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10 February 2021 5 min read

Capturing soundwaves underwater can reveal how many fish there are

Hello darkness, my old friend. It’s not the sound of silence being used by our researchers to monitor marine life beneath the waves; but the recording of sound to estimate how many fish there are, and monitor changes in the marine environment.

The technology is so acute it can even be used to detect fish eggs, plankton and gas bubbles!

Diving deep into acoustics  

Dr Ben Scoulding is a fisheries acoustics and optics researcher who records and assesses the transmission and reception of sound waves for the monitoring of resources in the water column and on the seafloor – from marine life to even non-living things, such as gas and oil.  

Similar to a recreational fish finder, wuse echosounders which convert electrical energy into sound energyTogether with trawls or other biological samplers we use calibrated echosounders to study marine fauna and provide estimates of fish abundance to tune population assessments,” Scoulding explains.  

The information can assist fisheries managers in setting sustainable levels of fishing catch."

Acoustic applications are vast, like our oceans

Acoustics research has an incredibly broad range of applications. It can record information from oil droplets to larger marine species, such as tuna and sharks.

“We can use acoustics for tracking the migration of fish up rivers, interactions between predator and prey, the ecology and behaviour of aquatic communities, and monitoring fish in aquaculture,” Scoulding says.

“Acoustics helps us describe biological and physical features within aquatic systems and monitor variability in the marine environment.

“We can also use it to detect underwater gas seeps and apply it for baseline studies to track trends over time and space for large ocean basins.

Hydroacoustic methods provide one of the most cost-effective means for sampling the aquatic environment. Compared to light or radio waves, soundwaves propagate well in water and can reflect off targets of interest.

It also captures continuous recordings over large parts of the water column; and isn’t limited by things such as light, turbidity, and other environmental factors, which can negatively influence other sampling methods.

A snappy and sound research approach

Fisheries and aquaculture are important industries in Australia, both economically and socially. 

Acoustics and optical technologies supported a recent abundance survey of snapper (Chrysophrys auratus) near Bernier Island in Western Australia (WA). The survey was funded by the Fisheries Research and Development Corporation and was a collaboration between CSIRO and the Department of Primary Industries and Regional Development 

Researchers combined acoustics technology with cameras to verify observations.

Snapper are an important commercial and recreational species in WA. The most recent assessment results indicated that the stock was around 20 per cent of the unfished spawning biomass, which resulted in a closure to protect key spawning aggregations,” Scoulding reveals. 

Our survey aimed to provide industry, scientists and fishery managers with an evaluation of the use of acoustic methods for monitoring the distribution and abundance of snapper in spawning aggregations.  

“It was the first acoustic survey of reef-aggregating fish in Australia. It was also the first example anywhere of using unbaited Remote Underwater Videos to verify active-acoustic observations. 

Using cameras, we targeted different fish schools seen by the acoustics to confirm what the schools were.  

“The survey showed the potential of this technology to better manage our marine resources.” 

Sustainability of orange roughy 

Orange roughy, a deep-sea fish, was first discovered in Australia in the 1970sand widespread commercial fishing of the species was quickly established. As orange roughy is long lived, late to mature and has fewer juveniles joining the adult population each year, recovery from overfishing has been slow with significant depletion of stocks.  

High-precision and cost-effective monitoring methods to assess stock levels of orange roughy is vital to ensure sustainable management of the species. We apply this research for orange roughy in both Australian and New Zealand waters. 

Historically, orange roughy was significantly overfished. Acoustics research is vital for sustainable management of the species.

“Our approach reduces sampling errors and improves data collected by fishing vessels. It will inform industry surveys for improved stock assessment and help achieve Marine Stewardship Council (MSC) certification,” Scoulding says.

Improving orange roughy abundance estimates will ultimately help deliver jobs and growth, food security and adherence to fishery obligations. 

Acoustics research is also used to assess stocks of blue grenadier.  

Long-term observation 

Along with being used for fish abundanceacoustics research is also helping us better understand mid-water preyknown collectively as micronekton. 

“Micronekton play an important part in the ocean food web as they transfer energy from primary producers at the ocean surface to top predators such as tunas, billfish, sharks, seals and seabirds,” Scoulding says.  

“The mass and distribution of micronekton reflects broad-scale patterns in the structure and function of the ocean, as well as the dynamics of marine ecosystems. But knowledge on micronekton in the Southern Hemisphere is limited.  

“We’re working to increase scientific knowledge about micronekton. This includes how species are distributed, such as small fish, squid, krill and jellyfish. 

Understanding how and where marine species are distributed is providing our scientists with new insights on ocean functionality.

Acoustic mapping complements established observing systems such as physical sampling of ocean currents, surveys of ocean chemistry and biology (plankton and zooplankton), and electronic tagging and tracking of large marine fish and mammals. 

“Acoustic technology greatly enhances our capability to monitor shifts in food availabilitymodelling of oceanography, the impact of fisheries on climate change and understanding the behaviour of top predators. This is critical for long-term observations and healthy oceans,” Scoulding concludes. 

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