A disease trap for wild and farmed salmon in British Columbia, Canada

Recent theory has shown that ecological and economic interactions between wild and farmed fish can result in unstable tipping points between a fishery-dominated versus an aquaculture-dominated coastal sea. In this Perspective, I argue that the essential features needed for such bistability are present for wild and farmed salmon in British Columbia (BC), Canada. Specifically, a disease trap is created by a feedback loop involving fisheries decline, incentives for aquaculture growth, and parasite transmission. Under these conditions, theory predicts that wild salmon populations can become trapped in a collapsed state by the pathogen community maintained in coastal seas by salmon farms. Importantly, it is not needed for pathogen transmission to be involved in the original cause of fishery collapse, which is considered to be multifactorial for wild salmon in BC. The theory is relevant to recovery efforts for wild salmon and policy on salmon aquaculture in British Columbia, for which a path can be charted that either entrenches or avoids a disease trap.