Farmed salmon is one of Canada's most valuable aquaculture exports, but concerns about the sustainability of salmon aquaculture have long been debated. Sea lice remain a significant challenge in British Columbia (BC) and other major salmon-producing countries worldwide. In BC, Fisheries and Oceans Canada (DFO) regulates sea lice management through licence conditions that require salmon aquaculture producers to maintain sea lice levels below established thresholds, particularly during the juvenile wild salmon migration season (March to June), and to implement mitigation measures when thresholds are exceeded. The objectives of our study are to summarize the extent of sea lice mitigation measures implemented across salmon aquaculture sites in BC, Canada and to assess and compare the associated mortality events for each mitigation strategy from January 2017 to June 2022. Under licensing conditions, salmon producers in BC must report both sea lice management actions and any associated mortality events to the DFO. In this study, treatments associated with mortality events were classified as cases, while those without such events were classified as controls. A mixed-effects logistic regression model was used to estimate the effect of each mitigation measure. Our results indicated an overall upward trend in the number of mitigation events per site per year, largely driven by the increased adoption of treatments involving fish handling. In-feed treatments were associated with significantly lower odds of mortality compared to delousing measures involving fish handling. Among treatments involving fish handling, such as mechanical removal, medicinal baths, and non-medicinal baths, there was no significant difference in the younger fish category; however, in adult fish, non-medicinal bath treatment had significantly lower odds of mortality than the others. Given the elevated mortality associated with mechanical removal and bath treatments, there is a need to develop and implement more sustainable sea lice management strategies to ensure the sustainability of salmon aquaculture in Canada. • Sea lice delousing frequency increased markedly in BC salmon farms between 2017 and 2022. • In-feed treatment was associated with substantially lower odds of treatment-related mortality events than mechanical removal and bath treatments. • No significant differences in treatment-related mortality were observed among fish handling delousing treatments in younger fish. • In adult fish, non-medicinal bath treatment had lower odds of mortality than medicinal bath and mechanical removal treatments.
Jyoti et al. (Fri,) studied this question.