Tube Net

Fish Farmer - - Contents -

THE Nor­we­gian made Tube Net, also some­times called a ‘snorkel’, has had con­sid­er­able suc­cess tar­get­ing sea lice and is now un­der­go­ing tri­als to tackle AGD as well. Since 2014, the sys­tem – for farm­ing salmon be­low the wa­ter sur­face, where lice lev­els are much lower – has been de­ployed by Bremnes Seashore at its sites in Ro­ga­land in south­ern Nor­way.

Apart from achiev­ing up to 90 per cent re­duc­tion in lice num­bers com­pared to or­di­nary nets, the Tube Net has also helped in the fresh­wa­ter treat­ment of gill dis­ease.

Now, said Eger­sund Net, the com­pany be­hind the Tube Net, a full-scale trial is un­der­way at Bremnes to see just how ef­fec­tive the in­no­va­tion is.

Tom As­b­jorn Hatleskog, ex­port sales man­ager of Eger­sund, said Bremnes has ex­tended Tube Nets to more sites, and im­prove­ments have been made to fa­cil­i­tate fresh­wa­ter treat­ment.

‘A year ago they got AGD and de­cided to try us­ing the tube to ad­dress this prob­lem too,’ said Hatleskog.

there to clean their gills and soon the amoeba was gone.

more solid PVC strip to avoid the leak out of the fresh­wa­ter in­side the tube into the salt­wa­ter.’

Bremnes, in con­junc­tion with the Nor­we­gian In­sti­tute of Marine Re­search – which was in­stru­men­tal in de­vel­op­ing the Tube Net - is now try­ing to op­ti­mise the sys­tem.

At one big site, the com­pany has in­stalled Tube Nets on half the pens and will be test­ing these against tra­di­tional nets for a re­duc­tion in lice and also gill is­sues.

Net com­pared to tra­di­tional meth­ods us­ing tar­pau­lin.

The tube has gen­er­ated a lot of in­ter­est, said Hatleskog, and is com­mer­cially avail­able, but Eger­sund is learn­ing with Bremnes about how to get the best out of it.

‘Han­dling ev­ery­thing is com­pletely dif­fer­ent and we needed to make sure that we did things cor­rectly with Bremnes and learnt in the process - we keep a con­stant fol­low up.

‘The chal­lenge is that this is a new way of farm­ing so you need to look at things, like keep­ing the nets clean – that’s one of the main chal­lenges.’

Bremnes uses cop­per as an anti-foulant which, in Ha­tel­skog’s view, is prefer­able to other meth­ods of keep­ing the nets clean, but this is con­tro­ver­sial be­cause to meet the stan­dards of Nor­way’s new green con­sents, farms are not al­lowed to clean cop­per anti-foul­ing nets at sea.

‘It’s the same with the ASC stan­dard… you have to change the net when the cop­per has done its job.’

But marine foul­ing is ‘very, very com­plex’, said Hatleskog, adding that Eger­sund, as a man­u­fac­turer, ‘wants to be per­ceived not just as a sup­plier but also as an ad­vi­sor’.

‘That is why, to­gether with some of the man­u­fac­tur­ers of anti-foul­ing, we col­lab­o­rate very closely and con­stantly do tri­als all year, all along the coast in Nor­way and also in the Mediterranean, to see what the op­ti­mum anti-foul­ing is this year. As seasons change you would also have new in­va­sive species.’

He said that the Nor­we­gian farm­ers who use anti-foul­ing tend to use the higher pre­mium prod­ucts, but clean­ing prac­tices vary from one farm to an­other.

‘What we’ve seen in other mar­kets and in Nor­way too is that you put anti-foul­ing prod­ucts to sea and even­tu­ally they start to foul, and then it’s up to the farmer to de­cide what to do.

‘The ten­dency has been to clean as quickly as pos­si­ble and they use pres­sure on the net of up to, say, 300 bars, which is a sub­stan­tial amount of pres­sure to keep on the net.This re­sults in the cop­per be­ing blown away and has no ef­fect

what­so­ever.And the cop­per waste ends up in the seabed.

what’s on the nets and not the lice,’ said Hatleskog.

He de­scribes the strat­egy of one of the small, fam­ily owned com­pa­nies that man­ages to keep the net clean and also helps in the re­duc­tion of lice.

‘What he has done for many years is use anti-foul­ing on the nets and af­ter one week and on com­pletely clean nets, they would start to wash, but us­ing only 100 bars. That re­moves an in­vis­i­ble layer, all these spores. And by us­ing a small amount of pres­sure, you man­age to cre­ate a stir in the cop­per, al­low­ing the cop­per to re­act and to start work­ing. ‘If you washed your car with 300 bars you’d blow the paint away` in gen­eral.

‘It is the per­cep­tion of cop­per that needs to be changed. If it was up to and just change the net – when the cop­per has lost its ef­fect, af­ter seven or eight months, and, what we see in most cases, bet­ter growth and health in gen­eral.

‘That is what some of these small farm­ers do and they are the ones that get the best re­sults the best growth and fewer gill is­sues.And also they save cost, they say, long term with such a strat­egy.

‘No­body has ever done a proper trial com­par­ing a site with no cop­per but high pres­sur­ing the net, to one with cop­per and do­ing a net change in­stead of wash­ing.

‘To get a proper com­par­i­son you would need bench­mark­ing for an en­tire cy­cle, com­par­ing ev­ery­thing - the cost of the net, the cost of the anti-foul­ing, the cost of wash­ing the net, the la lack of treat­ment be­cause you don’t have any gill is­sues, re­duc­tion of lice.

‘If some­body had done such a trial it would be a rev­e­la­tion.’

Any­one can see the tri­als at Bremnes, which is happy to share its re­sults – ‘the down­sides and the up­sides’ – with other farm­ers who want to see how the Tube Net per­forms in prac­tice.

There has been in­ter­na­tional in­ter­est in the tube but dif­fer­ent farm­ing con­di­tions might need a cus­tom made model of the Tube Net, for shal­lower wa­ter..

Left and be­low: Images from the power point Dr Frode Oppedal, of Re­search, at the sea lice con­fer­ence in West­port

Right: Tube Net at the sur­face

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