Describing temporal change in adult female Lepeophtheirus salmonis abundance on Scottish farmed Atlantic salmon at the national and regional levels

Patterns of change over time for adult female Lepeophtheirus salmonis abundance on Scottish farmed Atlantic salmon, Salmo salar, from December 2010 to September 2017 inclusive at the national level and four constituent regions are described. The analysis comprises a Generalized Additive Model on summary statistics published by the Scottish Salmon Producers' Organisation. Irregular within-year oscillations were detected at the national level and for three regions. Non-linear longer-term changes at the national level and for two regions were also detected with no apparent overall increase occurring over the period. The results from this analysis are compared to those from a previous analysis utilising a linear model on a subset of the data. We conclude that the GAM provides an improved description of the temporal changes of this parasite.