Experiences from targeted removal of farmed Atlantic salmon from Norwegian rivers

Abstract

Farmed salmon escaping from aquaculture and interbreeding with wild conspecifics pose a significant threat to the genetic integrity of natural salmon populations. Despite advancements in aquaculture security, escape incidents persist, prompting the need for effective mitigation strategies. This study summarizes experiences from efforts to remove escaped farmed salmon over a 12-year period in 63 western Norwegian rivers, using either (1) spearfishing during snorkelling by trained personnel or (2) traditional fishing methods employed by local groups. Recaptured farmed salmon ranged widely in size and included both spawners as well as immature fish, demonstrating that farmed fish entering rivers comprise fish of different ages and escape histories. Traditional fishing by locals recaptured the highest number of farmed fish, while removal during snorkelling in general captured larger and mature fish. On average, 53% of the farmed salmon observed during snorkelling were recaptured. This efficacy was influenced by the number of farmed fish present and the size of the farmed fish. In addition, efficacy increased over time, indicating that the removal team became more efficient. The study underscores that active removal, when executed judiciously, contributes to reducing the ecological risks associated with escaped farmed fish, complementing broader strategies for sustainable aquaculture.