Integrated weighted line

Integrated weighted line

The world's Antarctic and subantarctic waters contain valuable longline fisheries for toothfish - Dissostichus eleginoides and D. mawsoni.

In waters south of 60° S Latitude, fishing is controlled through regulations set by the Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR). This organisation was set up under the Antarctic Treaty to conserve marine life and ensure any harvesting is carried out in a rational way, supported by science.

In 2000, CCAMLR set new line-weighting standards that vessels using automated baiting/setting systems had to meet before they could fish in Antarctic waters.

Under these regulations, several New Zealand autoline vessels were developing a fishery in the Ross Sea. These vessels spent part of the year fishing for toothfish in the Ross Sea and the remainder of their time fishing for ling in New Zealand waters.

The line-weighting regime meant these vessels had to attach heavy weights one by one as they set the line, and then take them off again as they hauled the line. They also had to move weights around the vessel - from the hauling room to the setting room.

Malcolm McNeill was managing some of these autoline vessels for the company New Zealand Longline Ltd. He says all this work with weights meant a vessel could only put about two-thirds the number of the hooks in the water. This was acceptable then for his vessels in the Ross Sea, but it was less economic when they fished for ling in New Zealand waters. However, Malcolm says that in New Zealand, these vessels were coming under increasing pressure to use line weights, because of seabird bycatch in the ling fishery.

Malcolm knew fishing and gear and had the support of his company - from the chief executive down. He was determined to find a solution to the seabird issue on his vessels.

On the other side of the world, Australian Antarctic Division seabird scientist Graham Robertson was working with Washington Sea Grant scientist Ed Melvin on ways to reduce bird deaths on longline fisheries in Alaska's Bering Sea.

They knew that line-weighting worked, but that it had problems. While the attached weights would sink surrounding hooks quickly, the line and hooks between the weights would 'balloon' upwards and so remain close to the surface for longer. This meant some seabirds would still be caught.

In 2000, Graham and Ed thought that if you could integrate the weight into the line, then it might eliminate the 'ballooning' effect that weights caused. New Zealand Ministry of Fisheries scientist Neville Smith also had similar ideas.

Graham and Ed played around with wrapping lead around lengths of line and then dropping this behind the boat to see how quickly it would sink. They used time/depth recorders to check this. They found that if you integrated lead into the line, you got great sink rates and a linear sinking profile.

Malcolm heard Graham and Ed talk about their trials with integrating lead in the line at the 2001 International Fishers' Forum in Auckland, New Zealand. Inspired by this as a possible solution, he spoke with fishing gear suppliers about the issue facing his vessels. Eventually, he sparked the interest of a young sales representative from Fiskevegn.

Fiskevegn's line-makers went to work figuring out how to put lead into a line without compromising the line's strength and durability.

In 2002, New Zealand Longline Ltd won a NZ$11,000 grant from funds raised on vessels affiliated with the International Association of Antarctic Tour Operators (IAATO) to trial Integrated Weighted (IW) with various amounts of weight. The work was a collaborative experiment, with additional funding from the Australian Antarctic Division, Sealord, NZ Longline Ltd and fishing gear distributor Gourock. Fishing gear manufacturer Fiskevegn supplied four sample 'magazines', each containing a differently weighted line - 25, 50, 75 and 100 grams/metre (as had been recommended by Graham).

Additional trials were also done on two vessels near Alaska's Aleutian Islands in 2002.

These initial trials showed the 75 and 100-gram lines were impractical, but that the 50-gram line performed well - coiling consistently on the magazines and passing through the autoline system with fewer difficulties that traditional gear.

Graham recommended the 50 gram/metre IW line be fully tested on the NZ Longline vessel Janaslater in 2002. These trials were arranged by Neville Smith through the New Zealand Ministry of Fisheries. Neville had been researching line-weighting regimes in New Zealand autoline fisheries and had taken an interest in the IW line's development.

Neville arranged the agreement of New Zealand's Minister of Fisheries for scientific trials to test the IW line. This was necessary, because to prove how effective the line was, it needed to be tested against an unweighted line. This meant comparing how many birds were killed using IW line with how many were killed using conventional line.

The experiments were carried out in the Solander region of New Zealand's subantarctic during October/November of 2002 and 2003. This region at this time of year is renowned for having large numbers of hungry white-chinned petrels - a diving species that are particularly hard to mitigate against. Graham, Malcolm and Neville all knew that if IW line worked here, it would work anywhere.

Around 1.1 million hooks were set during these experiments. They showed a 94% to 99% reduction in catch of white-chinned petrels and 61% to 100% reduction in catch of sooty shearwaters when using IW line compared to unweighted line. Catch rates of target and non-target species were reported to be similar for both lines.

Line sink rates of IW line are similar to the sink rate required by line weighting in CCAMLR waters. However, IW line has some seabird mitigation and fishing advantages over using a conventional line with line weights. These are: the line and hooks do not 'balloon' between weights; the line is a little stiffer than conventional line, making it easier to handle when setting and stowing; IW line is safer than handling heavy weights in rough seas; and IW line catches more fish - because the crew don't need to spend time taking weights on and off. Also, because IW line sinks more quickly that conventional line, baits reach the bottom sooner (the longer baits are in the water, the more they lose their smell and attractiveness to fish).

For all these reasons, IW line has become the line of choice for autoline vessels fishing for toothfish in CCAMLR waters and for ling in New Zealand waters. In 2005, CCAMLR fisheries involved 15 such vessels, all of which used IW line.

Line weighting is not legislated in other autoline fisheries around the world, so line weighting has not been adopted elsewhere to the same extent.

While the line is around 10% to 15% more expensive than conventional line, most fishermen who work with IW line "really like it" says US mitigation researcher Ed Melvin. He reports that in 2009, 4 out of the 36 autoline vessels fishing Alaskan waters used the IW line.

Fiskevegn were the first company to produce the IW line for autoliners, but its popularity means they are now not the only company to manufacture this product.

In terms of governments legislating for its use, IW line has a major advantage over line weights. Because if you check a vessel in port and find it is carrying IW line, you know that it will be fishing with this once it leaves port. With line weights, a vessel can be carrying them, but unless you have an observer on board, you will not know whether they are using them or not.

Links and references

Leigh S. Bull, (2007) A review of methodologies for mitigating incidental catch of seabirds in New Zealand fisheries Department of Conservation Research & Development series 263: pp 26-29.

Kimberly S. Dietrich, K.; Melvin, E.; Conquest, L. (2008) Integrated weight longlines with paired streamer lines - Best practice to prevent seabird bycatch in demersal longline fisheriesBiological Conservation 141 issue 7 (July 2008): pp 1793-1805.


Robertson, G.; McNeill, M.; Smith, N.; Wienecke, B.; Candy, S.; Olivier, F. (2006) Fast sinking (integrated weight) longlines reduce mortality of white-chinned petrels (Procellaria aequinoctialis) and sooty shearwaters (Puffinus griseus) in demersal longline fisheries.Biological Conservation 132: pp 458-471.

Seafood mitigation from a man in the know. Seafood New Zealand magazine March 2003. vol 11, no. 2: pp 54-55.

Integrated and innovative Seafood New Zealand magazine August 2004. vol 12, no. 7: pp 40-41.

Willing French fishers are finding a way Seafood New Zealand magazine October 2004. vol 12, no. 9: pp 52-53.

Agnew, D.J.; Black, A.D.; Croxall, J.P.; Parkes, G.B. (2000) Experimental evaluation of the effectiveness of weighting regimes in reducing seabird by-catch in the longline toothfish fishery around South Georgia. CCAMLR Science 7 (2000): pp 119-131. (