Food web incorporation of marine-derived nutrients after the reintroduction of endangered inner Bay of Fundy Atlantic salmon (Salmo salar)

Inner Bay of Fundy Atlantic salmon (Salmo solar) are endangered anadromous fish that have the potential to provide marine-derived nutrients (MDNs) to freshwater ecosystems depending on their population abundance. Salmon have been reintroduced to the Upper Salmon River, but not to the adjacent Point Wolfe River, in Fundy National Park, New Brunswick, Canada. This study determined whether stocking of adult salmon increased the productivity of the river. To examine the incorporation of MDNs, biofilm, leaf litter, Perlidae, Heptageniidae and brook trout (Salvelinus fontinalts) were sampled pre- and post-spawning in 2015-2017 from down- and upstream of a natural barrier in both rivers and analyzed for carbon (delta C-13) and nitrogen (delta N-15) isotopes. After salmon spawning in each year, all organisms at the downstream site of the stocked river increased in delta C-13 and delta N-15, with the greatest enrichment in brook trout (delta C-13: -23.97 parts per thousand to -21.10 parts per thousand, delta N-15: +6.36 parts per thousand to +10.73 parts per thousand). The proportion of MDNs in brook trout after salmon spawning (2015: 23.4%, 2016: 40.7%, 2017: 37.4%) also increased with higher numbers of released adult salmon. Results support the importance of salmon restoration for increasing the proportion of MDNs and productivity in rivers in Atlantic Canada.