Removing ‘fish barriers’

Removing ‘fish barriers’ to reconnect waterway highways

From thick aquatic weeds to fast-flowing drains, fish barriers are stopping fish from migrating between freshwater and marine habitats. This loss of connectivity is contributing to a decline in fish diversity in some freshwater systems in the Great Barrier Reef catchments.

Scientists say there are thousands of fish barriers in catchments along the Great Barrier Reef and reconnecting these waterways is an important step to improving the health of rivers and estuarine environments.

TropWATER scientists are using underwater drop cameras and boat mounted electro-fishing surveys to identify what fish barriers are having the most impact in high priority streams.

The data gives local management groups the best understanding of what streams take priority to be reconnected.

What are fish barriers?

A fish barrier is anything that stops a fish from moving upstream or downstream – it can be a physical barrier or a chemical barrier.

Human-made physical barriers like culverts, weirs, causeways and tidal gates are common and have increased from urban and agricultural development activities across our floodplains. These barriers may completely block water, or the water may be flowing but fish are unable to travel because the water is too shallow, too swift or too steep.

Barriers are not always physical. Chemical barriers occur when the water quality has become so poor there’s simply not enough oxygen for the fish to swim through.

Aquatic weeds, like hymenachne, are known to build up to create a physical barrier by blocking easy passage, but also become a chemical barrier because of the weed reducing oxygen levels.

Why do fish travel?

Many fish species need to move between marine and freshwater habitats at different times of the year to feed, reproduce, spawn, access nursery grounds, escape predators and more.

Some of our most iconic fish need to migrate, including mangrove jack, barramundi, longfin eel, and, jungle perch, among several other species.

Without the ability to move between freshwater and marine habitats, these species will not be able to complete their lifecycle ecology, potentially leaving fewer of these fish in our waters.

Where have scientists surveyed?

The freshwater research team have surveyed high priority streams in the Wet Tropics and the Burdekin floodplain. Working with local natural resource management groups, scientists are able to make recommendations for barrier removal. Investment in removing barriers to fish movement is critical but more work is needed to restore our floodplains back towards productive systems more similar to how they were in the past.


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