Interactions between wild and farmed Atlantic cod: non-lethal impacts of escapees on wild populations

Cod is a new target species for aquaculture in the north Atlantic. With increasing numbers of farmed cod kept in sea-pens in coastal areas it is necessary to address the potential impacts of cod aquaculture on the local environment. Of particular concern is the effect of cod that escape from net-pens. The main risks that these escapees pose to native cod stocks are genetic alteration, competition for space and resources, disruption of social behaviour, transmission of pathogens and alteration of predation regimes. Genetic introgression from escapees has caused fitness depression in wild salmon populations and similar effects may be possible for cod. The impact of farm escapees does not necessarily depend on fish surviving to reproduction. If the escapee p opulation is continually replenished they may still have a deleterious effect on earlier life history stages. Hence, to understand fully and to avoid potential impacts of escapees on wild stocks, detailed information on how farmed fish compete and interac t with wild fish in both nursery habitats and spawning grounds is required. Results from stock enhancement research indicate that we can expect interactions at both juvenile and adult phases, as juvenile reared cod remain within a few kilometres from thei r release site and mature reared cod enter local spawning grounds. We will use a combined approach of laboratory and field experiments to test if escapees: compete for space and reduce the ability of local populations to avoid predators, disrupt spawning events and hybridise with wild populations. These experiments will be fundamental for understanding, predicting and avoid potential impacts of farmed escapees on coastal cod stocks.