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