Scottish salmon farmer reduced fish mortality rate by 41% last year
Cooler seas, home-bred stock, adapted diets, vigilance, and enhanced treatment capacity all helped SSF achieve 90% survival
Salmon producer Scottish Sea Farms has reported a 41% reduction in fish mortality in 2024 compared to the year before, when warmer seawater temperatures caused challenges for the whole of the Scottish sector.
SSF said in its newsletter, The Source, that survival rates returned to historically high levels, up to 90% from 82% in 2023.
As previously reported, last year’s harvest volume increased to 40,400 gutted weight tonnes from 24,900 gwt in 2023.
SSF said its breeding programme, which is carried out in conjunction with AquaGen Scotland and uses broodstock selected from the company’s farms for their robustness, was key to the improved performance.
Resilient stock
“It takes three years to get fish up to broodstock size and the first crops from these fish, harvested in 2024, did really well. Every year we’re selecting fish from our farms which will then be used for broodstock. Hopefully, by doing this over successive generations, we will see even more improvement in the climate resilience of our fish,” SSF’s head of fish health and welfare Ralph Bickerdike told The Source.
Diets have also been altered to help meet the seasonal nutritional requirements for fish health and welfare.
“We worked with our feed supplier to adapt the composition of the feed in Q3, when fish health is most likely to be compromised, and the early results are very encouraging,” said Bickerdike.
When harmful jellyfish and plankton were detected at sites, temporary feed withdrawal was used to keep fish away from the surface where the threat was at its worst.
Biomass cameras
Technological advances also enabled earlier detection of disease and quicker interventions, added Bickerdike.
“We’ve been evaluating the latest underwater biomass cameras, which monitor individual fish for weight estimation and assess the condition of the fish without us having to handle them. They can give us real-time indications of welfare parameters, which we can then investigate and act on if necessary,” he explained.
Two wellboats contracted by Scottish Sea Farms last year have also helped reduce mortality. Each vessel is fitted with reverse osmosis for freshwater treatments and FLS delousing systems, allowing fish to be treated for amoebic gill disease (AGD) and sea lice at the same time, reducing the need for fish handling and thus improving fish welfare.
Bigger pens
SSF’s mainland regional production manager Innes Weir told The Source that the combination of the extra resources, lower lice levels and reduced jellyfish presence last year, plus cooler water, “allowed our fish to recover, survive, and grow”.
“We now have more understanding of what works and what doesn’t work. We took decisions to move some farms, within the same area but to more suitable locations with improved water exchange and better access for the wellboats,” said Weir.
“And we continued to upgrade farms with fewer but bigger pens - by April this year every farm in mainland Scotland will have moved to larger pens, with an average size of 120m. Going from 12 pens in a mooring grid to five creates a different hydrological dynamic around the farm that helps to promote growth and performance.”
Predator netting
Future improvements include increasing secondary predator netting for farms which have a higher risk of interaction with seals.
SSF will also do further evaluation of cleaner fish deployment; upgrade freshwater facilities; and collaborate with a new raft of R&D projects to help understanding of fish health and welfare issues.
“Not only did we come through last year with better survival, but we came through it with zero antibiotic use in our production farms,” said Bickerdike.
“We have become better at sharing best practice across our farming estate, with farm managers and support services meeting weekly to review fish welfare and biological performance. It’s an important gathering of information that allows us to look ahead. It doesn’t mean something won’t come out of left field, but we’re in a very much better place to meet challenges now.”
