A Scottish salmon farm visit. Haunted by mortalities and jellyfish

But they also related stories of struggles. “It’s a very personal thing for the team to get the fish in at 200 grams and then get it to 5kg and to market,” said one of the farm team.

“And it’s heartbreaking for the guys when the fish are hit by a problem.”

Another farmer shook his head as he recalled the micro-jellyfish blooms that blighted some farms over the past autumn.

The farm hand said: “We’ve never seen them like they were the end of last year, which was catastrophic.”

The issue of micro-jellyfish is a repeated refrain, though this farm, Fishnish, was not impacted by them last year.

Anne Anderson, the director of sustainability for Scottish Sea Farms, said: “This farm was okay, but what might come in next year? What will the seas bring us? That’s the thing. I’m constantly thinking what will the seas bring, where will it occur? And that’s why that ocean monitoring, to give us an early warning, is so important.”

The big news around the time of my visit was the devastating wave of mortalities that had hit Scottish salmon farming in the past year. Between January and November 2022, according to Fish Health Inspectorate (FHI) data, nearly 15 million deaths were reported by farms in Scotland, double that of 2021.

Meanwhile, according to the Salmon Scotland website, the average mortality rate across the industry is 14.5 percent (compare with 4 percent in chicken farming, according to the British Poultry Council) though some salmon farms have rates far higher than that.

Part of this story is believed to be down to jellyfish. In November last year, Scottish Sea Farms reduced estimates for its 2022 harvest by 8000 tonnes, blaming the mortalities on micro-jellyfish and gill health issues.

They were not alone. Mowi, Bakkafrost and Cooke Aquaculture, said something similar. Mowi, for instance, slashed its harvest guidance by 17 percent, saying, “Our Scottish farming operations has experienced a troublesome year with regards to biology.”

READ MORE:The toxic salmon farm chemicals that are a risk to swimmers

Anne Anderson, copyright Scottish Sea Farms

Ms Anderson added: “Micro-jellyfish are the latest thing on top of a series of things. Small incremental differences in temperature, as we have with climate change, make a huge difference in the way that the tides and currents flow. They affect whether there are algal blooms and where they move to. We found micro-jellyfish at a level that has not been typically found in Scottish waters before.”

Less than 2mm in size, these hydrozoans are so small, said Anderson, that the filtration and monitoring required to catch them and see them “was the next level down from what we were using”. The damage they cause is believed to be through irritation to the salmon gills - and gill health is one of the biggest issues in salmon farming.

The salmon that swirled at Fishnish seemed to be thriving, but this was a farm that had only just been recently stocked. We were also visiting outside the time of year when problems like jellyfish and lice are at their worst.

Since my visit to the site, I’ve seen footage from last summer – not of this farm but of a companion Scottish Sea Farms site at Fishnish – filmed by an activist right up against the pen.

On just one of these fish, 40 lice could be counted between its nose and gill just on one side of its face.

Sea lice infestations are, of course, another of the challenges for Scottish salmon farms.

Ms Anderson added: “The range of tools to control sea lice has expanded over the years, ranging from freshwater baths through to medicated baths or one of the physical methods, such as the thermolicer and hydrolicer.”

Many of these methods, however, have their own welfare impact. One study, Factors Associated with Baseline Mortality in Norwegian Atlantic Salmon Farming, highlighted that there was a mortality increase seen within a month of “non-medicinal sea lice treatments, including thermal delousing”.

READ MORE: Papa Westray islanders call for referendum on giant fish farm

Ms Anderson was keen to counter criticisms of salmon farming. "Salmon farming," she said, "is a very small pinprick within a vast body of water, and for that we grow so much protein. In simple terms, for every hectare that we have, we provide 72,000 of GVA to Scotland.”

The seabed area occupied by salmon farms, in Scotland, she noted, is 1166 hectares, 0.07% of our inshore waters – this she compares to terrestrial farms, which occupy 80% of Scotland’s land. Like much farming, though, aquaculture’s impact reaches beyond the area it covers, whether that’s through the wash-off of its chemicals and effluent, or the impact in other places of growing its feed supply. Feed is key factor that has an impact on sustainability.

