Ontogenetic Patterns in Body Stoichiometry Drive Element-Specific Cross Ecosystem Flux Rates in Atlantic Salmon Populations of Newfoundland, Canada

Migratory animals regulate trophic and biogeochemical dynamics of ecosystems by assimilating, transporting, and releasing nutrients at ratios and rates determined by their life history, elemental composition, and population size. We quantified whole-body elemental composition of three migrating life stages of wild Atlantic salmon from three Newfoundland watersheds to estimate the release of elements by salmon during spawning migrations and to assess patterns in net element flux between marine and freshwater ecosystems over 20-40 year periods. We found that smolts and kelts migrating downstream had similar elemental composition, which differed strongly from adults migrating upstream. Using differences in nutrient content of kelts and adults, we estimated nutrient releases by adults according to length. In our study systems, we estimated that adult Atlantic salmon that survive spawning and overwinter residence release 70-80%, 70-50%, and 20-30% of body carbon, nitrogen, and phosphorus in freshwater ecosystems, respectively. The remainder of each element returned immediately to the marine ecosystem within kelts. Release rates resulted in element dependent long term source-sink patterns. Populations in our study were generally net sources of carbon and nitrogen, but net neutral for phosphorus. Rapid changes to this pattern were associated with changes in marine ecosystem management occurring during study periods.