Here, we present an extended version of a semantic model for overall welfare assessment of Atlantic salmon reared in sea cages. The model, called SWIM 2.0, is designed to enable fish health professionals to make a formal and standardized assessment of fish welfare using a set of reviewed welfare indicators. SWIM 2.0 supplements SWIM 1.0, which was designed for application by fish farmers. We searched the literature for documented welfare indicators that could be used by fish health professionals. The selected indicators are eyes, cardiac condition, abdominal organs, gills, opercula, skeletal muscles, vaccine-related pathology, aberrant fish, necropsy of the dead fish and active euthanasia. Selection criteria for the SWIM 2.0 indicators were that they should be practical and measureable on salmon farms by fish health professionals and that each indicator could be divided into levels from good to poor welfare backed up by relevant scientific literature. To estimate each indicator's relative impact on welfare, all the indicators were weighted based on their respective literature reviews and according to weighting factors defined as part of the semantic modelling framework. This was ultimately amalgamated into an overall SWIM 2.0 model that can be used to calculate welfare indexes for salmon in sea cages, taking into account the available fish health expertise. Using this model, an example calculation based on recordings and samplings done from an Atlantic salmon sea cage containing 106 000 fish yielded an overall welfare index of 0.81 of a maximum of 1.0.
This retrospective descriptive study estimates cage‐level mortality distributions after six immediate delousing methods: thermal, mechanical, hydrogen peroxide, medicinal, freshwater and combination of medicinal treatments. We investigated mortality patterns associated with 4 644 delousing treatment of 1 837 cohorts of farmed Atlantic salmon (Salmo salar) stocked in sea along the Norwegian coast between 2014 and 2017. The mortality is expressed as mortality rates. We found distributions of delta mortality rate within 1, 7 and 14 days after all six delousing treatments, using mortality rate within 7 days before treatments as baseline. The results show that we can expect increased mortality rates after all six delousing methods. The median delta mortality rates after thermal and mechanical delousing are 5.4 and 6.3 times higher than medicinal treatment, respectively, for the 2017 year‐class. There is a reduction in the delta median mortality for thermal and freshwater delousing from 2015 to 2019. There is a wide variability in the mortality rates, in particular for thermal delousing. Our results suggest that the variability in delta mortality for thermal delousing has been reduced from the 2014 to 2017 year‐class, indicating an improvement of the technique. However, a significant increase in the number of thermal treatments from 14 in 2015 to 738 in 2018 probably contributes to the overall increased mortality in Norwegian salmon farming.
The present study investigated the operational feasibility of the recently developed Salmon Welfare Index Model (SWIM 1.0) designed for Atlantic salmon (Salmo salar L) in production cages. Ten salmon farms containing spring smolts were visited twice, first between May and June the first year in sea cages, and secondly 2-3 months later. On each farm the SWIM 1.0 assessments were carried out for the two cages assumed by the farmer to represent the best and worst welfare status. The applied welfare indicators (WIs) were water temperature,
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