Fish movement and passage

Most native Queensland fish need to move along waterways to:

• breed
• return from spawning grounds or to access nursery areas
• access food in different habitats
• find shelter
• spread upstream
• find waterholes for drought refuge.

Fish movement occurs within and between inland rivers and creeks and along coastal streams throughout adult, juvenile and larval stages.

Delays or blockages, such as a waterway barrier, can seriously impact long-term survival and productivity of native fish species, and reduce their populations.

During floods and dry conditions

Many of Queensland's waterways are dry at times and subject to ephemeral flows, usually during the wet season from November to April. If conditions are dry, fish have limited opportunities to move.

Freshwater fish species need to move between waterways during flood times, particularly in the period after the peak of the flood.

This movement helps the fish:

• repopulate areas after drought
• return upstream after being washed downstream during floods.
• create genetic variability between streams to prevent inbreeding
• complete spawning migrations
• access opportune food sources.

Risks of restricted movement

Prior to the regulation of  waterway barrier works, many structures such as dams, weirs, floodgates and culverts were built on waterways in Queensland without consideration of fish passage.

Other waterways have been filled with soil or other materials, resulting in fragmented fish habitats in some locations. In many cases, fish are unable to move into waters upstream or downstream of these barriers.

This loss of access to habitat has caused a decline in distribution of native fish populations, including species of commercial, recreational and traditional importance such as barramundi, mullet and Australian bass.

In Australia, declines of inland species such as Murray cod, freshwater catfish and silver perch are thought to be largely due to the impacts of barriers to fish movement.