AEI prepress abstract   -  DOI: https://doi.org/10.3354/aei00459

ABSTRACT: Planktonic salmon lice Lepeophtheirus salmonis salmonis larvae produced at salmon farms spread to and infect both wild and farmed salmonids. Understanding and forecasting the production and distribution of these larval stages from farms is critical to aquaculture management. However, model forecasts are based on available data and therefore include parameters with limited empirical support. This investigation examined salmon lice fecundity with a focus on batch egg clutch size by collecting lice from farmed Atlantic salmon Salmo salar at multiple farms and from wild Atlantic salmon and sea trout Salmo trutta captured at field sites throughout Norway. The data were analyzed with mixed effects models and total length of female lice was identified as the primary determinate of clutch size. Further analysis reveals that the total length is partially explained by temperature at sampling. However, if the temperature at sampling is spatially or temporally disconnected from rearing temperature it may not be possible to predict the total length of a louse from temperature. The fecundity investigation further found that 66% of the female lice on farmed salmon were sexually mature and 10% of those were not egg-bearing. In comparison, 73% of the adult female lice on sea trout were sexually mature and 40% of those were not egg-bearing. Our results indicate that salmon louse production forecasts would be improved by incorporating female louse sexual maturity and a clutch size parameter that is related to total length of female lice.