In coastal catchments connectivity between freshwater and saltwater habitats is particularly important as diadromous fish often comprise a high proportion of coastal freshwater fish communities. In tropical and subtropical regions of eastern Australia many diadromous species have high socio-economic value, forming the basis of key fisheries. This is in addition to the vital ecological roles diadromous species fulfil in maintaining functional ecosystems.
Growing recognition within the state of Queensland of the migratory requirements of diadromous species, combined with recent adoption of ecosystem health reporting, has seen Local Governments, Natural Resource Managers, Catchment Management Authorities and community groups eager to remediate barriers to fish passage. However, the cost associated with fishways, particularly technical type fishways, often prohibits organisations from undertaking fish passage projects.
Rock ramp fishways present an effective, low cost fish passage option when compared to technical fishway designs such as vertical-slot or lock fishways. Rock ramps are generally based on a pool/ridge configuration and are designed to emulate natural riffles. Key features include the irregularity of rock faces, ridge spaces of 1.5 – 3.0 m, ridge drops of 50 – 75 mm and minimum pool depths of 300 mm. These features have been incorporated in full and partial width designs to good effect. Recent monitoring observation in central Queensland have recorded up to 31,000 fish/day successfully ascending this type of fishway, with the majority of the catch comprising small bodied and juvenile fish, <50 mm in length. It is thought that the surface roughness and the dissipative capacity of the deeper pools creates conditions conducive to the passage of small fish.
Here we present case studies of four rock ramp fishways constructed in tropical and subtropical coastal systems, on barriers ranging from 0.45 – 2.4 m in height. Case studies detail the design, construction and monitoring of each fishway.