DeJong, Rachel2017-05-152017-05-152017-05-152017-05-11http://hdl.handle.net/10012/11891Many northern fishes display plasticity in life history and trophic ecology that can influence productivity of fisheries and bioaccumulation of contaminants, such as mercury. Cisco (Coregonus artedi), Lake Whitefish (Coregonus clupeaformis), and Northern Pike (Esox lucius) are important subsistence food fishes to Aboriginal communities on the west coast of Hudson Bay, and our understanding of the life history of these fishes is incomplete. In this study, I investigated life history and trophic ecology of Cisco, Lake Whitefish, and Northern Pike from three rivers of the Hudson Bay Lowlands. Fish of each species were classified as either non-migratory or migratory using otolith microchemistry profiles, and results indicated clear use of marine habitats by Cisco and Lake Whitefish. Whereas use of brackish-water habitats is well-documented for Northern Pike in the Baltic Sea, I present the first data indicating possible use of brackish habitats by Northern Pike in North America. The majority of Cisco (99 %) and Lake Whitefish (92 %) were classified as migratory, whereas the majority of Northern Pike (70 %) were classified as non-migratory. A mixing model (MixSIAR) applied to stable isotope ratios of sulphur (δ34S) was used to determine proportional dietary contribution of prey from marine and freshwater-derived sources for each fish species in each river. The majority of the diet of migratory Cisco (76 to 85 %) and Lake Whitefish (59 to 75 %) was composed of marine-derived nutrients/prey. Both migratory and non-migratory Northern Pike were reliant on marine-derived nutrients/prey. I estimated that up to 40 % of non-migratory Northern Pike diets were derived from marine sources; this is evidence that non-migratory Northern Pike were feeding on marine-derived resources (possibly anadromous Cisco and Lake Whitefish). Results of this study will enable better predictions of changes in species-specific life history due to climate-induced shifts in temperature and/or productivity in northern rivers and oceans. In combination with contaminant data, my results can be used to better understand how fish life history influences contaminant bioaccumulation both now and in the future.  enlife historymigrationsNorthern PikeCiscoLake WhitefishHudson Bay LowlandsMaster Thesis