Nearby farms are a source of lice for wild salmonids: a reply to Jansen et al. (2016)

Abstract

Jansen et al. (2016; Aquacult Environ Interact 8:349-350) question the regression analysis presented in Serra-Llinares et al. (2014; Aquacult Environ Interact 5:1-16), which correlates lice abundances on farmed and wild fish. Jansen et al. (2016) argue that the correlation might not reflect a cause–effect relationship but be instead a mere artifact of the spatio-temporal covariance in lice abundance on farmed and wild fish driven by temperature. In this Reply Comment we revisit the analysis presented in Serra-Llinares et al. (2014) and further re-analyze our data following the statistical approach used by Helland et al. (2015; Aquacult Environ Interact 7:267-280), to rule out the potential confounding effect of temperature. We conclude that Jansen et al. (2016) were correct in conveying part of the observed correlation to the effect of temperature; however, there is solid evidence of a significant influence of lice originating from nearby farms on the observed lice abundances on wild fish, even after the effect of temperature is accounted for.