Reversing decline: The impact of spatial conservation on endangered northern bottlenose whales

Abstract Despite the end of commercial whaling in 1972, the northern bottlenose whale ( Hyperoodon ampullatus ) remains endangered in Canada and faces multiple human threats. The effectiveness of marine protected areas (MPAs) in safeguarding highly mobile species like these whales is still unclear. We examined 35 years (1988–2023) of population trends in the Gully submarine canyon, off Canada's east coast and assessed spatial changes in human activities within protected and unprotected habitat on the Scotian Shelf. We analysed population size and habitat use using sighting rates and photo‐identification mark‐recapture data. We also evaluated whether spatial protections implemented through the designation of the Gully MPA in 2004 were associated with changes in the spatial distribution of threats, including ship strikes, entanglement, pollution and military sonar. We found the northern bottlenose whale population declined from 1988 until the mid‐2000s. However, from 2004 to 2010, coinciding with the establishment of spatial protections, this trend reversed, with the population growing near its maximum biological potential (~4% per year). Our analysis indicates that the intensity of two serious threats—commercial fishing and vessel traffic—has decreased within the highly protected Zone 1 area of the Gully MPA, where approximately 42% of the population can be found at any time. However, these activities now occur relatively more often in important habitat areas outside the MPA, indicating a spatial shift in fishing effort that raises concerns about potential displacement effects. Synthesis and applications . Spatial protection of the Gully MPA in 2004 coincided with a shift in human activities and the first signs of population recovery for northern bottlenose whales. While this suggests that well‐designed MPAs can contribute to conservation outcomes even for highly mobile species, long‐term success likely depends on continued monitoring and effective threat reduction both within the MPA and across other important habitats. Coordinated management across fisheries, shipping, offshore energy and defence sectors is essential. The Gully stands out as a rare conservation success in the open ocean, but its gains are not guaranteed.