Scottish salmon farms failing to control lice, says report

These parasites are of concern not just due to their impact on farmed fish welfare but because there is a risk they may then infect wild salmon, which are in serious decline.

Since March 2021, active marine net salmonid farms have been legally required to report weekly average female sea lice levels. Breaching the Limits analysed such industry-reported sea lice data, Fish Health Inspectorate records, and reported chemicals usage.

It revealed that last year the Scottish industry breached its own guidelines, or failed to supply a lice count, for 40% of its counts.

It also pointed out the lack of industry compliance with its own code of good practice sea lice threshold guidance, “despite these being five times more lenient than thresholds considered best practice in neighbouring Norway”.

Marine Scotland has a maximum level of six lice per fish before enforcement is triggered, and two per fish before surveillance is increased, but Norway has thresholds ranging between 0.1-0.2 and 0.5 in the most sensitive period for wild salmon impact.

Rachel Mulrenan, Scotland Director for WildFish, said: “This analysis of industry sea lice data from last year is yet another demonstration of why the Scottish Government needs to take urgent and strong action to tackle sea lice infestations on salmon and trout farms in our coastal waters.”

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Particularly concerning, the report said, were lice levels during what is described as “the sensitive period”, the period of young salmon migration, when wild salmon are most vulnerable to sea lice due to their small size, which were reported at levels that exceeded the industry limit guidance on 1 in 4 occasions.

More than two-thirds (130 of the 192)  marine open-net salmon farms breached CoGP sea lice limits on at least one occasion.

The Norwegian company Mowi, the report said, recorded sea “lice levels as high as 8.2 lice per fish on one of its farms; 16 times the industry limit, and 40-80 times higher than what would be permitted in the company’s home country of Norway”.

A Mowi spokesperson said: “Mowi takes its obligation to effectively manage sea lice levels on its salmon farms very seriously. Our teams of fish health experts and veterinarians regularly monitor sea lice on our salmon and will quickly intervene to reduce levels if required. For many years now, our sea lice monitoring data and successful management results are posted monthly online for the public to see.”

Wildfish’s figure of 2 billion fish from one farm is calculated based on a single farm which reported an average adult sea lice per fish of 8.2 in week 12 of 2022, and held, according to the report’s calculation, 602,692 salmon – and used egg production and hatching success data.

Moreover, it showed that there was a data gap resulting from a high instance of “no counts” in which numbers were not reported.

Graph from the Wildfish Breaching the Limits report

Loch Duart was the worst-performing producer overall in relation to sea lice numbers. The report said: "Over a third of sea lice counts provided by the company in 2022 were above the industry thresholds; and one of its farms breached Marine Scotland’s 2.0 sea lice limit a total of 19 times – far more than any other producer."

A spokesperson for Loch Duart said: “Wildfish’s latest attempt to discredit our business by cherry-picking data misleads. At Loch Duart, we are committed to doing things differently when faced with the environmental and fish health challenges created by rising water temperatures. We choose to deploy natural treatments over chemical or mechanical ones, such as our pioneering use of cleaner fish and freshwater treatments, simply because we believe it’s the right thing to do for our fish and the environment.”

“Farming this way means that there are times of the year when sea lice levels will naturally elevate, but by allowing our cleaner fish programme time to work it has been repeatedly shown they will bring sea lice down to low levels. Loch Duart is the only salmon farm that invites a local fisheries trust on-site to independently audit its fish health data, going over and above the industry standard on sea lice reporting.”

Loch Duart also reported that the average weekly sea lice levels across all their farms in 2022 was 0.85.

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Dr Matt Palmer, Farmed Salmon Campaign Manager at WildFish, said: “These parasites cause significant health, animal welfare and mortality issues both on the farms and in our wild salmon and sea trout. Poorly controlled, not only do they expose the farmed fish to distress, pain, injury and disease, but they multiply in their billions. Simply swimming past these farms could then prove fatal to our wild fish.”

Ms Mulrenan added: “The Scottish salmon farming industry lauds its Code of Good Practice as ‘world class’; a supposed indication that Scottish salmon and trout farms have their sea lice numbers under control. However, our analysis shows that this is misleading on a number of levels – not only is the industry failing to comply with the Code for up for 40% of the time, with no repercussions; the Code itself is far too lenient as to be effective, and the counts are unverified."

Graph from the Breaching the Limits report showing increase in use of the lice treatment emamectin benzoate between 2021 and 2022

Responding to the report, Tavish Scott, chief executive of Salmon Scotland, said: “Sea lice are naturally occurring and affect both wild and farmed fish populations. Scotland’s salmon farms consistently demonstrate low average levels of lice, thanks to farmers, vets and fish health specialists, with fish health and welfare our farmers’ top priority.”

The Breaching the Limits report recommended that the Scottish Government should close open-net salmon and trout farms and “encourage alternative aquaculture practices that are less environmentally damaging” and that Scottish Government should “immediately introduce absolute limits on sea lice numbers on fish farms, in line with the best available science and the precautionary principle”.

The Scottish Government, Wildfish said, should not rely on industry self-regulation - rather SEPA should “close reporting loopholes and independently verify industry-supplied sea lice data”.

A Scottish Government spokesperson responded: “The Scottish Government takes the issue of our declining salmon stocks very seriously and is committed to working with our partners, both domestic and international, to safeguard this iconic species.

“We value the role of aquaculture in producing world-renowned healthy and quality seafood, through sustainable food production, however we recognise that its delivery and development must be sustainable and with appropriate regulatory frameworks whilst maintaining high environmental standards.

“We remain committed to ensuring the regulation of the interactions of sea lice and SEPA is preparing for a further phase of consultation on a sea lice risk assessment framework this spring. We are also exploring how to strengthen the escapes regulatory regime, including the introduction of penalties where fish farm escapes occur.”