Fish health chief says sea lice control has improved

man sat in committee room

Action to control sea lice numbers on Scottish fish farms has been successful, partly driven by the new requirement to report lice numbers on a weekly basis.

That is the verdict of Charles Allan, group leader of the Scottish Government’s Fish Health Inspectorate (FHI), in the evidence he gave to the Scottish Parliament’s Rural Affairs and Islands (RAI) Committee this morning.

He said: “I think the sea lice situation on farms in Scotland has changed significantly… we have seen sea lice numbers come down on farm. In the last year we have offered no enforcement notices.”

He was giving evidence in the second session of the RAI Committee, which is reviewing the Scottish salmon industry, following a previous inquiry which reported in 2018.

Allan said the level of six sea lice per fish, which was previously the statutory level for mandatory intervention, had been exceeded only once in the last reporting year.

Asked whether sea lice numbers had gone down, he replied: “Yes – that’s borne out by the data… and almost never do we see the clinical results of infection.”

Arguing that the management of sea lice in farmed fish populations in Scotland had improved, he stressed that the role of the FHI is not only to enforce penalties but to encourage continuous improvement.

He said: “If I have to apply the stick, I would see myself, as a regulator, having failed.”

Challenged by the committee over instances where farmers had recorded “no count” of sea lice, he explained that there were a number of commonsense reasons not to count sea lice, such as weather or veterinary advice, and also that fish about to be harvested are not counted because a period of time needs to elapse for the fish to be clear  anaesthetic – which is needed to examine the fish for sea lice – before it is offered for sale.

The latter exemption had been claimed in a few contentious cases, Allan said, and he added: “There are a few sites where significant periods of time were covered by ‘no counts’. We have made representations and have been assured it would not be repeated.”

Allan said the use of new approaches by farmers – such as thermolicer, hydrolicer and freshwater treatments – had improved the situation, together with good husbandry such as fallowing sites to reduce sea lice populations.

He denied that sea lice treatments are inherently damaging, arguing: “A well commissioned sea lice treatment on clinically healthy animals should have no detrimental effect on them.”

He warned, however, that where fish health was already compromised, for example by gill health issues, some fish may perish after treatment.

Ariane Burgess MSP

Ariane Burgess, Green MSP for Highlands and Islands, asked whether the statistics showed that increasing numbers of farmed salmon were still dying, and whether the industry was still expanding despite this.

Allan said: “The rate of mortality in Scottish aquaculture is relatively stable, but the causes of mortality vary in time and space.”

He added that while the total  consented biomass had increased, the biomass actually put to sea, and the amount harvested, had not grown at the same rate.

Edward Mountain, Conservative MSP, Highlands and Islands, asked why the figures for 2022 showed that 36,000 tonnes of fish had been lost prior to harvest, a bigger number than in previous years even though production had not increased.

Allan explained that rate of mortality, as a proportion of fish put to sea failing to reach harvest, has remained “remarkably constant” at around 75%, but the age at which fish are dying has increased.

As he put it: “Twenty-five per cent of a small biomass is a relatively small number. If you grow those fish for a year and then they die, the same number of fish have died but the tonnage increases. Bigger fish are dying.”

The MSPs also put questions on the impact of climate change, health and welfare for cleaner fish and the relationship between warmer winters and fish mortality.

The next session of the inquiry, covering licensing and consenting issues, is due to take place on Tuesday 18 June.

Edward Mountain MSP


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