Environmental Variability on Migration and Survival of Post-Smolt Atlantic Salmon

Atlantic salmon (Salmo salar) spawning returns to rivers continue to decline despite intensive restoration programs. Most management and research efforts have focused on freshwater life-stages and conservation of freshwater habitat. Little is known about the marine phase of post-smolts but recent work suggests a potential bottleneck at this life-stage. Dynamic modeling was used to examine growth and survival of post-smolts as they migrate through the Gulf of Maine to the Scotian Shelf. A coupled ocean circulation model and a bioenergetics model were used to explore post-smolt energetic costs during this migration over observed ranges of hydrographic variability. Preliminary results suggest inter-annual variability in environmental conditions may contribute to survivability and migration success. There is little variation in migration success across natal river populations despite extreme differences in the amount of time post-smolts spend swimming against strong coastal currents and potential predator and prey communities encountered. Currents and temperature gradients alone do not explain navigational behavior. Large-scale oceanographic conditions contribute to survivability of salmon. Coastal predator-prey interactions alone do not account for the high marine mortality. The model serves as a template on which we can examine climate change scenarios to evaluate relative importance of changing temperature and current conditions.