Sea Lice Top tarps

Shields prove effective preventative tool against parasites

THE kilt is an iconic symbol of Scottish heritage, with its distinct tartan design and the mythology about how it is worn illuminating many a fireside discussion with a few wee drams. However, for Scottish fish farmers it is an altogether different kind of skirt that has been their main focus of attention over the past few years. Tarpaulin technology in the form of the sea lice skirt has advanced to a stage where the fabric can now provide a very effective weapon in the protection of fish from sea lice.

For example, when Scottish Sea Farms (SSF) introduced the skirts at the company’s farm at Slocka, Ronas Voe, on Shetland in May 2017 they saw their crops outperform all of the previous years’ results and so rolled out the treatment to 11 other sites.

Specially engineered to suit Scottish marine conditions, each skirt consists of a permeable fabric that lets water and oxygen move freely into the fish pens, while parasites are kept at bay.

The fabric typically fully encases the pens to a depth of 6m, providing a barrier against sea lice, which are usually found in the first few metres below the water’s surface.

The SSF lice skirts were provided by two Scottish suppliers, William Milne Tarpaulins from Aberdeen and W & J Knox from Ayrshire.

William Milne designs, manufactures and supplies all its sea lice skirts directly from its Aberdeen factory.

Meanwhile, W & J Knox works in conjunction with partners Garware Wall Ropes, headquartered in Pune in India. Garware’s robust and porous woven X12 material has a very high water flow, with good dissolved oxygen and water exchange, said the company.

Chairman and managing director Vayu Garware told Fish Farmer last year that one litre of water goes through the X12 fabric in six seconds, compared to around seven and a half minutes in other lice skirts.

In trials in Chile with square cages, two head cages were treated with X12 lice skirts and the rest were treated only using pharmaceuticals. After a full, 13-month cycle, there was a 55 to 60 per cent reduction in sea lice counts in the cages with the X12 skirts.

‘Additionally, the growth rate was better and they needed half the bath treatments,’ said Vayu Garware.

As part of continued innovation across the whole of its Indian operation, the company is also currently working on algae resistant, anti-microbial and UV resistant tarps with additional properties to be added.

Other significant players in the lice skirt market include Inverness based Tom Morrow, which produces a high quality and long lasting screen using 100 per cent non-degradable materials.

Tom Morrow screens are protecting salmon across the globe and the company offers fully enclosed or wrap around screens with or without floatation.

Marcus Sanctuary from the company said: ‘We always say, as a general rule, that our lice skirts should prevent 70 per cent of sea lice occurrence. The lice can be found in the top five metres of the net, and our shields cover six metres.

‘The best way to think of them is like a curtain blind. They pull up and down as required. All of

ours are specially weaved here in Scotland, and although pretty much all suppliers use the same sort of materials, we place our emphasis on strength and durability.

‘We do offer cheaper options, but I would say that when it comes to really heavy duty installations then that would be our speciality. But there is no doubt that this is a great prevention method.’

Norwegian company FiiZK (which includes Botngaard) has developed a new version of its lice skirt which it claims has revolutionised the way in which lice skirts are made.

The Trondheim based company also offers delousing tarps, which are used for freshwater bath treatments.

Fiizk’s aquaculture tarpaulins sales manager Jan Borge Harsvik said: ‘The big advantage with the delousing tarps is that you don’t need to handle the fish. This greatly reduces the mortality risk.

‘When it come to the sea lice skirts, the big advantage that Fiizk has is our huge production facility, which means we can offer a better cost benefit value.

‘We have a modern production line, good logistics and excellent R&D and this all adds up to a really short turnaround time compared to some other suppliers.’

Also making a name for itself in the sea lice skirts market is Cunningham’s of Ireland, with offices north and south of the Irish (now EU) border.

The company custom makes lice skirts for fish farms in any shape or size required, and says its bespoke skirts are extremely durable and suited to withstanding harsh marine environments.

“The best way to think of them is like a curtain blind, they pull up and down as required”