Tim Pankhurst, Seafood magazine, December 2022

Net sounder technology ban under review

A ban on new technology that increases trawl efficiency and reduces environmental impacts is under review.

Deepwater Group chief executive Aaron Irving argues net sounder review is widely supported and long overdue. (image Steve Hussey)

Fisheries New Zealand (FNZ) has called for submissions on a proposal to revoke the prohibition on the use of net sonde cables that is seen as outdated and outmoded by the deepwater sector.

Deepwater Group (DWG) Chief Executive Aaron Irving says there is wide support for the proposal.  DWG represents 45 quota-holding seafood companies that operate more than 60 commercial deepwater vessels and employ approximately 8,500 people.

“New Zealand is the only fishing nation where the use of enhanced trawl sonar equipment is prohibited,” Irving says. “This is equipment that allows fishers to see the seabed ahead of them as they fish for the healthy protein that people rely on commercial fishers to catch, such as hoki, orange roughy and southern blue whiting.

“There were legitimate reasons for this 40 years ago, particularly in regard to the white-capped albatross population, but there are now long-standing, proven protections in place.

“Bird streamers or tori lines, bafflers and other measures have markedly reduced the probability of encountering bird strikes when using trawl gear and have made the reintroduction of this technology possible.”

“We welcome a review by the regulator, Fisheries New Zealand, of this regulation, which inhibits more efficient harvesting.”

This anomaly has been acknowledged by FNZ, who describe in their proposal what commercial fishers have been saying for a long time – that this is a missed opportunity for sustainable fishing practice, and that fishers are already using, or are prepared to use, the methods that mitigate any risk associated with the cable.

The cable under review acts as a third wire in addition to the two wires attached to either end of the trawl and relays a live video feed on the position of the net and the trawl doors in relation to the surface and the seafloor, the position and movement of fish schools ahead and the quantum of fish entering the cod end.

“Three oft-raised concerns are impacts on protected species, carbon emissions and loss of fishing gear,” Irving says.

“Reducing the number of trawl events, their duration and the precision with which the gear can be directed will all impact positively on reducing these causes of concern.

“Put simply, better equipment allows us to catch the same amount of fish for people, as fixed under the Quota Management System, more quickly. It means we use less fuel and less energy and we spend less time interacting with the seafloor. Fishers can also come back home from sea sooner.”

There have been considerable advances in wireless technology used by the fishing sector but deepwater fishing remains challenging.

“The net may be a kilometre deep and a kilometre behind the vessel, but it may be pushed by currents and it may be skewed,” Irving says. “It’s a bit like landing an aeroplane on a windy narrow strip in the dark.

“A direct net sonde video link would reduce that uncertainty.

“If the gear is asymmetrical, then catch efficiency is compromised and there is an increased chance of unwanted catch.”

Furuno trawl sonar display showing the outline of net and fish school, as well as usual depth and water temperature.

The leap to trawl sonar is like seeing the whole view through a car’s windscreen, rather than through the rear-vision mirror.

This is especially relevant to the New Zealand deepwater fleet which generally fishes in much deeper waters, 600 to 1000 metres, compared with the usual 400 to 600 metre range of northern fisheries.

Wesmar trawl sonar display showing trawl doors in relation to school of fish and fish school in net.

The development of broad beam multifrequency transducers coupled with video and laser measuring enables differentiation of a school’s acoustic signal and calculation of the biomass of each segment, the DWG said in its FNZ submission. This real time delivery through a fixed cable allows far more certainty in the biomass estimates than from single-frequency hull-mounted acoustic surveys, especially where there are mixed species issues, or when aeration under the hull in poor weather affects signals.

Net sondes were developed and went into commercial use in the 1950s following the development of hydroacoustic technology (SONAR) during World War Two. Their popularity with the German fleet targeting pelagics such as herring and mackerel is the source of the net sonde term – net sounder in English.

The technology has since taken another leap forward and net sondes have become trawl sonars that have hugely increased information gathering and provision capabilities.

Irving says the proposal is widely supported.

“The call was made more than a year ago by the Prime Minister’s Chief Science Advisor, Dame Juliet Gerrard,  who, in her March 2021 report on the future of commercial fishing, recommended reducing barriers to innovation and empowering fishers to innovate and improve environmental outcomes.”

Crown research institute Plant and Food Research also supports the technology.

“While the broader context needs to be considered, enabling power and high-speed data transmission through a third wire from the trawl supports the development of real time high-resolution imaging and data gathering technologies,” says Mark Jarvis, business manager of seafood technologies.

“Such capability would open the door to systems that enable greater by-catch reduction and effective bottom contact measuring and monitoring.

“At the same time, this new technology would reduce the hazards to fishers associated with unexpectedly large catches and enable a range of operational practices that increase fishing efficiency while providing reliable data to support the reduction of environmental impacts”.

If, or once, the technology is approved, its takeup is voluntary.

Systems are expensive, as much as $500,000, and will have the greatest application in deep water.

Two cable types are used, copper and fibre optic, with the former being more robust and able to be repaired.

The cables are subject to abrasion and bending and shear forces in such a robust environment and need to be configured in harmony with the net.

Fisheries consultant and longtime endangered species advocate Richard Wells says “when the regulation is revoked, DWG will look to support any deepwater vessels considering equipping with apparatus that needs a data transmission cable to ensure the best mitigation of seabird risk.

“This model, applied in conjunction with FNZ for over a decade, is practical and provides good results.”

Seabird warp captures have been reduced by 75 percent since the DWG’s formation in 2006. This is most marked in the squid fishery, which is the highest-risk fishery, and also the most highly observed and documented.