Fish Barrier Prioritisation (Wetland/Offstream)

The objective of the wetland/offstream barrier prioritisation is to identify and assess anthropogenic physical barriers (biophysical, such as weed chokes, are not considered) that prevent, delay or obstruct fish migration in coastal catchments. Fish barriers identified through this process are ranked in order of priority, accounting for the cumulative impacts barriers have on the environment, fisheries resources and the economy. Social, economic and fisheries productivity benefits of barrier remediation are also considered. This method prioritises freshwater (lacustrine and palustrine) wetland barriers.

This method prioritises wetland barriers from most important through to the least important based on the biological, social and economic benefits and the difficulty and cost of remediation. It ignores the presence of existing fishways on any wetland barrier as there is limited information on the success of these structures. Species likely to be accessing wetland habitats as a part of their life cycle were identified.

The wetland fish barrier prioritisation method systematically identifies all potential physical barriers to fish passage into offstream wetlands (lacustrine and palustrine) in a study area. A holistic prioritisation process is used to objectively choose barriers to remediate to obtain the greatest benefits, and the top ranked barriers in the study areas have remediation options costed. This holistic process assists decision makers in determining where to best allocate funding opportunities to ensure the greatest environmental and socioeconomic outcomes for the study area.

The assessment incorporates the area of wetland, catchment, wetland permanence and barrier location in the first stage. The second stage incorporates an assessment of wetland condition, stream flow, wetland fish habitat and barrier types. The third stage incorporates an assessment of social, economic and fisheries productivity as well as restoration costs and viability.

The opportunity exists to update the assessment of barriers based on new information and any remediation or fishway works that may have been installed.

Barriers to fish passage such as dams, weirs, causeways, culverts, earthen bunds and floodgates can impact the health of aquatic systems by altering natural flow regimes, and causing impassable barriers to aquatic fauna, especially fish. Many high value fish species require unimpeded access between habitats (i.e. between inland freshwater habitats and estuarine/marine habitats). Wetlands in coastal regions can be modified through the construction of barriers or bunds, raising the normal water level of the wetland.

Freshwater wetland habitats are important environments for fish and are used by a wide range of fish species. Coastal wetlands (lacustrine and palustrine) are important for juveniles of many diadromous fish species as they provide predator free, food rich, nursery habitats outside the estuarine environment. Fish undertake migrations into lowland wetland habitats as part of their complex life-long migration strategies that see many species utilising estuarine and freshwater wetlands (lacustrine and palustrine), small freshwater streams and large freshwater stream habitats at various stages of their life cycle.

This method’s objective is to identify and assess physical anthropogenic barriers that prevent, delay or obstruct fish migration to/from and in freshwater wetlands. Fish barriers identified through this process are ranked in order of priority, accounting for the cumulative impacts’ barriers have on the environment, fisheries resources, economy and local community. The ultimate aim is to remediate barriers preventing connectivity, and this method assists decision makers in choosing which barriers to focus on, as in many catchments there are large numbers of barriers which outweigh the resources available to remediate.

This method identifies and prioritises barriers through 3 major stages:

Stage 1. Remote assessment

The first stage systematically identifies all potential fish passage barriers on all wetlands (using QLD wetlands mapping) in the study area. This is done through catchment-scale GIS analysis of wetland characteristics and existing barriers.

Stage 2 – Field assessment

The second stage performs a site specific barrier assessment to validate, score and rank priority barriers against a further four metrics (barrier type, wetland condition, stream flow, wetland fish habitat).

Stage 3 – Socio-economic assessment

The third stage further refines and prioritises barriers based on economic, social and fisheries productivity criteria (fisheries importance, restoration cost, constructability).

The top ranked fish barriers, depending on the area are listed with remediation options and indicative costs. Importantly, this stage considers the net benefits of improving connectivity versus the economic cost of remediation. Barriers that can be remediated with low cost fishways while increasing fisheries productivity or restoring vulnerable fish species score high, whereas barriers requiring technical and expensive fishways score lower.

