Monitoring orange roughy fish stocks

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[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.

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

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

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

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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.

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