolerate low oxygen and may perform aquatic surface respiration below 0.9 g/L, which can affect where fish are observed.

Generation length: Projected at 3 years.

Recorded temperature tolerance: Recorded in water up to 27.5 degrees Celsius.

Salinity records: Recorded from fully marine conditions of about 56,000 microsiemens per centimetre to about 1,300 microsiemens per centimetre in a lower freshwater reach.

Survey methodology: Minimum effort and reporting

  • Prepare a site-specific effort statement before fieldwork because no prescribed number of nights, hours, trap nights, transect length or area is provided in the supplied documents.
  • Use the same stations and measurable effort on repeat visits so that non-detection can be distinguished from a change in sampling effort.
  • Record all captures, sightings, failed samples, environmental measurements, coordinates, photographs and habitat descriptions, including records of fish using surface respiration or remaining in shallow mangrove pools.
  • Have an aquatic ecologist identify uncertain goby specimens and retain voucher material only where authorised and necessary.
  • Submit confirmed records and negative survey results, with method and effort, to the relevant Victorian wildlife database and any other state database required by the approval or land manager.
  • Check current Victorian listing, permit and data-submission requirements before fieldwork because the supplied sources include historic and current database information.

Before habitat disturbance: Avoid and minimise

Treat mangrove, saltmarsh and shallow tidal water as potential habitat until an aquatic assessment shows otherwise. The species is restricted in Victoria and the assessment identifies habitat loss and water pollution as major risks.

Retain mangrove stands, saltmarsh, shallow tidal channels, soft mud and sand-mud substrate, organic debris and freshwater-influenced upper estuarine reaches.

Avoid isolating mangrove habitat from nearby tidal channels, saltmarsh or freshwater inflows, because the species uses these connected estuarine environments.

Keep machinery, stockpiles, access tracks, fuels and chemicals out of retained aquatic habitat and establish site-specific no-go areas before works start.

Prevent changes to tidal exchange, drainage, salinity, dissolved oxygen and sediment movement unless they have been assessed and approved.

Before habitat disturbance: Approvals and work planning

Check the current Victorian conservation listing and all permit requirements before clearing, dredging, bank works, dewatering or waterway crossings.

The species is not listed under the EPBC Act in the supplied project information, but the project officer must still complete the current EPBC Act protected-matters check and referral assessment where the action may affect a nationally protected matter.

Obtain advice from the relevant Victorian authority and waterway manager where works may affect Westernport or other tidal waters.

Prepare a fauna management plan covering aquatic survey results, exclusion areas, dewatering, fish rescue, water-quality controls, incident response, authorised handlers and reporting.

Stage works so that retained mangrove and tidal habitat remains connected while disturbed areas are restored or made safe.

Victorian status in supplied information: Endangered in the user-supplied listing; the assessment proposed Endangered in Victoria.

EPBC status in supplied information: Not listed.

Victorian concentration: The assessment identifies Westernport as the only current Victorian area known for the species.

Before habitat disturbance: Pre-clearance preparation

Complete targeted aquatic surveys before disturbance, including all mangrove habitat immediately downstream, upstream and adjacent to the work footprint where fish could move during tides or dewatering.

Mark mangrove retention areas, tidal channels, fish refuge pools, freshwater inflows, access limits and water-quality protection zones on plans and in the field.

Install exclusion fencing only where it will not block tidal flow or strand fish, and inspect it after tides, rain and earthworks.

Before isolation or dewatering, obtain an approved fish rescue and relocation method and confirm the authorised personnel, equipment, holding water and nearby receiving habitat.

During habitat disturbance: Daily controls and machinery coordination

Keep aquatic habitat wet, connected and free of avoidable sediment and contaminants during works. A fauna spotter catcher should work as part of the aquatic supervision team, not as a substitute for water-quality and tidal-flow controls.

Hold a pre-start briefing each day covering mapped habitat, exclusion areas, tide conditions, dewatering stages, machinery movements and the stop-work procedure.

The spotter catcher or aquatic ecologist must remain in communication with machine operators and direct plant away from retained mangroves, channels, refuge pools and unstable soft substrates.

Inspect exclusion fencing, silt controls, pumps, hoses, screens, bunds and access points before work and after heavy rain, high flows or tidal inundation.

Stop or modify work if fish are exposed, stranded, trapped, injured, present in an isolation zone, or if sediment, fuel, chemicals or contaminated water enter retained habitat.

During habitat disturbance: Fish rescue and handling

If a Flatback Mangrovegoby is found, stop the activity that could harm it and notify the authorised aquatic fauna handler and the site environmental officer.

Do not handle the fish unless authorised, trained and operating under the approved fauna management plan and relevant permit.

Keep handling time, air exposure, crowding and temperature change to a minimum, and use clean equipment and water from the capture location where appropriate to the approved method.

Relocate rescued fish only to nearby, suitable retained habitat with comparable tidal, salinity, temperature and dissolved-oxygen conditions, and only where the approved plan permits relocation.

Send injured or distressed fish to the nominated aquatic wildlife veterinarian or authorised wildlife carer, where such care is available and lawful.

