Acoustic telemetry reveals endothermic predation and post-spawning movements of Atlantic Mackerel (Scomber scombrus) in the Bay of Fundy

Canadian Journal of Fisheries and Aquatic Sciences, Volume 83, Issue , Page 1-17, January 2026. Atlantic Mackerel (Scomber scombrus) in Canadian waters have declined severely, yet limited understanding of predation risk and post-spawning movements constrains management and rebuilding efforts. We used >200 acoustic receivers across the Bay of Fundy and Passamaquoddy Bay (PB), Canada to track post-spawning behaviour of 70 tagged mackerel. Sixty-eight were detected, and six were confirmed predated based on transmitter temperature signatures > 30 °C, consistent with endothermic predators (pinnipeds, whales). No predation by mesothermic predators (e.g., sharks, tuna) was observed, and events occurred exclusively in outer PB during late summer, yielding a minimum natural mortality estimate of 0.09. Generalized additive models indicated strong residency and persistent use of inner PB into fall. Network analyses identified key corridors linking Deer and Campobello islands and Deer Island with St. Andrews, New Brunswick. Most individuals departed the Bay by early November, with some moving into U.S. waters as far south as Cape Cod, potentially exposing northern contingent fish to U.S. fisheries operating during this period. These results demonstrate basin-scale telemetry's value for resolving survival, movement, and connectivity, informing assessment and rebuilding of this collapsed stock.