Barriers to fish passage

Australian native fish require unimpeded access along waterways in order to survive and reproduce. Both fresh and saltwater fish move within waters at different times to access food and shelter, to avoid predators, and to seek out mates. Of the 83 species of freshwater fish in south eastern Australia, over half migrate at least once as part of their life cycle. Some species can migrate thousands of kilometres while others only move a short distance.

Barriers to fish passage prevent the migration of native fish species and can have severe implications for these populations. In extreme cases, barriers can result in localised extinctions. This has occurred for Golden Perch populations above several large weirs and dams.

Types of barriers

Barriers can be:

• physical structures (e.g. weirs, dams, causeways and floodgates)
• hydraulic (e.g. areas of high velocity flow or turbulence)
• chemical (e.g. pollution plumes, acid sulfate soil discharge and low dissolved oxygen slugs)
• behavioural obstructions (e.g. dark tunnels or unnatural substrates created by pipes).

Habitats where food and shelter are degraded may also impact upon the migration of native fish species.

Fish passage barriers can adversely impact native fish by:

• interrupting spawning or seasonal migrations
• restricting access to preferred habitat and food resources
• increasing the chance of predation and disease
• reducing genetic flow between populations through population fragmentation.

The cumulative effect of barriers to fish passage has been identified in NSW as a Key Threatening Process under the Fisheries Management Act 1994 as the installation and operation of instream structures threatens the survival of native fish.