Spatiotemporally dependent relationship between salmon lice from salmon farms and infestation on juvenile Pacific salmon in British Columbia, Canada

This study examines the relationship between salmon lice Lepeophtheirus salmonis infestation pressure from Atlantic salmon farms and the prevalence of L. salmonis on wild juvenile Pacific salmon in British Columbia, Canada. We estimated weekly copepodids released from salmon farms and analysed infestation data from wild juvenile chum salmon Oncorhynchus keta and pink salmon O. gorbuscha across 4 regions from 2016 to 2023. A mixed-effects regression model revealed a significant positive relationship between farm-derived infestation pressure and L. salmonis prevalence on wild salmon at the sampling event level, with notable spatial and temporal variations. Chum salmon exhibited higher infestation rates than pink salmon, and fish length was positively correlated with infestation likelihood at the individual level. Our findings highlight the importance of accounting for fish length, environmental variables, and larval dispersal patterns to refine infestation pressure estimates. The complexities and uncertainties in quantifying infestation pressure underscore the need for further research. Future studies should validate underlying assumptions and incorporate additional variables and methodologies to improve assessments of infestation pressure on wild salmon populations.