During habitat disturbance: Habitat and water management

Maintain tidal connectivity and avoid leaving fish stranded in isolated pools, trenches, culverts, pump sumps or dewatered channels.

Use screened pump intakes and inspect them regularly to prevent fish entrainment, and progressively inspect the work area as water levels fall.

Protect mangrove roots, soft substrates, organic debris and shallow refuge areas from unnecessary removal or compaction.

Control turbid water, chemical spills, concrete washout, fuel leaks and other pollutants because water pollution and chemical spills are identified threats to this species.

During habitat disturbance: Records and incident triggers

  • Record every capture, observation, mortality, injury, relocation and non-target aquatic fauna event with date, time, coordinates, tide, water conditions, habitat, action taken and the names of authorised personnel.
  • Record the number of fish, approximate size, photographs where practical, capture method, holding time, release location and release condition.
  • Stop work and escalate to the project environmental officer if the species is found outside the approved impact area, if the approved relocation habitat is unavailable, or if the fauna management plan cannot be followed.
  • Report deaths, significant injuries, pollution events, stranding and unexpected habitat impacts to the approval holder and relevant regulator within the timeframe set by the approval.

After habitat disturbance: Immediate checks

Post-work checks should confirm that fish were not stranded or trapped and that retained Westernport or estuarine habitat remains functional. Monitoring should focus on the habitat features identified in the pre-work assessment.

Inspect the full work area, pumps, sumps, trenches, culverts, temporary dams and isolated pools after each dewatering or tidal reconnection event.

Complete a final aquatic fauna check before removing screens, bunds, exclusion fencing or other controls that could trap fish.

Check mangrove edges, shallow channels and freshwater-influenced reaches for stranded fish, dead fish, oil, sediment deposits, altered flow paths and blocked tidal connections.

Do not remove temporary controls until the aquatic ecologist or authorised environmental officer confirms that the area is safe for fish movement.

After habitat disturbance: Monitoring and reporting

Repeat the agreed fish sampling at retained and restored habitat using the same stations, methods and effort used before works.

Compare catch rates, species presence, water quality, mangrove condition and habitat connectivity with the pre-work baseline, while accounting for seasonal and tidal variation.

Report confirmed records, mortalities, incidents, rehabilitation actions, monitoring results and any permit non-compliance to the project proponent and relevant Victorian database or regulator.

Maintain erosion, sediment, spill and exclusion controls until the site is stable and the approved completion criteria are met.

After habitat disturbance: Offsets and residual impacts

Check the approval and current Victorian offset requirements where impacts to mapped Flatback Mangrovegoby habitat remain after avoidance and mitigation.

Do not treat an offset as permission to remove mangrove or tidal habitat where the impact can be avoided.

For Victorian native vegetation applications, confirm whether the current mapping and assessment generate a species offset, because a supplied 2022 scenario report identified mapped Flatback Mangrovegoby habitat and a species offset requirement.

Example supplied scenario: The 2022 Victorian scenario report calculated 0.194 species units for Flatback Mangrovegoby habitat.

Example mapped habitat impact: The same scenario report identified 0.4986 percent of mapped habitat value affected.

Rehabilitation actions: Restore habitat structure and connection

Rehabilitation should recreate shallow, connected estuarine habitat rather than only revegetating the terrestrial margin. The target is functioning mangrove and saltmarsh habitat with suitable water movement, substrate and water quality.

Re-establish tidal exchange and shallow-water connectivity to retained mangrove, saltmarsh and freshwater-influenced channels.

Use local provenance mangrove and saltmarsh species suited to the site, including Grey Mangrove, Avicennia marina, where appropriate to the existing community and approvals.

Reinstate soft mud or sand-mud substrate and retain suitable organic debris where it will not obstruct fish passage or create a pollution risk.

Remove temporary barriers, redundant hardstand and compacted access surfaces where their removal will restore shallow tidal habitat without causing erosion.

Rehabilitation actions: Water quality and threat control

Design rehabilitation to maintain suitable salinity, dissolved oxygen, temperature, depth and flow across tidal and freshwater-influenced areas.

Control sediment, nutrients, hydrocarbons, chemicals, weeds and contaminated runoff during establishment and maintenance.

Inspect for blocked channels, fish stranding points, erosion, excessive sediment deposition and invasive plants after rainfall and high tides.

Do not introduce structures, woody debris or rock that reduce tidal exchange, create fish traps or alter the mangrove channel network without aquatic design review.

Rehabilitation actions: Monitoring and success measures

Monitor mangrove and saltmarsh establishment, channel connectivity, substrate stability, water quality, fish access and Flatback Mangrovegoby use at agreed intervals and across more than one season.

Use repeat aquatic sampling at restored and reference sites, with consistent stations and recorded effort, rather than relying only on visual inspection.

Set completion criteria that include functioning tidal connections, no persistent fish-stranding points, stable banks and substrate, established local mangrove or saltmarsh cover, and confirmed use by the target fish where monitoring conditions allow.

Continue weed, erosion, sediment and pollution controls until the site meets the approved completion criteria, and submit monitoring results and confirmed records to the relevant Victorian wildlife database.

Sources