Impacts of salmon farming on Atlantic cod stocks Salcod

Fishermen have repeatedly claimed that salmon farms prevent Atlantic cod from using their traditional spawning grounds, and that this causes diminishing coastal cod populations. In the current project, impacts of salmon farming on cod stocks, we aim to get a holistic view of the impact of salmon farming on wild cod populations. To achieve this, despite Corona challengers, we have captured, acoustically tagged and released between 50-100 large spawning cod during winter, as well as around 50 larger coastal cod during autumn, annually since 2019. Migratory behavior and home range of these have in detail been investigated through a network of listening hydrophones, which also have been maintained continuously for the last foure years (WP 1). We have also captured, sampled (e.g. to discriminate between Coastal and North East Arctic Cod), tagged and released more than 5000 juvenile cod. These will give us information about abundance, growth and behavior in young cod (WP 2). Physiological effects (e.g fatty acids and growth) in cod close and distant from fish farms (WP 3), as well as how cod uses sea floor and benthos, and how this again is influenced by intensive salmon farming activity (WP 4), have also been studied. In addition, we have reviewed the literature (submitted article) on effects of salmon farming on marine fish, including ongoing Norwegian research on cod. In the recently published article «Movement diversity and partial sympatry of coastal and Northeast Arctic cod ecotypes at high latitudes», we have shown that migratory pattern of NEA- and Cosatal cod is more variable than earlier believed – NEAC also tend to stay inside the fjords, while a large proportion of Coastal Cod leaves the fjords. This, together with new analyses on growth and liver fatty acid composition (submitted article), will be the fundament for updated risk advice and will be published in the next IMR report on “Environmental effects of Norwegian fish farming” (WP 5). By implementing a before-after-control-impact (BACI) study design, working in northern Norwegian fjords with and without, but also by repeating the investigations above after establishment of a salmon farm, we hope to quantify the impact of salmon farms on cod survival, growth, migration, spawning and recruitment, and collate this in models, allowing us to make broad inferences about the underlying mechanisms and identify the pressures from salmon. Altogether, this will merge into improved advice to government, industry and population about how to secure aquaculture growth concurrent with preservation of wild fish and sustainable fisheries (WP 5 and 6). Establishment of the planned salmon farm in Frakkfjord have however been delayed, although the integrated coastal zone planning activity still continues, and might open for a future farming permission. In accordance with the Norwegian Research Council (NRC), the NRC-project has therefore been temporary put on hold in parts of 2022, and thereafter turned more towards a comparative study between Frakkfjord and the intensively farmed Langfjord: In autumn 2022 also Langfjord was acoustically instrumented, and we have tagged close to 1000 small cod, including more than 100 with acoustic tags during winter, and another 100 during autumn 2022 and 2023. If the farm is further delayed, or do not come at all, this will give us valuable comparable cod-data in a fjord with- and without salmon farms and ensure as good as possible achievements of the project. During November/December 2023, alle loggers were removed from both fjords and data downloaded. The last year will be dedicated to analyzing and compilation of the results, but research will continue within the new strategic IMR “CoastNorth” program.

There are more than 1000 operational salmon farms along the Norwegian coastline, typically situated in fjords and often overlapping with the habitats of commercially and culturally important wild species. Despite the vast volume of salmon aquaculture in Norway, the full scope of its ecological impact is yet to be thoroughly investigated. In the proposed project, Impacts of salmon farming on Atlantic cod stocks (‘SalCod’), we aim to get a holistic view of the impact of salmon farming on wild Atlantic cod Gadus morhua populations in the Arctic region. To achieve this, we will use a suite of different approaches, including acoustic telemetry, mark-recapture studies, diet, growth- and maturation schedules and detailed examinations of juvenile habitat utilisation and associated benthic community structures. We will implement a before-after-control-impact (BACI) study design, working in northern Norwegian fjords with and without, and before and after, salmon farming over a five-year period. We will be able to quantify the impact of salmon farms on cod survival, growth, migration, spawning and recruitment, and collate this information in IBM and state-space models, allowing us to make broad inferences about the underlying mechanisms and identify the pressures from salmon farming on cod populations, how they vary interannually and upscale the results to the population level. This is at the heart of the Marinforsk Call.