MEPS 610:191-203 (2019)  -  DOI: https://doi.org/10.3354/meps12841

ABSTRACT: The marine portion of Atlantic salmon Salmo salar L. life history is not well understood, with many populations exhibiting declines in survival and growth linked to changes in the food web. Atlantic salmon of North American origin feed along the coast of West Greenland from August to November and are exposed to a variety of different ecosystems and hydrographic and environmental regimes that affect marine food webs. Here we used stable isotopes to assess the reliance of Atlantic salmon feeding on inshore prey resources and its associated seasonal variation, and examine the correlations of varying inshore resource use with size, condition and trophic niche width. On average, Atlantic salmon relied on inshore resources for 38% of their diet (range of 0-84%). The reliance on inshore prey increased throughout the season, as did size and condition. Although differences between inshore and offshore feeding fish were small, the resulting implications of associated differences in size and condition on subsequent survival and spawning success suggest important biological consequences of feeding habitat choice. The variation in inshore resource isotope values mirrored hydrographic variation and associated changes in prey related to glacial input, frontal zones between inshore and offshore water masses and nutrient input from run-off. Increasing reliance on inshore feeding may be due to a high abundance of spawning capelin Mallotus villosus in the fjords. Omnivory was found to be highest in fish using both the inshore and offshore environments, suggesting a greater diversity of diet in these fish.

KEY WORDS: Atlantic salmon · Inshore/offshore feeding · Stable isotopes · Northwest Atlantic · Trophic niche