HUNDREDS OF BARRIERS IMPEDING FISH MOVEMENT

24 JUNE 2022

Can a small fish make its way up the rivers and tributaries in the Lower Barron, Mossman and Daintree catchments? That’s the basis for a project that’s assessing if infrastructure like weirs, dams and culverts are stopping fish moving upstream to nursery and breeding grounds.

These river catchments are hotspots for diadromous fish species like barramundi and jungle perch – adults spawn in estuaries and juvenile fish migrate upstream to freshwater habitat where they mature into adults.

More than 1600 potential barriers have been identified as part of a new project aiming to improve recreational fishing outcomes by improving waterway habitat connection.

Terrain NRM’s Lana Hepburn explains that a number of factors determine which barriers would be most beneficial to remediate to get good recreational fishing and ecological outcomes.

“The goal is to open as much habitat upstream as we can, so we look at where the barrier is in the catchment. If it’s closer to the coast it’s potentially blocking more upstream habitat – so the distance between each barrier is important too.

“We also look at how connected a waterway is to the ocean. Barriers in rivers that connect to the ocean would be prioritised over small tributaries that flow into different creeks and rivers before hitting the ocean,” Lana said.

Some barriers are only obvious in low flow conditions during winter, but fish need to be able to migrate at different times of the year.

A field team from Terrain NRM, Wet Tropics Waterways and Dawul Wuru Aboriginal Corporation’s Yirrganydji Land & Sea Rangers have now physically inspected hundreds of barriers to assess their priority for remediation.

Terrain NRM car at creek causeway

“There’s only so much you can learn from geospatial mapping and aerial photography, which is how we identify the potential barriers, and then we need to get out and ‘groundtruth’ them,” said Lana.

“When we’re talking about barriers, a lot can stand in the way of fish! When they migrate upstream they are just small fingerlings and no bigger than a few centimetres, so you can see how their movement could be impeded.

“Causeways, crossings and culverts can all create drops that act like mini waterfalls which they can’t get past. Narrow pipes can also cause water to flow so fast they can’t swim upstream through it.”

The findings will be shared with groups around the region who also have an interest in improving fish habitat connectivity.

The “Connecting Wet Tropics Waterways for Sustainable Recreational Fishing” project is funded by Terrain NRM through the Australian Government’s Fisheries Habitat Restoration Program.

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