Marine Protected Areas (MPAs) are being established worldwide to protect vulnerable marine species and habitats, in the face of accelerating rates of species extinctions. Biophysical indicators such as focal species abundance are often employed to assess the effectiveness of MPAs at meeting conservation objectives. We examined the dynamics of an Endangered beaked whale population 7 yr after the Gully MPA was established in 2004 off Nova Scotia, Canada. Northern bottlenose whales forage in deep

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... ater such as the Gully submarine canyon. Several MPA restrictions were implemented on the Gully ecosystem beginning in 2004 to reduce anthropogenic impacts including ship traffic, underwater noise and entanglements. This study represents the first intensive northern bottlenose whale population assessment since the Gully became a MPA. Using photo-identification data collected in 2010 and 2011, we applied mark-recapture techniques to estimate the current population size of northern bottlenose whales on the Scotian Shelf as 143 animals (95% CI: 129 to 156 animals). We also used open population models to examine population trends, and investigated changes in the sex ratio since 1988. Our results suggest the population size and sex ratio have been stable since before MPA legislation was implemented, illustrating the resilience of this population and suggesting that the MPA objective of preventing population decline is being met. Continued monitoring of MPA efficacy is necessary; there is still the potential for future events, whether stochastic or related to climate change, to affect small populations such as the Gully northern bottlenose whales and put the success of MPAs to further test.