Scientists shine new light on salmon farming

THE numbers of sea lice on Scotland’s salmon farms are not increasing, farmers have better control of parasites today than in the past, and the risk of disease transfer from farmed to wild fish is low.

A very different picture of the state of Scotland’s salmon industry emerged yesterday when leading fish health experts appeared before Holyrood’s new inquiry into the sector.

Professors Herve Migaud and James Bron, both of Stirling’s Institute of Aquaculture, were the first to give evidence – along with Professor Paul Tett, reader in Coastal Ecosystems, from the Scottish Association for Marine Science (SAMS), and economist Steve Westbrook – at yesterday’s opening session of the Rural Economy and Connectivity (REC) committee’s investigation into salmon farming.

Asked by Richard Lyle, SNP MSP for Uddingston and Bellshill, about recent high mortality rates at salmon farms, Bron, the IoA’s Professor of Aquaculture, said there was a diverse range of health challenges at the moment.

‘The impression is that we’re getting a lot more sea lice, but if you look at actual figures, numbers of sea lice are not increasing. Many farms may have no problems with sea lice, some sites have serious problems; mostly, sea lice are under control in Scotland…the average has remained relatively static.

‘To manage to stay on top of that is quite a feat. The industry has not sat back,’ he said, noting that there had been more innovation in treatments in the last five years than there had been across a much longer period.

But it’s more difficult to treat sea lice because of gill health problems, and the industry has been in a transition period, moving from veterinary medicines to relying on a different approach, involving different tools.

‘We’ve had to learn how to deal with these problems but the industry has learnt how to cope with those.’

Putting farmed salmon mortalities (around 20 per cent last year) into context, Migaud, Professor of Aquatic Breeding and Physiology, said salmon mortality in the wild is about 90 per cent.

‘In some cases it’s 70 per cent, but it’s up to 99 per cent most of time. That doesn’t justify what’s in farmed but that’s the biology.’

In most important finfish species, mortality rates are high. The lowest mortality is in sea bass and bream, which has up to 45 per cent survival, but cod survival is lower than 10 per cent.

As for the causes of wild salmon mortality, Bron said unless dead fish wash up on beaches it is hard to tell how they died. The ocean is a ‘black box’ and very difficult to access.

‘Even without fish farming, wild fish can have 70 per cent infected with sea lice, without impacting their health. So working out the effect on wild fish is very hard to do.

‘We’re farming something not far from a wild fish, so they tend to have the same diseases. The potential for introducing diseases to the wild population is therefore low.’

Farmed salmon are not fed ‘unprocessed trash fish, introducing pathogens’, and there are very good controls on the movement of salmon.

The launch of the REC committee’s inquiry follows the conclusion of an investigation into salmon farming’s environmental impact, conducted last month by the Environment, Climate Change and Land Reform (ECCLR) committee.

Earlier this week it released its findings, criticising the industry’s environmental performance, and warning that Scotland’s marine ecosystem faces ‘irrecoverable damage’ from salmon farming if concerns are not addressed.

The ECCLR probe was informed by a report produced by SAMS, but Tett, one of the authors of the report, conceded to the REC inquiry yesterday that ‘our report may not be completely up to date’ because it was based on a review of existing literature.

Also, much of the information in the review was derived from Norwegian data but, as Tett, Migaud and Bron all pointed out, the two countries have some significant differences.

Norway’s fjords, for instance, are deeper than Scotland’s lochs, weather is colder –especially in the north, and the scale of farming is much bigger.

Migaud said that Norway has an extended coastline and there are a lot of local differences between the north and south – ‘we can’t apply what happens there directly to Scotland’.

The number of escapees entering rivers is also much higher in Norway than it is in Scotland, said Bron.

Fulton Macgregor, SNP MSP for Coatbridge and Chryston, was concerned about resistance to antibiotics and asked the panel how widespread their use was in Scotland.

Bron said ‘tiny… we use almost none’, and far less than other salmon farming countries, such as Chile, because of the development of very effective vaccines.

The academics were also able to reassure MSPs on the subject of stocking densities, when Richard Lyle suggested less density would be better for fish mortality.

Densities in the early days of salmon farming had been higher, said Bron, but ‘work we did established cut-off points for where health and welfare might suffer, so farmers all use lower density, and I think it’s about right.’

Migaud said current densities were 15kg per cubic metre for salmon, but explained to the committee that it was a challenge to get the fish to use their space better – ‘they are not fish that like to swim in isolation, they tend to congregate together’.

Conservative MSP for North East Scotland Peter Chapman asked how effective cleaner fish were, while committee convenor Edward Mountain (Conservative, Highlands and Islands) wondered if there was a market for wrasse and lumpsuckers, once farmers had finished with them.

Migaud agreed that was a very important consideration and that the industry was already looking into it. There was a potential export market for wrasse in Asia, while chefs around the world were trying to be innovative in finding uses for lumpfish – ‘but we’re still not there’.

However, greater progress was being made in farming cleaner fish. There were challenges regarding the robustness of the fish before deployment, but ‘we’re prototyping vaccines at present’, said Migaud.

The majority of cleaner fish are now farmed and in a couple of years the industry would be fully supplied by farmed lumpfish and wrasse.

This was one example of good collaboration between the industry and academia, but there were plenty more, with ‘fantastic innovations’, many appearing in the last five years and so still bedding down, said Migaud.

These included the use of recirculation hatcheries to reduce the time fish spent in open cages, optical delousing, functional feeds to boost mucus production and reduce sea lice attachment, and wellboats with reverse osmosis, capable of producing freshwater.

If there were knowledge gaps in the Scottish industry they were being addressed.

The convenor asked all panel members if they believed the target to double growth by 2030 could be achieved without detriment to the environment.

Tett said yes, ‘but there will need to be radical changes in the way farming is managed and regulated’, while Migaud said ‘it has to be done sustainably to meet this growth’, and Bron noted that problems needed to be solved, but the industry was working hard.

Steve Westbrook, author of a report on the value of aquaculture to Scotland, thought 50 per cent growth was much more likely than 100 per cent, even if everything was favourable, and getting to 300,000 tonnes was more likely than 400,000 tonnes.

But if the technology could generate more farms in offshore sites to get larger volumes, and there was less need to operate inshore sites, ‘a lot of the issues discussed will fade away’.

The next session of the REC committee will be on Wednesday, March 14, when MSPs will hear from Scottish Environment LINK, Salmon & Trout Conservation (the angling lobbyist which prompted the inquiry), Fisheries Management Scotland, and the Lochaber District Salmon Fishery Board.

Picture: Professor James Bron and Professor Herve Migaud at the inquiry yesterday

 

 

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