Hatcheries Disrupt Maternal Effects on Stable Isotope Signatures of Atlantic Salmon

Anadromous salmonids transmit isotopically enriched marine-derived nutrients to their offspring via the egg, but for how long these maternal signatures persist among juveniles or isotopic shifts may be disrupted by hatchery rearing is unclear. We employed stable isotope analysis of carbon (δ¹³C), and nitrogen (δ¹⁵N), as well as C:N ratios to assess the persistence of maternally-derived marine isotopic composition in Atlantic salmon planted as eggs in the wild compared to conspecifics reared under hatchery conditions.  Salmon alevins showed isotopic enrichment in ¹³C and ¹⁵N relative to the naturally occurring freshwater environment while they were still dependent on the maternally-derived yolk sac, but these became progressively depleted with the onset of exogenous feeding in the wild. In contrast, alevins reared in the hatchery maintained ¹³C- and ¹⁵N-enriched isotopic values derived principally from feeds throughout alevin development and into the first summer, resulting from feeding on fish oil-rich diets. Our results indicate that maternal effects can greatly influence the trophic ecology of Atlantic salmon and that trophic shifts from maternal isotopic signatures to freshwater-derived nutrients can be disrupted by feeding in hatcheries.  This makes SIA a simple tool for distinguishing hatchery-fed salmon from naturally occurring fry in the wild.