Pollution from fish farm effluents increases in-river mortality of adult Atlantic salmon prior to spawning

No abstracts are to be cited without prior reference to the author.

Fish farm effluents released in rivers are point sources of pollution which perturb lotic ecosystems. They are known to have an impact on the production of Atlantic salmon (Salmo salar) juveniles. They may have an effect on Atlantic salmon adults before spawning as well. This hypothesis was assessed on the R. Scorff (Brittany, France), a small coastal stream on which a major trout farm is located. A previous study allowed to identify the zone impacted by the fish farm pollution. Using radio-tracking data before the spawning season, the (non-fishing) mortality of salmon adults which entered this zone was compared with that of fish who stayed downstream, where the influence of the source of pollution is considered to be negligible. The Bayesian treatment of a generalized linear model revealed that pollution from fish farm effluents caused a significant increase in the pre-spawning mortality of salmon adults. Consequences of this result on the renewal of Atlantic salmon populations are briefly discussed.