Much improved fish health and biology for Mowi Scotland in 2024 - MOWI - Scotland

Much improved fish health and biology for Mowi Scotland in 2024

Bubble Curtain

A good performance for Mowi Scotland in 2024 with significant improvements in salmon health, welfare and performance.

The year saw a 35% reduction in overall biomass mortality across all seawater farms compared to the previous year, and 45% reduction when mortality is expressed in terms of individual fish numbers. This great achievement is a testament to the collective effort of the Mowi Scotland farming teams.

What drove such a significant improvement? Both Health and Production teams worked relentlessly to address health challenges and mitigate environmental stressors experienced in previous years and refined strategies, enhanced biosecurity and implemented innovative solutions, all with a strong emphasis on prevention. Essentially this was combined with more favourable climate conditions in 2024, including slightly cooler temperatures and abundant rainfall in the summer.

Mortality rates in salmon farming came under ever more scrutiny from outside stakeholders in our sector and, whilst we welcome this interest, it is important to note that environmental challenges remain the main cause of mortality in our stocks. The only thing that will improve this is investment; the best people and their skills and a relentless focus on adaption and innovation.

Outlined below are key areas that have contributed most to the success of 2024.

Vaccination

Mowi Scotland continues to advance rapidly in preventive health strategies. Since 2022, the company has introduced one new vaccine per year, which we believe has contributed significantly to the improved biological outcomes observed in 2024. These autogenous vaccines, developed in collaboration with Ridgeway Biologicals, are created from bacterial isolates collected and characterised from our sites.

The first vaccine, fully implemented in 2023, targeted Pasteurella skyensis, a pathogen responsible for clinical outbreaks on some farms over the past decade. Since its introduction, while the bacteria has been detected in the environment, clinical signs have been minimal, and no outbreaks have occurred. Building on this success, the vaccine was enriched with new antigens to protect against Yersinia ruckeri. Following rigorous safety testing, this enhanced vaccine was introduced in early 2024, with very promising results.

We are now developing the third generation of the vaccine, set for deployment in 2025. Additionally, our salmon are protected by other licensed vaccines against a broad spectrum of pathogens, including pancreas disease (PD), furunculosis caused by Aeromonas salmonicida, IPN, and Moritella. Vaccination is at the core of our preventive health strategy, and we continue to explore new solutions to safeguard our fish, particularly against the emergent Piscirickettsia salmonis, which causes Salmonid rickettsial septicaemia (SRS).

Biosecurity

An essential preventive strategy is biosecurity throughout our operations from egg to harvest. Our fleet of boats employ the latest technologies for water filtration, reverse osmosis to make freshwater for parasite control and disinfection through ozonation. Through strict biosecurity barriers, our fish health professionals, boat crews and site staff work diligently to ensure pathogens are under control, safeguarding salmon stocks. This is no simple task as pathogens are naturally present in the environment. Biosecurity requires meticulous attention to every stage of production from disease free egg input into our hatcheries, recirculation systems in our freshwater operations, equipment and fish handling, to transport lorries, vessels, treatments, feeds and harvest.

New tools in development such as bacteriophage therapy could revolutionise our biosecurity measures. Phages are viruses that target and kill bacteria, they are highly specific to bacterial strains, abundant in nature and safe to use. They replicate as long as their host bacteria are present, rapidly reducing pathogen loads in the water. Bacteriophage therapy is regarded as a promising solution to antimicrobial resistance, both in human and animal health, and would contribute significantly to reducing the use of antibiotics in farming. While one such product is already on the market, its use currently depends on regulatory frameworks being established in the UK.

Mowi Scotland is at the forefront of developing phage therapeutics with a co-funded PhD project in collaboration with the University of Exeter which has several applications throughout the salmon production cycle. This highlights the company’s commitment to advancing innovative research in this critical area. We hope bacteriophage will soon become a reality in salmon farming.

Parasite control

FLS Mechanical Delousing

Pest control for both sea lice and Amoebic Gill Disease (AGD) saw significant improvements in 2024, contributing substantially to the year’s positive outcomes. Sea lice levels reached their lowest in more than a decade, and mortality linked to AGD and other gill infections was reduced by 56%. Additionally, medicine usage for bath treatments was cut by 60% in 2024.

This success was driven by major investments in non-medicinal solutions. Three well boats are equipped with reverse osmosis systems to produce freshwater for AGD treatment, FLS mechanical delousing to gently remove sea lice after freshwater baths, and ozonation systems to maintain pathogen-free vessels. Importantly, our in-house AGD diagnostic plays a critical role in monitoring parasite pressure and treat in a timely fashion.