Remote (Risk) Assessment

• Area of wetland (largest = higher score)
• Catchment condition (higher vegetation cover = higher score)
• Barriers downstream from barrier (low to no barriers = higher score)
• Total area upstream to next barrier (larger upstream area = higher score)
• Wetland permanence (maintain water longer = higher score)
• Wetland elevation (lower elevation = higher score)
• Wetland size (larger wetland = higher score)
• Water permanence/refuge potential (expansive permanent water = higher score)

Field Assessment/Biological Assessment

• Barrier type (transparency/size, bigger = higher score)
• Wetland condition, (good condition, natural = higher score)
• Stream flow (higher outflow = higher score)
• Wetland fish habitat (higher habitat suitable for migratory fish = high score)

Social and Economic Assessment

• Fisheries importance
• Restoration cost
• Constructability
• Restoration effectiveness
• Productivity benefits (commercial/recreation benefits)

• Physical and spatial data for barriers (i.e. bridges, culverts, road crossings, infrastructure)
• High quality imagery (satellite/drone)
• Water observations from space (for water permanence/refuge potential)
• Elevation data
• Wetland mapping (wetland area)
• Wetland water regime (permanency, water flow through the wetland)
• Barrier types
• Vegetation condition
• Fish species information  (habitat requirements, migratory fish requirements)
• Economic (fisheries) significance
• Barrier flow characteristics (height, passability)

Expert knowledge of aquatic fauna and ecology including life cycle and habitat requirements. Field assessment skills and GIS data analysis skills. Knowledge of fisheries in the study area. Knowledge of fish important to fisheries industries in the study area. Research skills to get baseline information about fish species in the study area.

• Geographic Information System for barrier identification and prioritisation
• Camera equipment and other field assessment tools
• High quality imagery
• Wetland mapping
• Species lists
• Spatial data

Stage 1 – Remote assessment: All potential physical barriers in the study area are identified and a dataset is produced with a unique geo-referenced identification number. A prioritised list for field assessment is produced.

Stage 2 – Field assessment: A list of physical barriers from refining the list is Stage 1. This list scores physical barriers according to wetland condition, type of barrier and fish habitat.

Stage 3 – Socio-economic assessment: A third list of physical barriers from refining the list in Stage 2. The final stage produces a list of priority barriers from the second stage further refined by a social and economic assessment (four metrics). This stage produces the final list of top wetland barriers to fish migration at wetlands in the study area. This list contains the stream name, barrier name, barrier type, comments on the barrier and recommended remediation solution.

• Input into investment strategies for fish barrier remediation works in wetlands (offstream)
• Threat and risk identification
• Decision support
• Inform priorities of management interventions required to reduce risks to ecosystems from different threats and improve ecosystem condition

Designed for federal, state or local government agencies, water utilities, and natural resource management groups.

• Assesses one of the key threats to aquatic ecosystems – loss of connectivity to wetlands and offstream refuges
• Takes into account ecological, social and economic considerations
• Risk based approach allows for targeted prioritisation of barriers
• Informs management interventions at site scale despite being catchment scale assessment
• Repeated assessments can take into account changes in the catchment area and refine rankings
• Adaptive monitoring and management
• Considers the net benefits of improving connectivity versus the economic cost of remediation which provides workable and costed solutions for remediation

• Method applies to fish species only
• Instream habitat condition assessment plays a minor role in rankings and finer scale pressures may not be considered
• Focuses on migration and not all fish movement
• Conservation significance ranks common or abundant species low, common species may still be impacted by barriers to fish passage
• Individual scores for barriers not always provided in final report

2021 Fish Barrier Prioritisation – Mackay Whitsunday Region

Fitzroy Basin Association Fish Barrier Prioritisation Update 2019

This page should be cited as:

Department of Environment, Science and Innovation, Queensland (2021) Fish Barrier Prioritisation (Wetland/Offstream), WetlandInfo website, accessed 18 March 2024. Available at: https://wetlandinfo.des.qld.gov.au/wetlands/resources/tools/assessment-search-tool/fish-barrier-prioritisation-wetland-offstream/