Integrated weighted longlines are not just a silver bullet for reducing seabird deaths, according to Malcolm McNeill, longline manager for Sealord, Nelson.
The device is so good at catching fish instead of seabirds, it is on track to be the golden bullet.
"Integrated weighted line, in my mind, is the closest thing in our fishery to the golden mitigation device," McNeill says.
The technology has inbuilt lead beads in each individual strand of Swivelline and requires no external attachments to gear or fishing methods. And because the weight distribution is constant, the sink rate has a lineal profile.
Two years of testing has highlighted the source of the gold. Not only is integrated weighted line extremely effective in reducing incidental seabird mortality (extensive trials in high-risk areas show reductions of more than 90 per cent), it manhandles well during fishing operations, reduces the workload of manual line weighting, and catches more target fish species.
"Though it does have a higher cost, in the toothfish fishery it catches more of the target species than a manually weighted line so that cancels out the extra cost," McNeill says.
Weighting lines to make them sink more quickly and take baits beyond the reach of seabirds is a bycatch mitigation measure adopted in the New Zealand ling longline code of practice.
Until the development of integrated weighted lines, the only way to do this was by clipping five-to-six kilogram weights onto the backbone every 30 -- 50 metres. However, external weights pose issues for skippers, including carrying the extra tonnage, inefficiencies in the time taken to attach and remove the weights, and risks to crew if heavy weights come back over the side too fast during the haul.
In 2002, New Zealand Longline, a joint venture Sealord and Amaltal won an $11,000 grant to trial an integrated weighted autoline.
The work was a collaborative experiment, with additional funding from the Australian Antarctic Division, Sealord, NZ Longline Ltd and Gourock. Fishing gear manufacturer, Fiskevegn produced the lead core autoline. Work on testing and improving the integrated weighted line is ongoing, McNeill says. Both officially, and by skippers and crews who have begun to use the gear.
Official New Zealand trials have been carried out on the Avro Chieftain and Janas, two New Zealand Longline vessels. Their experiences have lead to some improvements to fishing practices to make the integrated weighted line even more effective. "While the integrated weighted line works well through the current autoline set up, on the Avro Chieftain we have installed a line setter to pull the line through the baiting machine so it is slack as it enters the water. When used with an integrated weighted line, this technique takes the line to 10-metres very quickly."
Scientific trials into seabird catch rates and target fish catch rates have also been done within the areas covered by the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) and the Australian toothfish fishery.
Normally, manual line weighting is required in these areas, but exemptions were given to trial the new device.
The outcome was more fish being caught. Good news travels fast, and integrated weighted line is now being trialled in the French toothfish fishery around Kerguelen Islands, and Alaska.
However, McNeill says it is unlikely that this gear can be a global golden bullet. While it can be used on most New Zealand autoline vessels, and has been found to be very effective, differences in fisheries around the world make it unlikely integrated weighted line can be the global answer to seabird mitigation.
There will always be a need, he says, for fishermen to identify the bird species in the area and how they are feeding, then try and reduce incidental bycatch using the range of mitigation devices and methods that are compatible with their fishing practice.
New Zealand Longline is working with Dr Graham Robertson of the Australian Antarctic Division comparing target species catch rates with un-weighted standard line and integrated weighted line. "Graham is hoping to prove that integrated weighted lines will catch as much, if not more, of the target catch.
The intention is that if this proves to be true, even the illegal longline vessels will buy this gear, and then we'll have the spin-off of reduced seabird deaths within that fleet," McNeill says.
"We also want to develop similar gear for use in the Spanish-method demersal longline fisheries around the world, as this is the main longlining method used for catching toothfish and other bottom dwelling fish species."
