The Marine Predation, Migration, and Habitat Use of Inner Bay of Fundy Atlantic Salmon (Salmo salar) Kelts

Abstract

Atlantic salmon (Salmo salar) populations have declined across much of their range, and the inner Bay of Fundy (iBoF) population has experienced one of the most severe collapses in North America. Despite supplementation-based recovery efforts restoring juvenile freshwater abundance, the number of adults returning to spawning rivers remains critically low and repeat spawners are largely absent, indicating that poor marine survival is hindering population recovery. Using temperature-sensing acoustic transmitters, this thesis examines the marine predation, migration, and habitat use of captive-reared iBoF Atlantic salmon kelts (post-spawned adults) to better understand the marine ecology of this critical life stage. Chapter 2 evaluates the role of predation in kelt marine mortality. Predation was observed in ~ 37% of iBoF salmon kelts detected in the Bay of Fundy (BoF). Neither fish size (total length; m) nor fish sex significantly influenced predation risk, but distinct spatial and temporal patterns of predation were evident, with events occurring predominantly during late spring and summer in the outer BoF. Thermal signatures indicated that most predation events were attributable to mesothermic predators, with limited evidence of marine mammal predation. Chapter 3 characterizes marine migration and seasonal habitat use of iBoF salmon kelts within the BoF. Seasonal modelling revealed increased kelt presence in the middle and outer BoF during late spring and summer, with spatial use shifting across months and concentrating in regions previously identified as important marine habitat. Kelts exhibited variable movement patterns, including both prolonged residency within the BoF and streamlined exits into the Gulf of Maine. About one third of the kelts exited the Bay at least once, primarily in May and June. Collectively, these findings provide contemporary evidence that predation is a prominent driver of marine mortality for iBoF salmon kelts, and that both survival and marine movements vary across space and time. This work directly informs recovery planning for this endangered population, including improving understanding of factors influencing marine survival, refinement of hatchery release strategies, and progress towards identifying important marine habitat for iBoF salmon kelts.