The impacts of open net salmon farming on wild fish and their environment. Summary

Due to increasing resistance to chemicals traditionally used to treat sea lice infestations, the salmon farming industry has in recent years focused on the use of cleaner fish to consume lice when stocked in salmon pen; however, serious concerns have emerged around the potential overharvesting of these species from the wild and the poor welfare they experience. [...] Life cycle analysis of salmon farming shows that the production of fishmeal, fish oil, and the highly processed plant protein and fats that are also included, can constitute more than 90% of the greenhouse gas emissions from salmon farming and have the biggest impact on the sustainability of the harvested salmon. [...] The level of infection pressure also relates to the stage of production, with a higher weight of salmon on the fish farm, and the second year of two-year salmon production cycles associated with higher rates of sea lice on sea trout (Middlemas et al, 2010; Middlemas et al., 2012). [...] It is also worth noting that many of the drugs used to treat sea lice also have a withdrawal period, which means that salmon cannot be treated for a certain number of weeks leading up to harvest to ensure that the level of pesticides in the salmon sold to consumers is below a threshold set by food safety authorities, meaning sea lice are allowed to proliferate in the weeks immediately prior to har. [...] An overview of the sea louse reporting and treatment thresholds imposed in major salmon farming nations, and the standards set by the intergovernmental organisation the North Atlantic Salmon Conservation Organization (NASCO) for all nations to work towards, in order to limit the spread of sea lice between farms and into wild Atlantic salmon populations (NASCO, 2016; Zalcman et al., 2021).