Scottish salmon farm mortality, escape, fish health inspectorate and sea lice data is now available for early 2018. We’ve been going through this data, and have found the following…
- Mortality is slightly higher compared to last year
Overall, between January and March 2018, between 707,000 and 3 million fish (3534 tonnes) died on salmon farms in Scotland, which is slightly increased compared to the same time last year, when mortalities totalled 3258 tonnes by March 2017.
The greatest monthly mortality recorded was at the salmon farm Carradale (North), where an estimated 38,000 to 200,000 (192,508kg) salmon died in March. This was largely as a result of physical damage caused by stormy weather.
- Monthly mortality has already been as high as 27%
Looking into mortality as a percentage of biomass on site, you can see that monthly mortality has already been as high as 27% for one site- that means over a quarter of biomass was lost on one site within one month.
- Various diseases have already caused problems
Marine Harvest publish reports on mortality events, and these are available for January to March 2018. They show that sites have experienced problems with cardiomyopathy syndrome, a viral infection that causes infected fish to have reduced cardiovascular function, leaving fish weak, fragile and more susceptible to further stressors. Anaemia and Pasteurella skyensis, a bacterium which has previously caused large losses in Scotland, have also been documented to have caused mortality events on Marine Harvest sites in 2018.
- Fish health inspectors have reported seeing dead, weak or abnormally behaving fish
The fish health inspectorate (FHI) inspect salmon farms to check on fish health. Between January and March of this year, the FHI visited 15 seawater salmon farms. Of these 15, the FHI reported seeing dead, weak or abnormally behaving fish on 7 of these (47%).
Following the detection of these fish, on some visits diagnostic reports were carried out by inspectors. One of these diagnostic reports, at the farm Meall Mhor, included the description that the fins were in “very bad condition on all fish” with one fish also “missing part of the upper jaw” and another “missing one eye”. This damage was largely due to bad weather.
- 30% of sites breached sea lice trigger levels in January and February
SSPO data shows that in January 2018, of the sites that were stocked continuously throughout the month, 39 (31%) had average female lice levels of greater than 1, a level above recommendations set by the Code of Good Practise (CoGP). The highest recorded lice level in January was at the farm Trilleachan Mor, owned by the Scottish Salmon Company, which had an average female lice load of 7.13.
Trigger levels set by the CoGP are different for February, where an average of 0.5 adult female lice is the trigger for treatment. In February, 43 (32%) sites reported average lice levels that were greater than 0.5. The farm with the highest average lice load in February was Turness, owned by Cooke Aquaculture, with an average female lice load of 3.08.
Sea lice are a threat to the welfare of salmon as they feed on the flesh, tissue and scales of fish, leaving tissue exposed. This causes disruption to osmoregulation, leaves fish susceptible to further infection, and can lead to increased stress and mortality.
- There have already been 6 escape events
These 6 escape events led to just under 23,000 salmon escaping from salmon farms.
The site with the largest escape event was Loch Snizort, where 21,712 salmon escaped because of a hole in the netting. For the five other escape events, the causes of such escapes vary, and include equipment failure and human error.
Salmon that escape from fish farms have compromised welfare as they are no longer well adapted to life in the wild, so likely suffer. Escaped farmed salmon can also damage the health and welfare of wild populations, with research showing that escaped farm salmon can interbreed with wild individuals. This negatively impacts wild populations as it creates offspring that are poorly adapted to the wild environment.
 Assuming all salmon that died weighed 5kg
 Assuming all salmon that died weighed 1kg