Our tool for surveying deep-water fish stocks − developed with industry and deployed from fishing vessels − is proving an effective means of surveying orange roughy off eastern Tasmania.

The challenge

Managing recovering fisheries

Orange roughy are slow-growing, late-maturing, deep-sea fish that were overfished in Australia and New Zealand in the 1980s and 1990s, to the point that the fisheries collapsed and fish numbers became critically low. Numbers are now increasing in these fisheries, but to ensure their economic and environmental sustainability, we need to monitor these fish stocks closely.

Orange roughy being measured

Our response

High precision, low cost monitoring

We developed a high precision monitoring method that is low cost, uses available fishing methods, and in future will need minimal involvement of scientists. The survey tool, known as the net-attached acoustic optical system (AOS) is towed from a fishing vessel through schools of orange roughy to 'snapshot' winter-spawning populations.

The AOS measures the sound reflectance, or 'target strength' of fish at multiple frequencies − including an extra low frequency needed to identify orange roughy schools in some cases − while photographing fish with two cameras as they are herded into the trawl net. This allows for the acoustic frequency of the fish to be visually verified, so species identification and biomass estimates are more accurate than in the past. Laser markers provide a yardstick for fish measurement, and the net enables biological sampling to measure fish size and reproductive condition.

Attaching the AOS to the net enables acoustic, optical and biological sampling from one fishing vessel, rather than from two vessels (including a research vessel) as had been done previously. This greatly reduces the complexity and cost of the survey.

[Music plays and an image appears of wavy lines moving across a blue screen and the CSIRO logo appears in the bottom right corner]

[Animation image changes to show a view looking down on the RV Investigator on the ocean and the camera gradually pans around to show a view looking at the ship from underneath]

Narrator: In the past, accurate biomass measurement of deep water fish stock has been difficult.

[Animation image changes to show a circle of tiny dots in the sea and the camera zooms in]

Vessel based surveys using shipboard sounders are severely limited for deep water stocks which aggregate close to the seafloor. 

[Animation image shows circles of tiny dots moving down the screen from the top to the bottom and then the image changes to show a school of fish swimming]

Accurate determination of acoustic target strength for species being assessed is crucial  in calculating  biomass using acoustic methods.

[Animation image changes to show a model of the Acoustic Optical System spinning around and text appears: AOS, Acoustic Optical System]

To improve quality and efficiency of biomass assessments CSIRO, working in partnership with the fishing industry has developed the Acoustic Optical System, or AOS.

[Animation image changes to show a model of the Acoustic Optical System spinning in a clockwise direction and text appears beneath: Acoustic Optical System]

AOS can determine both the target strength of deep water species and their biomass quickly, accurately and economically.

[Animation image shows the camera zooming out to show the Acoustic Optical System attached to a trawl net]

AOS combines multi frequency  echo sounders and optical camera technologies in one self-contained platform, attached to the headline of a trawl net.

[Animation image shows the trawl net moving along beneath a grid pattern]

The system has been designed for routine use on commercial trawlers.

[Animation image shows model fish moving past the trawl net and the image shows tiny coloured dots moving around the school of fish]

For Biomass surveys AOS is deployed on the trawl net, towing the system in a grid pattern around 300 metres above the fish aggregations for up to ten hours.  The AOS archives the acoustic data which is later recovered on return to the ship.

[Animation image changes to show fish swimming along on the ocean floor past the camera and the image shows the trawl net moving over the fish]

The trawl net provides a very stable vehicle to carry AOS eliminating the effects of vessel motion. Close proximity of the AOS to the fish aggregations reduces beam spreading and absorption effects.

[Animation image shows the AOS being trawled along the ocean floor taking images of fish swimming in the ocean]

For target strength determination the AOS is deployed in bottom trawling mode to gather video and paired images of individual fish at close range.

[Animation image continues to show fish moving down the screen illuminating intermittently]

Acoustic data collected simultaneously ties together fish ID, size and orientation with reflected acoustic energy allowing accurate in-situ determination of target strength.

[Animation image changes to show fish moving backwards past the trawl net and the AOS model]

Fish collected in the trawl net provide information on reproductive condition and size distribution which further improves biomass assessment accuracy.

[Animation image changes to show the RV Investigator and the camera pans in a clockwise direction around the boat]

The AOS  has been in use reliably for assessment since 2010, helping to gain a better insight into stocks of Orange Roughy in the challenging seas around Tasmania and New Zealand.

[Animation image changes to show a close view of the model AOS and text appears: AOS, Acoustic Optical System]

More frequent and accurate assessments improve management and allow optimisation of harvests, improving sustainability and generating social licence.

[New text appears beneath: www.csiro.au/en/Research/OandA]

To find out more about CSIRO research visit www.csiro.au/en/Research/OandA.

 

AOS Orange Roughy

The results

Science-based monitoring in the hands of the fishing industry

The tool's success marks a major advance in the development of survey systems that require minimal infrastructure and place science-based monitoring in the hands of the fishing industry.

The AOS has been used to survey orange roughy in the fishery off eastern Tasmania. The survey information is used by the Australian Fisheries Management Authority to monitor the rebuilding of orange roughy stocks.

The system also has been used to survey orange roughy stocks in New Zealand, and blue grenadier stocks off western Tasmania. And there is overseas in interest from North America and Norway.

The ultimate aim is to develop systems that can be deployed and serviced by trained deck crew on commercial fishing vessels. This would prove invaluable for low value and high seas fisheries.

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