Salmon aquaculture elevates Atlantic salmon eDNA, but not pathogen eDNA across First Nations’ territories in the Broughton Archipelago

Pacific salmon landings have declined in British Columbia (BC) driven by stressors including climate change, habitat destruction, and infectious disease. Salmon aquaculture may hinder recovery by amplifying salmon pathogens in the environment. The Broughton Archipelago hosted intensive aquaculture production until several Indigenous-led initiatives resulted in the removal of most farms. Now, only three farms remain in Clio Channel, an area of overlapping territorial claims by Mamalilikulla First Nation (MFN) and Tlowitsis First Nation. In collaboration with MFN, we evaluated if eDNA from Atlantic salmon and several common salmon infectious agents (IAs) were elevated in tidal water flowing from Clio Channel into Knight Inlet. We found significantly greater concentrations of Atlantic salmon, but not IA eDNA, in Clio Channel compared to Knight Inlet, and detected Atlantic salmon eDNA up to 5.2 kms from the nearest source farm. Our research highlights that some eDNA has potential to disperse from salmon aquaculture in Clio Channel into Knight Inlet. We highlight the complexities of managing salmon health in shared territories with different approaches to salmon farming.