Not all fish can “just keep swimming” - barriers may block their journey.
Several fish species need access to both fresh and marine waters throughout their lives. Unfortunately, barriers like weirs, dams, road crossings and even rail networks, can end their journey earlier than planned.
“Take the iconic barramundi,” explains Shreyash G Bhandary, an intern with the Healthy Waters Partnership. “Young barra love to hang out in freshwater, but once they reach sexual maturity, they need to swim downstream to estuarine areas, where rivers meet the sea.
“Estuarine mudflats provide the perfect temperature and salinity levels for barramundi to spawn. Saltwater is essential for them; their eggs and larvae cannot survive without it. Plus, it triggers the transformation of male barramundi into females."
“Barramundi really need access to both fresh and saltwater to thrive. Fish barriers inhibit their movement and are a sign of habitat fragmentation,” he adds.
Shreyash, who is completing his master’s in marine biology at James Cook University, has mapped potential fish barriers in the Townsville Dry Tropics region during his internship.
Scaling-up data
The Technical Report, which dives into the data collation and analysis behind the Partnership’s yearly Waterways Report Card, includes an indicator category for ‘fish barriers.’
“We track how many fish barriers can be crossed and how many can’t in the Townsville Dry Tropics region, along with the length of river each barrier affects,” says Adam Shand, Environmental Data Analyst for the Healthy Waters Partnership.
“Shreyash’s work will give our existing data a boost, as it hasn’t been updated since fish barriers were first included in the 2020 Waterways Report Card.
“We expect to discover several new barriers in the Black Basin, where none are currently documented.”
The technical backbone
The same way there are different languages in the world, there are also many computer programming languages. Adam developed three scripts, each with its own role in the project, using R programming.
“You can think of a script as a recipe for the computer to follow,” said Adam.
“The first script whipped up a detailed map of the region’s waterways. The next one helped us find potential road and rail barriers along the river network, and the final script ranked those barriers based on how much they could restrict fish movement.”
After pinpointing and prioritising the fish barriers, Shreyash took the data and conducted a visual assessment using satellite imagery for further validation.
“This involved using QGIS to take a closer look at the mapping results and classify each barrier using a flowchart we developed,” explains Shreyash.
“Then we cross-referenced everything with Queensland Globe to get high-resolution imagery for even better accuracy.”
The score for ‘fish barriers’ is calculated by looking at barrier density (kilometres of river per barrier, both passable and impassable), the percentage of stream length to the first barrier, and the percentage of stream to the first impassable barrier.
The data plays a part in the ‘habitat and hydrology’ grade in the Report Card.
Casting a wider career net
“Completing the fish mapping project, knowing it will be included in the Technical Report and contribute to the Report Card’s habitat and hydrology grade, was a significant highlight for me during my internship,” says Shreyash.
The internship also offered a fantastic opportunity for Shreyash to cast his net wider, gaining industry exposure and honing his science communication skills. Through his internship, he’s also been out with our partner and host Port of Townsville to participate in groundwater and biosecurity monitoring, and Wildlife Surrounds to learn riparian vegetation assessment methods.
“My internship has been an eye-opening experience, giving me hands-on exposure to various Partners and their fieldwork activities. The mix of office work and field studies has been particularly rewarding.
“As I continue my journey of becoming an environmental consultant or scientist, I carry forward the invaluable insights into what working in the environmental sector entails.”
