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.
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.
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.