The Influence of Shellfish Aquaculture on Abundance and Diet of Juvenile Pacific Salmon

High early marine mortality of juvenile Pacific salmon is thought to be a contributing factor to the decline of some salmon populations. It is therefore important to understand how nearshore nursery habitats, utilized by juvenile salmon, are influenced by anthropogenic activities such as shellfish aquaculture. Current shellfish farming practices modify nearshore habitat through the placement of anti-predator nets, intertidal fences and oyster rafts however, little is known about the effects of this additional structural complexity on habitat use by juvenile salmon. To investigate these influences, we quantified abundance, diet and the incidence of microplastic ingestion by juvenile Pacific salmon on beaches with active shellfish farms compared to ‘natural’ beaches in Baynes Sound, BC. Juvenile salmon were identified, enumerated and subsamples were euthanized for stomach content and microplastic analysis. Higher salmon abundances were found at shellfish farms compared to natural beaches. Major prey items for juvenile Coho and Chinook salmon included amphipods, copepods, decapods, terrestrial insects and fish. The most numerically abundant prey items for both species were decapods and insects while fish dominated diets in terms of mass. Further shellfish farm and natural beach comparisons are currently being conducted along with the potential drivers for the observed differences.