Predation effects on juvenile Atlantic salmon (Salmo salar) populations in changing riverscape

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Natural processes, such as predation, are at play in all populations. Different anthropogenic actions (e.g. fisheries management, hydropower, climate change) may alter the effect that Atlantic salmon (Salmo salar) populations realize due to predation pressure. With many A. salmon populations threatened, any human-induced change may be detrimental. The field-based research proposed herein focuses on assessing effects of predation on juvenile A. salmon under three case situations in natural-flow and flow-regulated rivers. The first project focuses on assessing a proposed trap-and-truck management strategy in a large hydropower regulated Saint John River (SJR), New Brunswick (NB). Our previous studies suggest late-autumn predation threat for pre-smolt A. salmon at the vicinity of a hydropower station. The validity of this hypothesis is examined by using novel predation-tag acoustic telemetry. Data on frequency and locations of predation events (from predation tags) will be combined with predator movement data from regular acoustic tags (striped bass Morone saxatilis and muskellunge Esox masquinongy) and the frequency of predation is examined as a function of water temperature. The second project focuses on assessing the predation threat of expanded ( >1 million) striped bass population on A. salmon smolts in the Miramichi River, NB. Project will quantify predation by different size categories of striped bass in time and space throughout the smolt migration window, and combine these data with the total daily run size of A. salmon smolts to reveal a potential predation threat by size category. The information will be used to revise fisheries management advice within bass fishery. The third project will A) compare seasonal levels of predation by semiaquatic mammals in wadable streams with contrasting ice-regimes (i.e. ice-free and ice covered) and B) examine the established hypothesis that threat of predation is the driving force of cessation of daytime activity in cold water temperature in juvenile A. salmon. Both research components rely on new developments in Passive Integrated Transponder technology for tracking juvenile A.salmon. Field research for project P3A will be undertaken in small streams in NB where ice processes are known based on previous research. Project P3B will occur in the Kapisillit River in Greenland; the only stream in the world where an A. salmon population has evolved in the absence of mammalian predation. Winter behavior of A. salmon is therefore expected to reflect different activity patterns than in populations where winter predation has evolutionarily been present. The proposed research will contribute novel information regarding the role of predation in regulating A. salmon populations in seasonal small nursery streams in changing climate, and will provide advice that is directly applicable for better managing threatened and socio-economically important A. salmon populations in significant North American salmon rivers.