AUSTEn project PhD student Constantin Scherelis is using hydroacoustics to help understand how fish behave in the strong currents of high-potential tidal energy sites.
It’s the first step towards estimating and minimising the impact of future tidal arrays on marine life.
Understanding environmental impact of tidal energy is a crucial step towards gaining the necessary public support and regulatory approval for future commercial-scale tidal arrays.
One important concern is proving the low impact of devices on fish and marine mammals. This first requires an understanding of how fish currently behave at potential tidal energy sites — information that can also help tidal energy developers design and deploy low-impact arrays.
Scherelis uses hydroacoustics to gather this information on fish behaviour at the AUSTEn project’s two tidal energy sites: the Banks Strait, Tasmania, and the Clarence Strait, Darwin.
“I study the biophysical linkages, which means I look at what’s happening between the marine life and the currents to get an idea of how much biomass is in the water column, where it is and how it behaves,” Scherelis said.
He uses underwater remote sensors to gather data from the ocean’s depths, relying on instruments that measure currents and sample biomass.
During the 2018 Banks Strait campaign, two moorings were deployed for a period of three months: an ADCP that measures currents and an AZFP that samples biomass in the water column.
“Both emit an acoustic wave at a certain frequency. Based on the amount of backscatter — energy that’s returned to the transducer — we can make inferences about the fish in the water column; the number, where they are, and what size they might be.”
Initial findings from the Banks Strait show a big difference between the abundance and spatial distribution of fish during the day and at night, explains Scherelis.
“At night, the fish were significantly more active. Overall, we also saw a slight preference for depths between 20-40m.
“We also found elevated backscatter during faster currents. If we can show this correlation is biological in nature and statistically significant, it will be an important consideration for tidal energy developers.”
During the 2019 Clarence Strait campaign, a new-generation ADCP was deployed to concurrently sample currents and biomass. The device will be in the water for three months, sampling four times per second.
With this data, Scherelis hopes to demonstrate not just how much biomass is present and how it is distributed, but also how fish behaviour changes over natural cycles, such as day and night or season to season.
Back at the Australian Maritime College, Scherelis process the hydroacoustic data using custom Matlab code as well as dedicated software for biomass interpretation called Echoview.
Along with his AUSTEn project colleagues, Scherelis sees a bright future for tidal energy.
“Many nations are moving towards sustainable energy sources, and I think tidal energy has an important role to play in meeting our energy needs.
“One of the key reasons for the shift to renewables is obviously environmental, and so being sure that the practices we perform are indeed as sustainable and as low-impact as we hope is important to verify.”