Aquaculture for all

Why Scottish salmon farmers love skirts

Atlantic Salmon Sea lice +3 more

The deployment of skirts to keep sea lice out of salmon pens is proving very effective for Scottish Sea Farms, with the salmon in the pens involved outperforming all previous year classes following the introduction of the fabric barriers.

The new shields are the latest in a series of proactive, preventative measures by the company to enhance the health and welfare of the salmon under its care. Specially engineered to suit Scottish marine conditions, each consists of a permeable fabric that lets water and oxygen move freely into fish pens whilst keeping parasites out. This fabric fully encases the pen to a depth of 6m, providing a barrier against sea lice, which are most commonly found in the first few metres below the water’s surface.

The new shields were first introduced at the company’s farm in Ronas Voe on Shetland in May 2017. In the nine months since, sea lice levels have successfully remained below the Marine Scotland Code of Good Practice threshold, and the salmon are showing strong growth and biological performance.

A graphic illustrating how the sea lice shields work

Such has been the effectiveness of the shields that Scottish Sea Farms has now invested over £800,000 with two Scottish suppliers – William Milne Tarpaulins in Aberdeen and W&J Knox in Ayrshire – in order to roll-out similar protection to 11 of its other farms.

The company is also working with neighbouring salmon growers to synchronise use of the shields, as part of a farm management agreement for those same areas.

Jim Gallagher, managing director of Scottish Sea Farms, says: “We strive, wherever possible, to replicate the natural conditions that salmon are known to thrive in. As any farmer will understand, however, this comes with its own risks, as the marine environment presents new challenges all the time. We are continually exploring and investing in new ways of dealing with these challenges, and it’s hugely encouraging to see positive early results such as these at our trial project in Shetland.”

This latest advance is part of a wider £11.8 million investment in 2017 by the company to enhance the health and welfare of its salmon – over 85 percent of which is being spent on non-medicinal approaches.

In terms of controlling the sea lice challenge specifically, key areas of investment include:

  • More than doubling the use of cleanerfish, in the last year – 76 percent of which are now from farmed origin, keeping the company on track to use farmed-only stocks by 2020.
  • Developing a new net cleaning pressure pump to keep pens free from marine build-up, simultaneously enhancing fish health and welfare and increasing the effectiveness of cleanerfish.
  • Ongoing investment to increase understanding of cleanerfish, with the insights gleaned being shared with the wider industry.
  • Co-funding new Thermolicer technology that bathes salmon in such a way as to dislodge and catch sea lice, with up to 95% effectiveness.

In turn, the need to administer medicines has significantly reduced, with six of the company’s farms requiring no medicinal sea lice interventions at all during 2017.

Other investments

With the UN reporting that the last three years were the hottest ever on record, and Scotland’s rising sea temperatures resulting in new planktonic organisms that are potentially harmful to the health of fish gills, the company has also invested approximately £200,000 in state-of-the-art environmental data monitoring equipment, as well as over £260,000 on new underwater camera systems.

Ralph Bickerdike, head of fish health at Scottish Sea Farms, says: “Even a seemingly slight increase in sea water temperatures of 0.5 degrees can have an impact on the marine environment. This new data monitoring equipment is enabling real-time analysis of key markers such as salinity and oxygen concentration, helping us to make informed decisions to maintain high standards of welfare for the fish under our care.

“Complementing this, the new underwater cameras enable us to observe the fish within the pens and respond swiftly should there be any changes in their natural behaviour.”

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