The Fish-iTrends database contains weekly counts of Lepeophtheirus salmonis and delousing treatments applied to Atlantic salmon aquaculture sites. This longitudinal repeated measures dataset provides the opportunity to estimate the effects of infestation pressures (a measure of the dose of exposure of parasitic stages of sea lice to potential fish hosts) adjusted for delousing treatments in the Bay of Fundy, New Brunswick, Canada, using a time-series model.
The sampling counts for 2016-2021 were aggregated to the site-level at weekly intervals (n = 3,137). These data were used to construct a mixed autoregressive model (AR[2]) for the abundance of adult female (AF) lice. The infestation pressures within and among sites were calculated as the time-lagged weighted averages of the abundance of sea lice. Treatment effects were evaluated by categorizing into short-term (chemical and mechanical) and prolonged treatments.
The infestation pressure of AF within sites was non-significant (p > 0.5); its effect was absorbed by the autoregressive function. The infestation pressure among sites (external infestation pressure), however, was shown to increase the abundance of AF by a factor of 1.28 (i.e., a relative increase of 28 % per unit increase of the variable) when other predictors remained constant (p = 0.002). For example, the closest sites by seaway distance contributed the most to the external infestation pressure of the selected site (Figure 1). This study provides further evidence that sea lice transmission occurs among the interconnected aquaculture sites in the Bay of Fundy.