Over the years, Ms Anderson told me, the feed conversion ratio – of feed going in to salmon weight out – has gone down steadily.

She said: “The ratio is getting ever closer to that 1kg-to-1kg scenario. We’re at 1.15, occasionally under.”  We could compare that with, for example, beef which has a typical feed conversion ratio of between 6 and 10, but here we are comparing herbivore with carnivore, and we are looking at fish eating harvested wild fish - or at least some fish.

The pellets are made by Biomar, based in Grangemouth and only a relatively small level, 23%, is fish content, with the majority of raw materials being “non-marine ingredient” – plant matter such as pea proteins. Fish oil content is sourced from the Southern Seas, from a Peruvian anchovy fishery.

However, Ms Anderson said: “Salmon needs marine content. There is a balance to be struck to provide fish with the nutrition it needs such that it is healthy to overcome those challenges we are talking about.”

The shocking recent mortalities have spurred objections to the Scottish Government plan to expand salmon production. Earlier this month, a group of 10 MSPs signed an open letter, coordinated by Animal Equality UK and OneKind, calling for a moratorium on the expansion of salmon farming in Scotland. It said: “The sharp rise in on-farm mortalities has caused us to question the long-term sustainability of this industry”.

Faced by many challenges, the sector is innovating – and one of those experiments is the state-of-the-art hatchery Scottish Sea Farms took me to on my tour.

At Barcaldine, on the banks of Loch Creran, the company has built what’s called a land-based recirculating aquaculture system: a hatchery raising salmon from ova through to smolt.

There, in a huge building, salmon are kept in tanks, through which water from a reservoir is circulated.

The biosecurity is so tight the building feels like a high-security research facility, requiring changes of footwear, plastic shoe covers, white disposable suits, gloves, disinfectant pads and transition areas between multiple sealed-off parts.

Here, the fish begin their life incubating as ova, which progress, in this facility, through the salmon lifecycle all the way to smolt, when they are taken away to farms by boat.

READ MORE: Wild salmon 'canary' tells a tale of multiple damages

That battle to stave off disease and improve survival rates begins even before the eggs arrive. It starts with a new breeding programme in Dumfries and Galloway, based around the highest performing salmon in Scottish Sea Farm’s broodstock, and run by Norwegian company AquaGen.

Previously, eggs in most of Scotland’s salmon farms came from Norway, where AquaGen has long been Scotland's key supplier, but fears over the spread of infectious salmon anaemia through the eggs led to a temporary ban on importing eggs from the country, where there have been outbreaks in broodstock. 

My tour around Barcaldine began in a part of the building where alevin, tiny fish with yolk sac attached, are reared in conditions of near darkness that simulate their wild habitat.

“In the wild their mortality at this stage is 98%,” said hatchery manager Carlota Castaneda-Cobo, “but here at the hatchery they have an over 90% survival rate.”

Later, after passing through biosecurity measures, we watched parr swimming in cylindrical tanks, occasionally leaping across the surface. “The fish tend to shoal together, perhaps it feels safer,” said Ms Castaneda-Cobo, observing that one of the welfare criticisms often centres on stocking density. “Even when there’s lots of room, they tend to do this.”

Scottish Sea Farms is also called Norskott Havbruk and is owned by two of Norway’s biggest salmon companies, Salmar and Leroy.

Don Staniford, one of the most vocal campaigners against what is a global industry, said that 99% of Scottish salmon companies are foreign-owned, many of them by Norwegian companies.

He added: “Salmon farming is a welfare nightmare, inherently unsustainable.”

What is happening at Barcaldine is part of a new approach to salmon industry sustainability. The company is hoping to take contained salmon farming to the next level with a post-smolt farm, either on land or sitting in the sea close to shore, that will extend the period the fish are in a more controlled environment before they go out to farms..

But, even with all this innovation, is a truly sustainable industry possible?

Anderson is positive about its potential.“We’ve got some farms farming for 30-odd years in the same location,” she said. “The Brundtland Commission definition of sustainability is the ability for the next generation to be able to do it. You’ve got actual physical proof.”