Cleaner fish, an essential part of our pest management strategy, also played a crucial role in controlling sea lice in 2024, further supporting the health and welfare of our salmon. And we are continuously seeking to improve this biological control method which minimises salmon handling.

Jellyfish

Bubble Curtain

In recent years, Scottish waters have experienced an increase in harmful plankton species, including well-known phytoplankton, as well as jellyfish, mainly micro jellyfish species like Muggiaea atlantica and, more recently, deep-water Apolemia species, also known as string or barbed wire jellyfish. While these species are not new to the West Coast of Scotland, their prevalence has increased and our staff monitor prevalence and species daily on all our seawater farms. Upon contact with salmon, they release stinging cells that cause skin and gill damage and potential secondary infections.

Mitigating these impacts has been a key focus in 2023 and 2024. Although moving fish out of affected areas is the most effective strategy, it is not always feasible or recommended due to biosecurity risks. Alternative measures have been implemented or are under development, such as feed withdrawal to prevent fish from swimming near the water surface where plankton and jellyfish concentrations are highest, as well as the use of aeration systems. These methods have proven successful in protecting salmon and maintaining stock health.

In 2024, new technologies were tested for the first time in Scotland with promising results. One such innovation is the bubble curtain, which acts as a physical barrier against plankton. Already used successfully in other Mowi business units against phytoplankton blooms, including Chile and Canada, bubble curtains have now demonstrated their effectiveness also against micro jellyfish in Scotland. Other measures, such as deep-welling aeration, are also being explored, though they are less applicable in Scotland’s relatively shallow waters.

New developments to enhance robustness, welfare, fish health and ultimately performance

Mowi hatchery

Two strategic developments were launched in 2024 to strengthen salmon farming in Scotland. The first is a new Scottish-based breeding programme aimed at producing more robust stocks to conditions experienced in Scottish waters. Following pilot-scale testing in 2023, Mowi Scotland successfully produced 20.5 million green eggs at a commercial scale in 2024, using Mowi salmon strains. This achievement reflects the exceptional efforts of the new broodstock team. Plans are in place to scale up production further in 2025 with the opening of a state-of-the-art breeding facility by summer in Ardessie, expected to drive significant improvements in fish health and performance.

Our new breeding facilities will use the latest recirculating aquaculture system (RAS) technology to enable use of temperature and photoperiod regimes to produce early and late season eggs, a key element of Mowi’s freshwater smolt production plan. We expect the new farm will produce up to 50 million eyed eggs of Mowi strain to supply our production hatcheries, ensuring Mowi Scotland becomes self-sufficient in eggs supply. Mowi genetic strain consistently shows better performance and survival in Scottish waters. With the support from Mowi geneticists using DNA analyses, broodstocks will be further selected for enhanced performance and health phenotypes to thrive in Scottish farming conditions. Significant improvements in stock robustness are expected over the coming years especially for prevalence and severity of cardiomyopathy, gill health, overall disease resistance and tolerance, and other performance traits.

Loch Etive

The second major initiative in 2024 was the launch of a new post-smolt strategy in Loch Etive, with the first cohort successfully transferred in the autumn. These fish are soon to be harvested after less than 12 months at sea from smolt. Larger smolts entering the sea spend less time in open waters, reducing exposure to health risks such as planktonic blooms. Unlike many countries that rely exclusively on land-based facilities for post-smolt rearing, Mowi is leveraging Scotland’s brackish-water lochs. These provide a sheltered, lower-risk environment naturally protected from jellyfish and harmful algae, offering salmon a safer start before they transition to the sea.

While 2024 delivered excellent results, further progress is needed to meet Mowi’s ambitious goal of reducing mortality at sea. To this end, Mowi Scotland has embarked upon a new five-year project with the University of Edinburgh to further build the scientific knowledge underlying salmon robustness and develop new tools, innovations and talents to drive our commitment towards sustainability, welfare and performance. The BBSRC Business and Academia Prosperity Partnership project, SalmoStrong, will recruit four PhD students and four postdoctoral fellows to advance research across three key pillars to unlock the potential of new innovations and capitalise on recent Mowi investments. This includes seeking to understand the diversity of genomes, the impact of early rearing practices and developing novel characteristics to look for and select the most robust and resilient fish from the newly established breeding population.

Mowi Scotland team

There is a lot going on and this could not be done without the amazing skills and dedication of our staff throughout our operations. A special congratulation to the Mowi health team who lead on all health and welfare fronts together with the production team to safeguard the welfare and health of our salmon. Together they monitor and manage fish health on 59 farms on land, in lochs and at sea.

The Mowi Health team is made of 12 health professionals spread across Scotland

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